ITMI20130710A1 - ELECTRONIC FILTER IN WAVE GUIDE WITH CAVITY 'RISONANTI A HIGH COUPLING. - Google Patents

Description

Title: "Electronic waveguide filter with highly coupled resonant cavities"

Description

The present invention relates to an electronic waveguide filter particularly suitable for high power applications, such as satellite telecommunications systems.

Frequency-selective passive devices with waveguide structure to filter signals in the microwave portion of the electromagnetic spectrum are widely used. In the field of satellite telecommunications, the recent trend is aimed at an ever greater increase in the number of channels and in the equivalent isotropic power transmitted (EIRP). The on-board telecommunication antennas usually have a diplexer at the entrance of the common antenna port to separate the bands dedicated respectively to transmission and reception. In general, a diplexer for satellite communications antennas must comply with several electrical and mechanical constraints. Relevant electrical constraints include low insertion loss (typically less than 0.1 dB) and low reflection coefficient (typically less than -25 dB) and high rejection bandwidth requirements (typically greater than 60 dB) ), together with very low values of passive intermodulation (typically lower than -120 dBm for 2 carriers of 250 W of power at the third order) and with sufficient confidence margins with respect to the triggering of electrical discharges in the vacuum, induced in the guide d ' wave due to the high electromagnetic field impressed by the many carriers which simultaneously insist on the component (and which create within a voltage envelope equivalent to tens of kW in a single carrier regime), the latter phenomenon also indicated by the English term multipaction. A frequency band widely used in commercial satellites, for example for television broadcasting, is the Ku band (12-18 GHz).

P. Sarasa et al. "Comparative Study of the Power Handling Capability of Space Broadband Antenna Filters inKu-banà", published at 5 <th> International Workshop on Multipactor, Corona and Intermodulation in Space RF Hardware, 12-14 September 2005, ESTEC (Holland), provide a comparative study of different broadband filter architectures in terms of their ability to handle high power levels. Among the different configurations analyzed, the filter architecture consisting of resonant slit cavities (stilb) short-circuited in plane E is indicated to be the most suitable for managing the highest power levels.

US patent 3,957,710 describes a waveguide band-pass filter consisting of the series connection of capacitive irises through rectangular waveguide sections whose height is tapered along the longitudinal axis. This configuration can be integrated with longitudinal slits in order to create a creperie filter (waffle-iron).

US patent 6,169,466 relates to a waveguide filter structure capable of handling signals in the microwave range. The filter described includes a waveguide adaptation section for each of the two access doors and a filtering section between the two adaptation sections. The filter section includes a lowered rectangular waveguide channel and a plurality of coupled resonant cavities, in which each resonant cavity consists of two symmetrical or asymmetrical stubs and is capable of introducing a reflection zero and two transmission zeroes into the frequency response of the filter.

A waveguide filter having a plurality of asymmetrical stub resonators is described in WO 00/55937. The waveguide filter comprises an input section, which includes a waveguide adapter and a low-pass filter, an output section, which includes a low-pass filter and a waveguide adapter, and a band pass filter inserted between the input and output sections. The band pass filter consists of a plurality of asymmetrical resonators, each resonator including a long slot and a short slot opposite each other and being capable of introducing at least one reflection zero and two transmission zeroes to the frequency response of the filter.

J.R. Montejo-Garai et al., “In-Line Pure -Piane Waveguide Band-Stop Filter with Wide Spurious-Free Responsé”, published in IEEE Microwave and Wireless Component Letters, vol. 21, no. 4, pp. 209-211, 2011, describe a coupling structure in the E plane between resonant cavities and rectangular waveguide suitable for the creation of stopband filters with in-line arrangement of the resonators. With the aim of obtaining a large margin of coupling values, the inductive iris conventionally adopted to connect each cavity to the rectangular waveguide has been replaced by a longitudinally asymmetrical slot. The article states that, in this way, the electric field is coupled on the total width of the waveguide instead of through a partial-width iris, producing greater coupling values. band rejection filter had a center frequency of 28 GHz and a percentage bandwidth of 2%. The Applicant has observed that a waveguide structure that provides a series of cavities with asymmetrical coupling slots can be complex to manufacture and be difficult to apply in broadband filters for high power applications.

Piotr Kozakowski, et al. in "New Resonator Arrangement far Reduced Size E-plane Filters", published in Microwave Symposium Digest (MTT), 2011 IEEE MTT-S, date of the international conference 5-10 June 2011, presents a filter in the E plane with a completely metallic insert consisting of by a series of resonators arranged alternately along Γ housing a ridge-type waveguide.

The Applicant has understood that reuse of a ridge type waveguide can significantly reduce the level of power managed in transmission by a filter.

So Hyeun Yun et ari in "Design of the Multipaction Free High Power Ka-Band Diplexer with an E-plane T-Junction '\ published in 2005 Asia-Pacifìc Conference on Communications (Perth, Western Australia), present a diplexer in guide d '' wave designed for satellite services operating in the K (18-26 GHz) and Ka (26-40 GHz) frequency bands and consisting of a stub filter in the E plane, a filter with inductive irises and a T junction in the E plane The diplexer described is said to be able to handle power levels up to 4.4 kW with sufficient confidence margins with respect to multipaction discharges.

According to one aspect, the present invention relates to an electronic waveguide filter configured to operate on electromagnetic signals in an operating frequency band, to transmit signals in a band of pass frequencies B1 and to reject signals within a band of frequencies. rejected frequencies B2, the passband and the rejected band being included in the operating band, the filter comprising a waveguide structure which comprises: a waveguide channel extending along a principal direction of propagation of electromagnetic signals in the operating band of frequencies and is delimited by a first side wall and a second side wall opposite the first side wall, the first and second side walls lying on respective planes that define a first and a second main reference plane, and a plurality of resonators spaced apart along the principal direction of propagation, each resonator comprising a resonant cavity formed in one of the first or second side walls and having an opening on the waveguide channel, in which the resonant cavities are arranged in alternating sequence on opposite side walls, and adjacent proximate resonant cavities arranged on respective opposite side walls are separated from each other by a longitudinal section of a connecting waveguide having a connection length, defined along the main direction of signal propagation, greater than or equal to zero and less than or equal to λ & 1/8, where λ & 1 is the length d wave guided at the central frequency of the pass band B1, the guided wavelength being the wavelength of the electromagnetic field associated with the fundamental mode which propagates along the waveguide channel.

The passband of the filter is defined as the frequency range in which the filter exhibits a high transmission coefficient between the input / output ports of the electromagnetic signals, preferably greater than -0.2 dB, more preferably greater than or equal to -0.1 dB .

The rejected band of the filter is defined as the frequency range in which the filter exhibits a high rejection coefficient between the input / output ports of the electromagnetic signals, preferably greater than or equal to 40 dB, more preferably greater than or equal to 50 dB.

Preferably, the filter comprises a rectangular waveguide structure on plane E.

Preferably, the connection length is greater than or equal to zero and less than or equal to λ & ι / 16.

In some particularly preferred embodiments, the connection length is between 0 and λ & ι / 24.

In some particularly preferred embodiments, the connection length is substantially equal to zero. In the present context and in accordance with the preferred embodiments, by connection length substantially equal to zero we mean a length less than λ & ι / 100, where λ & 1 is the guided wavelength corresponding to the central frequency of the pass band B1.

Preferably, the resonant cavities are stubs, each stub having a substantially rectangular cross section on the E plane defined by a stub height and a stub width, wherein the stub height is defined with reference to the sidewall reference plane in the which the resonant cavity is formed and the stub width corresponds to the opening of the resonant cavity on the waveguide channel. Preferably, the width of each stub of the plurality of stubs is between 0.08λ & ι and 0.35λ & 1.

Each stub has a central axis with respect to its opening on the waveguide channel, the central axis being perpendicular to the reference plane of the side wall in which the stub is formed. Preferably, the distance between the central axes of two adjacent and consecutive stubs (formed on opposite side walls) is between 0.15λ & ι and 0.35λ & 1, where λ & 1 is the wavelength guided to the central frequency of the pass band B 1.

Preferably, the resonant cavity has a defined height in a direction perpendicular to the reference plane of the side wall in which the resonant cavity is formed, the height being between 0.1 λ & 2 and 0.8λ & 2, where λ & 2 is the corresponding guided wavelength at the center frequency of the rejected band B2.

Preferably, the opening of the resonant cavities on the waveguide channel is between 0.08λ & ι and 0.35λ & 1, where λ & 1 is the guided wavelength corresponding to the central frequency of the pass band B1.

In the preferred embodiments, each resonator of the plurality of resonators comprises a step which is formed on the wall opposite the resonant cavity of the same resonator and which protrudes into the channel beyond the reference plane of the wall in which it is formed, each step facing a respective resonant cavity, the steps being arranged in a one-to-one correspondence with the respective resonant cavities.

Preferably, each resonator consists of a resonant cavity and a step structure formed in the side wall opposite to the side wall in which the resonant cavity is formed and in a same longitudinal waveguide section with respect to the main direction of propagation of the signals. , so that the resonant cavities and the step structures are arranged in alternating sequence on opposite side walls. Preferably, the resonant cavity is a stub.

Preferably, each resonant cavity has a width corresponding to the opening of the resonant cavity on the waveguide channel and the step opposite the resonant cavity has a step width along the direction of propagation of the signals substantially equal to the width of the resonant cavity.

Preferably, the step structure has a step height defined with reference to the reference plane of the side wall in which the step is formed, the step height being between 0 and 0.15λ & 1, where λ & 1 is the wavelength guided corresponding to the central frequency of the passband Bl.

In some embodiments, each resonant cavity has a cross section in plane E folded into a T or L shape to minimize clutter along the direction of field E and has a maximum coupling opening on the waveguide channel, preferably of width wk comprised between 0.08λ & ι and 0.35λ & 1.

In some preferred embodiments, the electronic filter is a band reject filter in which each resonator has at least one transmission zero at a frequency included in the rejected band B2 and at least one reflection zero at a frequency included in the pass band B1.

In some embodiments, the waveguide structure comprises a first input / output port, a second input / output port of the electromagnetic signals, the waveguide channel connecting the first with the second input / output port. exit.

Preferably, the side walls and the waveguide channel are formed in at least one metal unit. More preferably, the side walls and the waveguide channel are formed in a first and a second metal unit, the two metal units constituting two halves of a shell structure which can be joined together by mechanical closing means so as to forming a rectangular cross-section waveguide structure.

Preferably, the electromagnetic signals are satellite signals and the operating band is selected in the group consisting of C-band, X-band, Ku-band, K-band, Ka-band and Q-band. In one embodiment, the operating band corresponds to the Ku band between 10 GHz and 18 GHz (i.e. [10, 18] GHz).

In one aspect consistent with the present disclosure, a diplexer is provided which comprises a common access section for the input of electromagnetic signals in the operating frequency band, a transmission filter section and a receiving filter section, both sections of filter being coupled to the common access section so as to receive the electromagnetic signals entering the common section, wherein each filter section is a filter comprising the main features of the present invention.

In some embodiments, a multiplexer is provided which comprises a common access channel connected to a plurality of filters, at least one filter of which having the main characteristics of the filter of the present invention.

In one embodiment, a multiplexer is provided which includes a common access section for the input of electromagnetic signals in the operating frequency band and a plurality of filter sections, each filter section being configured to separate a sub-band of frequencies within the operating band so that different filter sections are configured to separate different sub-bands of frequencies. Each filter section of the multiplexer is coupled to the common access section and at least one filter section of the plurality of filter sections is a filter comprising the main features of the present invention.

The filter according to the present invention is particularly suitable for application in satellite telecommunications through on-board microwave antennas dedicated to FSS (Fixed Satellite Services) or BSS (Broadcast Satellite Services) and / or multimedia services operating in a multi-carrier regime with equivalent powers. of several tens of kilowatts.

Further features and advantages of the invention will result from the following detailed description made with reference to examples of implementation of the invention given for non-limiting purposes and the attached figures in which:

Figure la is a schematic perspective view of a rectangular waveguide band rejection filter that includes a resonator formed by a stub in the E plane.

Figure 1b is a view from the inlet port of the filter of Figure 1a.

Figure 1a is a longitudinal section of Figure 1a in plane AA.

Figure 2 is a graph showing the transmission (solid line) and reflection (dotted line) coefficients as a function of the frequency obtained from a numerical simulation for a waveguide filter having the structure of figures la- le.

Figure 3 is a section view in plane E of a band reject filter that includes two stub resonators arranged in series on the same waveguide wall and connected via a rectangular waveguide section.

Figures 4, 5, 6 are graphs showing the simulations of the transmission coefficients (solid line) and reflection (dotted line) as a function of the frequency for different values of the geometric parameters of the waveguide filter in figure 3.

Figure 7 shows a section view in plane E of a rectangular waveguide band rejection filter consisting of the series connection of two resonators, each comprising two opposing symmetrical stubs.

Figure 8 is a graph showing the transmission (solid line) and reflection (dotted line) coefficients as a function of the simulated frequency for a waveguide filter having the structure of figure 7.

Figure 9 is a sectional view in plane E of a band reject filter that includes two stub resonators arranged in alternating sequence on two opposite metal walls and connected via a rectangular waveguide section.

Figure 10 is a graph showing the simulation of the transmission coefficients (solid line) and reflection (dotted line) as a function of the frequency for a waveguide filter having the structure of figure 9.

Figure 11a is a schematic perspective view of a rectangular waveguide band rejection filter that includes a resonator formed by a stub and a step in the E plane.

Figure 1b is a view from the inlet port of the filter of Figure 11a.

Figure 1a is a longitudinal section of Figure 1a in the plane AA.

Figure 12 is a graph showing the transmission (solid line) and reflection (dashed line) coefficients as a function of frequency obtained from a numerical simulation for a waveguide filter having the structure of figures 1 la-1 le .

Figure 13 shows the section view in plane E of a rectangular waveguide band reject filter structure according to an embodiment of the present invention.

Figure 14 is a graph showing the simulation of the transmission coefficients (solid line) and reflection (dotted line) as a function of the frequency for a waveguide filter having the structure of figure 13.

Figure 15 shows the section in plane E of a filter structure rejecting a rectangular waveguide band according to an embodiment of the present invention in which the connection length between adjacent resonators is zero, Lk = 0.

Figure 16 is a graph showing the simulation of the transmission coefficients (solid line) and reflection (dotted line) as a function of the frequency for a waveguide filter having the structure of figure 15.

Figure 17 is a schematic representation of a section in plane E of a diplexer structure in a rectangular waveguide in accordance with an embodiment of the present invention.

Figure 18 shows a perspective view of a diplexer having the waveguide structure of figure 17 built with a metal shell structure, according to an embodiment of the present invention.

Figure 19 is a graph showing the simulated curve (solid line) and the measured curve (dashed line) as a function of the frequency of the reflection coefficient at the common port of a WR75 waveguide diplexer having the structure of figures 17- 18.

Figure 20 is a graph showing the simulated curve (solid line) and the measured curve (dashed line) as a function of the frequency of the transmission coefficient between the Tx and Rx gates of a WR75 waveguide diplexer having the structure of figures 17-18.

In the following, identical reference numbers in different figures indicate elements having the same or having the same functions.

Figure la is a schematic perspective view of an exemplary band-rejecting filter in a rectangular waveguide comprising a resonator formed by a resonant cavity consisting of a shorted stub (i.e., the slot is terminated on a metal wall) . Figure 1b is a view from the inlet port of the filter of Figure 1a, while Figure 1a is a longitudinal section in the plane AA of Figure 1b. The filter 1 comprises a rectangular waveguide channel 2 delimited in the plane AA by a first side wall 3 and a second side wall 4, opposite the first side wall. The first and second side walls are arranged on two respective main planes parallel to each other. The electromagnetic wave is confined inside the waveguide channel and propagates along a main direction of propagation of the electromagnetic signals indicated by the arrow 5, the latter corresponding to a direction substantially parallel to the first and second side walls of the wave guide. Figure la indicates the direction of the vector E of the incident electric field and the plane E is defined as the plane containing the vector É and the propagation direction vector 5, or, in figure 1b, the plane A A. The filter includes a stub 6 in the plane E of height hk which opens onto the waveguide channel with an opening of width Wk which defines the width wk of the stub. The waveguide channel has a rectangular section, in a plane perpendicular to the E plane, of width a and height b. The electromagnetic signals enter an input port 7 of the waveguide and exit from an output port 8, both in a respective plane perpendicular to the plane E. The stub acts as a resonant cavity by introducing a resonant frequency, i.e. a zero of transmission by the fundamental mode of the signals propagating along the waveguide. The frequency of the zero transmission is mainly determined by the size of the stub in the E plane, i.e. hk and wk. The transmission zero defines a band of rejected frequencies in which transmission is forbidden, or of frequencies at which the signal is strongly attenuated, indicated below with a rejected band. The passband of the filter is defined as the frequency range in which the filter exhibits a high transmission coefficient between the access ports, preferably greater than -0.2 dB.

The internal corners 9 and 10 of the stub (figure le) are rounded with a radius of curvature r, the value of which depends on the specific mechanical construction process adopted. In general, stub resonators are structures suitable for managing high levels of transmission power (Tx) without triggering multipaction phenomena. The dimensions Wke hk of the stub resonator are selected according to the passband and the rejected band to be obtained and the transmission and rejection capacity of the signals. The transmission and rejection capacity of a band rejection filter is usually represented by the transmission coefficient, Su, between the input and output ports of the waveguide (respectively, ports 7 and 8 in Figures 1a and 1) and by the coefficient of reflection, Up, at the input port of the waveguide.

Figure 2 is a graph showing the transmission (solid line) and reflection (dashed line) coefficients as a function of the frequency of a filter with structure of the filter 1 of Figures 1a-1c resulting from a numerical simulation. The waveguide considered in the simulation had dimensions a x b of 19.05 mm x 9.525 mm, corresponding to those required for a WR75 waveguide, which represents a standard of rectangular waveguide used in the band [10, 15] GHz. The dimensions of the stub were Wk = 4 mm, / 3⁄4 = 4, 1 mm and r = 0.5 mm. The transmission coefficient has a zero at a frequency of 14.5 GHz. The graph shows a passband B1 in the frequency range from 9 to 12 GHz (28.6% of the percentage band referred to the central frequency of the passband Bl ) and a rejected band B2 from 13 to 16 GHz (20.7% of the percentage band referred to the central frequency of the rejected band B2). The transition percentage band between B1 and B2 is equal to 8% (referred to the central frequency of the transition band 12-13 GHz).

If on the one hand, as the stub width increases, the filter capacities increase both for rejection (resulting from a greater coupling with the channel in the rectangular guide) and for managing high transmission powers (due to the increase in the equivalent voltage necessary for 'triggering of discharges by multipaction), a large width of the stub results in insufficiently low reflection coefficient values within the passband B1. With reference to Figure 2, the reflection coefficient Su has an amplitude lower than -10 dB in the band B1. For example, this value grows to -7 dB for a structure with wk = 8 mm and hk = 3.8 and in which the other structural parameters remain unchanged compared to the previous numerical example. Furthermore, in practice and in the context of commonly used electronic waveguide filter manufacturing technologies (for example, milling and EDM), there is a lower limit on the width of the stub. This value is typically defined by the size of the tools used to form the structural discontinuities in the waveguide walls.

A resonator configuration having a high reflection coefficient is particularly disadvantageous for the realization of broadband filters, obtained by cascading several resonators. In fact, high levels of reflection coefficients of the individual resonators generate a high standing wave between the resonators that make up the filters, not allowing to obtain low levels of reflection coefficient, losses and phase distortion over a wide band and limiting the maximum level of transmission power of the filters.

The Applicant has observed that the presence of higher order propagation modes along the rectangular waveguide of a broadband filter which provides two close and adjacent resonators can considerably deteriorate the rejection level in the rejected band due to the electromagnetic interaction. between the two resonators through the first two higher order modes, TEn and TMn, of the waveguide connecting the resonators. The deterioration is to be understood with respect to the performance obtained as a result of an electromagnetic interaction between two adjacent resonators only through the fundamental mode (TEi0) of the rectangular guide.

Figure 3 shows a sectional view in plane E of a filter 17 which comprises two resonators consisting of a respective stub 18 and 19, each of which, for simplicity of description, having the same structure as that of the resonator 1 shown in figure la- lc. Stub 18 has height hk and width while stub 19 has height hk + i and width Wk + i. The stubs are connected in series along the direction of propagation 5 of the signals, i.e. along the waveguide channel delimited by the side walls 3 and 4 and having an input port 7 and an output port 8. The two stubs 18 and 19 are spaced apart by a longitudinal waveguide section 20 of length Lk, defined along the direction of propagation of the signals and of height bk, corresponding to the distance between the side walls in the waveguide section between the two stubs . The longitudinal section of the waveguide that separates two adjacent neighboring resonators will be indicated below with the connection section, while its length Lk with the connection length. In the structure of figure 3 the connection section has a rectangular cross section in the E plane.

It should be understood that the height bk of the connection section between the two resonators 18 and 19 may be different from the height b of the waveguide at the input and output ports, 7 and 8, of the filter. In particular, a decrease in the height bk allows to increase the rejection of the filter in the rejected band, but to the detriment of the other figures of merit, such as the reflection coefficient in the passband and the ability to manage high transmission powers, thus making the architecture does not comply with the technical specifications imposed in many applications.

Figure 4 is a graph showing the transmission and reflection coefficients (dashed line) resulting from a numerical simulation as a function of frequency for a filter with structure described with reference to Figure 3. The wave guide considered in the simulation whose results are reported in figure 4 had dimensions a x b of 19.05 mm x 9.525 mm, corresponding to those of a WR75 waveguide, wk = wk + i = 4.0 mm, hk = hk + i = A, \ mm , Lk = 3.0mm, bk = b and r = 0.5mm. The transmission coefficient S2i represented with a dash-dot line in Figure 4 is the result of a simulation in which it is assumed that the electromagnetic interaction between the resonators 18 and 19 occurs through the only fundamental mode of the waveguide for which it is foreseen. a double zero of transmission at about 14.5 GHz. The transmission coefficient S2i represented by the solid line in figure 4 is the result of a simulation in which it is assumed that the interaction between the two resonators also occurs through the higher order modes. A considerable degradation of the rejection capacity of filter 17 in rejected band B2 can be observed in the case of multi-modal interaction between the resonators. This phenomenon is caused by the strong multi-modal interaction between resonators 18 and 19 and, in particular, by an electromagnetic interaction associated with the first two higher-order modes of the waveguide. This interaction is established due to the insufficiently low attenuation of the modes TEn and TMn introduced by the rectangular waveguide section 20 which has a reduced electrical length, where the electrical length is defined as the ratio between the length Lk and the length d guided wave X in the waveguide.

The guided wavelength associated with the fundamental mode that propagates in a rectangular waveguide is equal to

where λ is the wavelength in free space.

For example, the guided wavelength λ & 0 in a WR75 rectangular guide at the center frequency /0=12.5 GHz of the operating band [10, 15] GHz is approximately 30 mm, so the electrical length of the waveguide section between the two adjacent stubs of figure 3 it is equal to about 1/10.

The Applicant has considered, as a possible solution to this problem, an increase in the electrical length of the connection section 20 by an amount equal to λ & 2/2 (connection section working on the second resonance). Figure 5 shows the transmission (solid line) and reflection (dashed line) coefficients as a function of the frequency simulated by the computer of a filter such as that of figure 3. Compared to the simulation of figure 4, in the simulation of figure 5 it is only the length Lk of the section of the rectangular waveguide 20 has changed between the resonators 18 and 19, the value of which is equal to 15 mm, i.e. 5 times the value used in the simulation of figure 4. In particular, to the value of Lk of the simulation of figure 4, a quantity equal to 12 mm has been added, corresponding to λ & 2/2 at the central frequency of the rejected band /2=14.5 GHz. resonators 18 and 19 caused by the higher order modes of the rectangular guide, restoring the presence, in the rejected band B2, of two zeros of the transmission coefficient 3⁄4i.

However, the Applicant has noted that this technological solution aggravates the bulk and mass of the filters and reduces their bandwidth due to the considerable phase rotation introduced by the connection section, thus resulting not feasible in many applications of interest. .

A second possible solution for reducing the multi-modal interaction between the resonators was considered, which involves the use of a lowered rectangular waveguide, or a rectangular waveguide in which the height b is reduced. . The graph in figure 6 shows the simulated transmission (solid line) and reflection (dashed line) coefficients as a function of the frequency of a filter with a structure like that of figure 3, in which the dimensions of the lowered rectangular guide a x b are equal to 19 , 05mm x 5mm and wk = wk +; = 4.0mm, hk = hk + i = 5.4mm, Lk = 3.0mm, bk = b and r = 0.5mm. The variation of the values of the parameters hk compared to those of the geometry to which the simulations shown in Figures 4 and 5 refer compensates for the variation of the height b of the guide in which the two resonators are inserted. Although the two transmission zeros are not present on the real frequency axis, the transmission coefficient Sj \ of the filter in the lowered rectangular waveguide has adequate rejection in the rejected band with a minimum at levels of -30 dB in the center band B2.

The Applicant has observed that this technological solution has strong limitations in terms of maximum power that can be managed in transmission, consequent to higher electric field levels in the internal structure of the filter with the same incident power, insertion losses, consequent to lower electric currents. high that flow on the side walls of the filter, and of reflection coefficient in the passband.

A third possible solution applicable to filters in rectangular guides to obviate the interaction between adjacent resonators that occurs through the TEn and TMn modes involves symmetrizing the structure of the resonators. Figure 7 shows a section view in plane E of a rectangular waveguide band rejection filter in plane E which includes two symmetrical resonators, each consisting of two identical opposing stubs. The filter comprises a waveguide channel 2 delimited in the plane E by a first and a second side wall 3, 4. Two stubs 21a and 21b are arranged in series on the first side wall 3, facing two respective stubs 22a and 22b formed on the second side wall 4, opposite the first side wall. Each pair of opposing stubs (i.e. 21a, 22a and 21b, 22b) creates a resonant cavity characterized by a resonant frequency. The heights hke hk + 1 and the widths wke wk + 1 of the two stubs making up each resonator are identical and are determined, for each resonator, on the basis of the resonant frequency and quality factor required for each resonator in order to obtain the desired frequency response. filter. In a waveguide with a plurality of symmetrical stub resonators of the type shown in Figure 7, the electromagnetic interaction between the proximate and adjacent resonators along the direction of propagation of the signals occurs essentially only through the fundamental mode since the two modes of higher order TEn and TMn are not excited by symmetry.

Figure 8 is a graph showing the transmission (solid line) and reflection (dashed line) coefficients as a function of the frequency resulting from a numerical simulation of a filter having the structure of figure 7 and connection length Lk = 3.0 mm. The dimensions of the waveguide considered in the simulation complies with the technical specifications WR75 and the two symmetrical resonators 2 la, 22a and 21b, 22b have the same dimensions wk = wk +; = 4.0 mm, hk = hk +] = 5.4 mm, bk = b, and r = 0.5. Since the two resonant cavities have the same size, each defines a transmission zero at the same frequency and equal to 14.5 GHz. The transmission coefficient, S2i, of the filter is attenuated in the rejected band presenting a minimum in the middle band B2 of approximately -35 dB (equivalent to two transmission zeros in the complex plane close to the real frequency axis). Despite the presence of a zero reflection at the frequency of 11 GHz, the filter exhibits a significant reflection coefficient, Su, in the passband with a maximum value of -4 dB at the upper cut-off frequency of the passband, i.e. 12 GHz. Without wishing to be bound by a particular theory or explanation, this behavior is caused by a greater mismatch at the input ports of each resonator having the symmetrical structure shown in figure 7 compared to the single stub structure shown in figures la. Consequently, filters with a wide bandwidth can be implemented with this architectural solution by resorting to a greater number of resonators. Alternatively, the reflection coefficient of the filter in Figure 7 can be decreased near the upper cut-off frequency of the passband by moving the zero of the reflection coefficient on the real frequency axis, or by reducing the connection length Z *. ; The Applicant has, however, observed that the manufacture of metal waveguides with symmetrical resonant cavities and connection lengths of less than about 4-6 mm can become problematic from a mechanical point of view. For example, in a mechanical construction formed by two clamshett metal units, a screw cannot be inserted and / or tightened well between one cavity and the next so that a good closure is not guaranteed between the metal parts that form the waveguide resulting in increased signal losses along the guide. The Applicant has understood that a waveguide filter structure which provides a plurality of resonant cavities arranged alternately on the first side wall and on the second side wall along the direction of propagation of the signals allows to considerably reduce the influence of the modes of higher order TEn and TMn on the rejection of the filter in the rejected band without an appreciable deterioration of the other figures of merit of the filter. ; Figure 9 is a section view in plane E of a band reject filter that includes two stub resonator arranged in alternating sequence on two opposite metal walls and connected via a rectangular waveguide section. The waveguide filter structure 23 provides two stub resonators 24 and 25 arranged alternately on the first side wall 27 and on the second side wall 28 along the direction of propagation 5 of the signals. The side walls delimit the waveguide channel 2. The two resonators 24 and 25 formed on the two opposite side walls 27 and 28 are connected by means of a rectangular waveguide section of height bk and length Lk, or by means of a section of connection. ; Figure 10 shows the transmission (solid line) and reflection (dashed line) coefficients as a function of the frequency simulated for a filter structure of Figure 9 with two stubs arranged alternately on the opposite walls of a rectangular waveguide. The geometric parameters assume the same values as those of the example of figure 4 for a filter having the structure of figure 3, i.e. a x b equal to 19.05 mm x 9.525 mm, corresponding to those of a WR75 waveguide, wk = wk +; = 4.0 mm, hk = hk +] = 4J mm, Lk = 3.0 mm, bk = b and r = 0.5 mm. The transmission coefficient, S2i, has two zeros on the real axis of the frequencies in the rejected band, respectively at about 13.75 GHz and 15.75 GHz. Without wishing to be bound by any theory or explanation, the shift of the transmission zeros from the nominal position of 14.5 GHz is due to the reduced residual multi-modal interaction between the two resonators. At the same time, the filter exhibits a reflection coefficient lower than -16 dB in the entire passband with a zero at the frequency of 11.7 GHz.; The Applicant has understood that the connection lengths Lktra successive resonators obtained on opposite walls are not critical. from a mechanical point of view. It is therefore possible to size the connection length in order to maximize the electrical performance of the broadband filters, in particular but not exclusively, in order to minimize the reflection coefficient of the passband filter. ; It has been observed that, even for structures in which the connection lengths are less than about 4 mm, there are no mechanical elements of critical dimensions that can compromise the construction and mechanical assembly in a mechanical construction of the clamshell type. In particular, it has been found that a waveguide filter comprising a plurality of resonant cavities arranged alternately on the opposite side walls along the waveguide channel with a connection length between successive resonators that is very small or substantially zero allows to obtain the maximum electrical coupling between adjacent resonators along the direction of propagation of the signals as the width wk of each resonator can be maximized. This aspect allows to have resonators with a wider opening width on the waveguide channel and, therefore, to manage a higher level of transmission power without triggering discharge phenomena due to multipaction. Advantageously, the substantial absence of the connection sections reduces the dimensions and weight of the generally metallic structure of the filter. According to a main aspect consistent with the present disclosure, the longitudinal section of the waveguide has a connection length along the main direction of propagation of the signals less than or equal to λ & 1/8, where λ & 1 is the guided wavelength corresponding to the frequency center of the passband. Preferably, the connection length is equal to or less than λ & ι / 16. The Applicant has understood that, in some preferred embodiments, the insertion of a step which protrudes inside the waveguide channel and which faces a resonant cavity (stub) arranged in the opposite side wall increases the filter design flexibility The Applicant has realized that the alternating arrangement of the resonant cavities on the lateral walls of the waveguide is applicable to filters with resonators having a composite stub-step structure, thus obtaining mechanical manufacturing flexibility and a reduction in the multimodal interaction between adjacent resonators, even for small or very small connection lengths. In particular, it has been found that the connection length can be reduced to zero without introducing a significant deterioration of the overall structure rejection. ; Figures 11a-llc show the perspective view, the front view and the sectional view in plane E of an exemplary band reject filter 11 in a rectangular waveguide whose waveguide structure comprises a single resonator consisting of a stub and by one step. A step 12 is formed in the same longitudinal waveguide section which includes a stub 29 formed in the opposite side 3 with respect to the side wall 4 in which the step is formed. Step 12 includes a first vertical wall 13 and a second vertical wall 14 which delimit it laterally and define its extension within the waveguide channel along the direction of propagation of the electromagnetic signals. The vertical walls 13, 14 of the step have a height hk 'with respect to the reference plane of the side wall 4. Preferably, the positions of the walls 13 and 14 of the step along the propagation axis 5 are respectively aligned with those 15 and 16 of the stub for reasons of mechanical simplicity and design. In these preferred embodiments, therefore, the width wk of step 12 coincides with that wk of stub 29.; The insertion of step 12 increases the design flexibility of the resonator, since a variation of its height hk involves a variation of the reflection coefficient of the resonator in pass band B1 without substantially modifying the insulation characteristics of the rejected band resonator. In particular, the Applicant has observed that it is possible to configure a composite stubstep resonator so as to produce a transmission zero in rejected band B2 and a reflection zero in passband B 1.; Figure 12 is a graph showing the coefficients of transmission (solid line) and reflection (dashed line) resulting from a computer simulation as a function of the frequency of a filter having the structure of the filter 11 of Figures 11a. The waveguide considered in the simulation had dimensions a x b of 19.05 mm x 9.525 mm, corresponding to those of a WR75 waveguide, wk '= wk = 4.0 mm, hk = 4.45 mm, hk = 2.0 mm and r = 0.5 mm. The transmission coefficient Sj \ has a zero in the rejected band B2 at a frequency of 14.5 GHz and a reflection coefficient Sucon a zero in the bandwidth B1 at a frequency of 9.5 GHz. step of figure lla-llc allows to increase the width wk of the stub, thus improving the performance of the filter in terms of transmission power management and rejection in the rejected band, while ensuring relatively low values of reflection coefficient in the passband Bl, i.e. Up below about -15 dB in the Bl band (figure 12). Figure 13 schematically shows the cross section in plane E of a structure of a rectangular waveguide 40 for a band reject filter according to an embodiment of the present invention. The waveguide structure comprises a rectangular waveguide channel 2 (i.e. with a rectangular section in a plane perpendicular to plane E) delimited by a first side wall 39 and by a second side wall 41, opposite the first side wall . The first and second waveguide side walls have a respective main reference plane 37 and 38 defined as the main plane on which the respective side wall lies. The electromagnetic signals enter the waveguide channel 2 along the main direction of propagation indicated in the figure with the arrow 5, generally parallel to the reference planes 37, 38 of the side walls which are preferably parallel to each other. ; Preferably, the rectangular waveguide channel has a width a greater than λπΐ3χ / 2, where λΙΤ13χ is the wavelength in free space corresponding to the minimum frequency / m in the operating frequency band of the filter. The operating band is defined as a frequency range including the pass band B1 and the rejected rejected band B2. The distance b between the opposite side walls, defined as the distance between the reference planes of the respective side walls, is preferably equal to or less than all. In some embodiments, the values of a and b conform to the rectangular waveguide standards used in satellite communications filters. ; For example, in a WR75 rectangular waveguide structure used in the 10 to 15 GHz frequency band, approximately corresponding to the Ku frequency band, ληΐ3χ = 30 mm corresponds to the frequency / min = 10 GHz and the guide channel wave has dimensions a = 19.05 mm and b = 9.525 mm. ; The waveguide structure 40 comprises a plurality of n resonant cavities 1 ..., k-1, k, k + 1, ..., n arranged in alternating sequence on opposite side walls along the principal direction of propagation and spaced from each other by longitudinal waveguide sections of length Lk. In particular, two adjacent resonant cavities adjacent to the plurality of n resonant cavities are formed on opposite side walls and are separated by a longitudinal waveguide section, or by a connection section. The connection section between two adjacent proximate resonant cavities is preferably free of discontinuity. In other words, the opposite side walls, in correspondence with the connection section, extend along the respective reference planes. In most cases of interest, this condition implies that the height bk of the connection section is equal to the height b of the waveguide at the entrance (and exit) of the waveguide channel. ; In the example in Figure 13, the waveguide structure of the filter comprises five resonant stub cavities 42, 43, 44, 30 and 31 formed alternately in the side walls 39, 41 of the waveguide. ; Preferably, in the filter, for each stub arranged in a certain longitudinal section of the waveguide, there is a step arranged on the side wall opposite to that of the respective stub and in correspondence with the same determined longitudinal section of the waveguide. The steps are then arranged in alternating sequence along opposite side walls. In the present embodiment, the filter comprises a plurality of resonators arranged in sequence along the main waveguide direction, each resonator comprising a resonant stub cavity and a step arranged on the side wall opposite to that of the respective stub, so such that the resonant cavities of each resonator are arranged opposite to corresponding steps in a one to one correspondence. In figure 13, the steps of the respective resonators are indicated with 42 ', 43', 44 ', 30' and 3Γ. Preferably, the arrangement of the stubs and steps is such that the axis in a direction perpendicular to the reference plane of the side wall in which each stub is formed and central with respect to the main dimension of the waveguide substantially coincides with the central axis of the opposite step. The respective central axes of the five filter resonators are indicated in figure 13 with the reference numbers 32, 33, 34, 35, 36.; The heights hk and hk \ respectively, of the stub k and of the step k of the resonator k (k = Ι ,.,. ή) are defined as the maximum height with respect to the reference plane of the respective side wall, e.g. along their respective central axis. Preferably, the height hk of the stub can assume values between 0.1 λ & 2 and 0.8λ & 2, where λ & 2 is the guided wavelength corresponding to the central frequency of the rejected band B2. The value λ & 2 can be selected within the range indicated above depending on the working regime in which the stub is operated, or on the order of the resonance that is used. ; Preferably, the height hk of the step of each resonator is between 0 and bl 2, where b is the height of the wave guide, defined by the distance between the two reference planes 37, 38 of the side walls. In some particularly preferred forms, the height of the step of each resonator is between 0 and 0.15λ & 1, where λ & 1 is the guided wavelength corresponding to the central frequency of the pass band Bl. In this context, a resonator having a step height value equal to zero (i.e. hk '= 0) consists of a stub formed on a side wall while the section of the opposite side wall arranged in correspondence with the stub coincides with the reference plane of this opposite side wall. Preferably, the plurality of resonators comprises a respective plurality of stubs and a plurality of steps, the steps being arranged in a one-to-one correspondence with the stubs, each step being arranged on the side wall opposite to that of the respective stub. ; The width wk and wk of the stub and step is defined as the opening of the stub and step, respectively, on the waveguide channel. Preferably, the width of the step is equal to the width of the stub arranged opposite to the step, that is, in the example of figure 13, wk = wk. While not strictly necessary, selecting substantially equal widths of stubs and opposite steps can reduce filter design complexity by limiting the number of design variables without affecting the flexibility of the structure in terms of operating bandwidth and positioning of the reflection zeroes in the passband and of the transmission zeroes in the rejected band. ; In the present context, substantially equal widths mean two width values that differ from each other by a value not greater than Aw = 0.01 mm, or wk '= wi ≠: 0.01 mm (value substantially defined by the tolerances of mechanical processing). ; The opening wk of the stub on the waveguide channel determines both the electromagnetic coupling between the £ -th resonant cavity and the waveguide channel, i.e. the rejection of the resonator, and the power level that can be managed in transmission. Since the level of power managed in transmission without the occurrence of discharge phenomena in the multipaction filter is inversely proportional to the distance between parallel metal walls facing each other, the Applicant has understood that it is particularly advantageous for the opening wk of each stub to be maximized. Preferably, the connection length along the main waveguide direction between two adjacent adjacent resonant cavities is less than or equal to λ & 1/8, where λ6ι is the guided wavelength corresponding to the central frequency of the pass band. More preferably, the connection length is less than or equal to λ & ι / 16. In some embodiments, the connection length is between 0 and λ & ι / 24. In some particularly preferred embodiments, Lk = 0. ; The distance dkbetween the respective central axes of two consecutive stubs adjacent to each other, or of two adjacent resonators, is a parameter that at least partially determines the passband of the filter and the presence or absence of spurious zeros of reflection in the rejected band. Therefore, the parameter can be selected in such a way that spurious reflecting zeros are absent in the rejected band. In general, the value dk depends on the phase of the reflection coefficients of the two adjacent resonators and varies according to the width of the pass band. ; Preferably, dk is included in the interval between 0.15λ & ι and 0.35λ & 1, where λ & 1 is the guided wavelength corresponding to the central frequency of the pass band. ; The height bk of each longitudinal waveguide section interposed between two adjacent neighboring resonators, i.e. the height of the connection section, is preferably equal to or greater than the height b of the waveguide to the access doors (i.e. doors input / output), in order to reduce the probability of multipaction phenomena occurring between the opposite side walls of the waveguide and / or insertion losses. In some preferred embodiments, bk = b, for k = 1, ..., n. In other embodiments, the heights bk of the connection waveguide sections interposed between adjacent neighboring resonators can be the same or different from each other. ; Depending on the electrical characteristics of the filter to be obtained, the heights hk of the stubs, the heights hk of the steps, and the respective widths wk and wk can be the same or different for each resonator k = 1, ..., n. ; The lengths Jk of the waveguide connection sections interposed between adjacent neighboring resonators can be the same or different from each other. ; The side walls and the waveguide channel can be formed by means of known mechanical techniques, for example electro-erosion and milling, on a first metal unit which can constitute one half of a shell which joined to a second metal unit with the same structure of waveguide forms the other half of a clamshell type filter. In the embodiment of Figure 13, the section in the plane E of the stub and of the step of each resonator has a rectangular shape with rounded edges corresponding to convex corners. However, the geometry of the stubs and the steps of the individual resonators can vary in consideration of the coupling parameters to be obtained and any mechanical requirements to be met. The shape is in many practical cases determined by the manufacturing process of the waveguide. By way of example, the stubs can have a T-shaped or L-folded shape to minimize the encumbrance along the direction of the E field, however, presenting an opening wka maximum coupling with the waveguide channel. ; For example, an approximately rectangular cross section of stubs and steps, i.e. whose radii of curvature r of the edges are small (less than 0.1 -0.2 mm), can be obtained by making the metal structure of the waveguide by electroerosion. In some applications, however, this manufacturing technique may involve greater mechanical complexity with an increase in costs and execution times. ; Again by way of example, cross sections with rounded edges at convex angles in the geometry of the resonators are typically obtained with sufficient reliability and average quality of the mechanical construction by milling, provided that a radius of curvature greater than or equal to a quarter of the digging depth in order to guarantee the stability of the tool. Figure 14 is a graph showing the transmission coefficients S2i (solid line) and reflection Su (dashed line) resulting from a numerical simulation, as a function of the frequency for a filter with the structure of Figure 13 and comprising 5 resonators. The filter was designed for a passband B1 in the frequency range from 9 to 12 GHz and a rejected band B2 from 13 to 16 GHz.; The wave guide considered in the simulation of figure 14 had dimensions a x b of 19.05 mm x 9.525 mm, corresponding to those of a WR75 waveguide. The heights bk and the lengths Jk of the connection sections were constant for k = 1, 2, 3, 4, 5 and equal to 9.525 mm and 1.00 mm, respectively. The heights hk and the openings wk of the stubs of each resonator vary, respectively, in the range between 4.0 mm and 4.6 mm, and in the range between 4.0 mm and 6.4 mm. The heights of the steps hk are between 1.0 and 1.5 mm. Due to the limited electromagnetic interaction between the resonators through the higher order modes, the filter has a transmission coefficient S21 in which the five zeros are present which would be predictable on the basis of an ideal model in which the interaction between the resonators occurs by means of the only fundamental mode of the waveguide. Consequently, the filter has a strong rejection in rejected band B2 higher than 40 dB. Furthermore, the filter exhibits a reflection coefficient Su with an equìpple behavior lower than -28 dB with four reflection zeros. Without wishing to be bound by any particular explanation, it is assumed that the reflection zeros originate from the presence of the four connection sections, located in the passband Bl. Figure 15 shows the cross section in plane E of a waveguide band reject filter structure 50 according to an embodiment of the present invention, comprising a plurality of n resonants 1 ..., k- 1, k, k + 1, ..., n, in which each resonator consists of a stub and a step, the stubs being arranged in alternating sequence on the opposite side walls 55, 56 which delimit the waveguide channel along the propagation direction 5 of the electromagnetic signals and in which the connection length between adjacent resonators is zero, Lk = 0. In this condition, adjacent resonators are contiguous to each other, i.e. along the surface of the first side wall 55 that faces the channel the stub 53 of the generic resonator k has the edge 57 in common with the step 54 'of the resonator k + 1 and, at the same time, along the opposite surface of the second side wall that faces channel 56, the step 53' of the generic resonator k has in common the s peep 57 'with the stub 54 of the k + 1 resonator. resonators and the waveguide, as the opening of the stubs on the waveguide channel can be maximized with a consequent increase in the filter's ability to handle high powers without multipaction problems even in broadband applications. ; In many embodiments, it is not necessary to reduce the height b of the waveguide to eliminate the presence of higher order signal propagation modes. ; In the example in figure 15 the waveguide structure comprises five resonators, where each resonator is composed of a stub and a step, preferably with the same width (<'> wk = wk ^ and with central axes arranged in the same position longitudinal in order to minimize the design complexity without introducing a degradation of the performances. The heights hk of the stubs, the heights hk of the steps and the respective widths wk can be the same or different for each resonator on the basis of the electrical and mechanical specifications imposed on a particular implementation of this architectural solution.; It is observed that a waveguide filter structure of the type of figures 13 and 15 has a low sensitivity to manufacturing errors since the alternating sequence arrangement of the resonators allows both to maximize the distance between facing metal surfaces and parallel, thus increasing the manufacturing accuracy for milling, is to insert mechanical means closing anices (e.g. screws and alignment pins) in order to ensure a good tightening of the mechanical parts by means of common assembly techniques. ; The transmission (solid line) and reflection (dashed line) coefficients as a function of the frequency of a filter with the structure of figure 15 resulting from a numerical simulation are shown in figure 16. The wave guide considered in the simulation had dimensions a x b of 19.05 mm x 9.525 mm, corresponding to those of a WR75 waveguide. The heights hk and the openings wk of the stubs vary, respectively, between 3.8 mm and 4.2 mm, and between 4.2 mm and 7.2 mm. The heights of the steps are between 1.0 and 1.5 mm. It is observed that the performances of the exemplary filter with Lk = 0 are calculated to be similar to those of the filter of figure 13 relating to the filter architecture with connection lengths equal to 1 mm, in terms of adaptation in passband B1 and rejection in rejected band B2 shown in figure 14. In the case of figure 15, the absence of connection sections that separate adjacent resonators allows to maximize the coupling between the resonators and the wave guide, or to maximize the level of power that can be managed in transmission. ; The waveguide filter structure described above can be adopted to realize a multiplexer device which implements the frequency multiplexing of the channels, such as for example diplexer (two channels) and triplexer (three channels), operating for example in a band of frequency corresponding to the operating band C (4 GHz to 8 GHz), the Q band (30 GHz to 50 GHz) or the V band (50 GHz to 75 GHz). According to some preferred embodiments, the device operates in the spectral region between 10 and 18 GHz, corresponding to the Ku frequency band for satellite telecommunications. Preferably, the multiplexer operates in a spectral band between 4 and 60 GHz which includes the satellite frequency bands C, X, Ku, K, Ka, Q and V. However, it is to be understood that the present invention is not limited to a specific range of operating frequencies. A filter according to the general teachings of the present invention can be used as a base element in a diplexer device. ; The diplexer can be designed to divide a band of frequencies into sub-bands or to combine two sub-bands of frequencies into a band of frequencies. ; Figure 17 is a schematic representation of a cross section in plane E of a rectangular waveguide structure of a diplexer to separate a frequency band into two sub-bands, according to an embodiment of the present invention. The figure shows the cross section of a waveguide channel, while the side walls of the waveguide are not shown. A diplexer 60 comprises an access section 61 connected to a transmission filter section 63 and to a reception filter section 64, the access and filter sections being indicated in the figure with a rectangle with a dash-dot line. The filter sections 63 and 64 of the diplexer each comprise a waveguide structure having an architecture similar to that of the waveguide structure 50 of Figure 15, i.e. comprising a plurality of stub-step composite resonators whose stubs and steps they are arranged in alternating sequence along opposite side walls of the respective waveguide channel with adjacent next resonators which are contiguous to each other (Z * = 0). The access section 61 is provided with an access door 62, in common for the signals in the two sub-bands in transmission (Tx) and in reception (Rx), from which the electromagnetic signals in the Rx band enter and go into the channel in waveguide 66 which acts as a reception channel and to which the electromagnetic signals in the Tx band arrive from the waveguide channel 65 which acts as a transmission channel. The common access section 61 comprises an input waveguide channel 67 in which adaptation elements, such as steps, are inserted in one of its side walls 68 and a bifurcation 69 which connects the input waveguide channel to the transmission and reception channels 65, 66 The transmission and reception waveguide channels are physically separated from each other and each have an output port 70, 71 for the Tx and Rx channels respectively.

Figure 18 shows a perspective view of a diplexer having the waveguide structure of figure 17 and built with a shell structure comprising two metal units 72 and 73 which constitute two halves of the shell which can be joined together by means of closure mechanical to form a rectangular waveguide structure. Figure 18 shows the two halves of the common access gate 62 for the transmission and reception signals which, when combined, form a waveguide gate with a rectangular section, and one half (with respect to the plane of symmetry E) of the guide d access wave 67 and of the transmission waveguide 65 which constitutes the Tx channel. Only partially visible in figure 18 is the receiving waveguide 66 which constitutes the Rx channel.

According to known techniques, the waveguide channels are obtained by hollowing out the metal, preferably an aluminum alloy, by numerical control milling and, subsequently, the internal metal walls of the waveguide are subjected to a passivation or silvering for the purpose, respectively, of preventing surface oxidation or improving surface conductivity. The type of surface treatment may also depend on the specifics imposed on the power level to be managed in transmission without triggering discharges due to the multipaction effect.

Figures 19 and 20 show the comparison between the simulated curves (solid line) and the measured curves (dashed line), respectively, of the reflection coefficient at the common port 62 (Figure 19) and of the transmission coefficient between the Tx and Rx ports 70, 71 (figure 20) of an embodiment of the diplexer of figure 18 in the WR75 guide operating in the bands Tx = (10.7 GHz, 12.8 GHz) and Rx = (13.7 GHz, 14.5 GHz). There is a remarkable agreement between the measured and simulated curves as regards both the levels and the position of the zeroes of the curves, with a measured reflection coefficient lower than -30 dB and an insulation measured between the two Tx and Rx ports higher than 60 dB on both the Tx and Rx bands.

The maximum power level that can be managed in a single carrier system without any multipaction discharge phenomena being triggered is 14.5 kW, equivalent to a condition of 14 carriers of 260 W each (evaluation carried out according to the ESA recommendation "20-gap -crossing ”with a confidence margin of 6 dB). Finally, the insertion losses and the derivative of the group delay of the diplexer are lower, respectively, than 0.1 dB and 0.1 ns / 50 MHz on both bands (Tx and Rx).

Claims (12)

Claims 1. An electronic waveguide filter (40, 50) configured to operate on electromagnetic signals in an operating frequency band, to transmit signals in a frequency band B1 and to reject signals within a rejected band of frequencies B2, the passband and the rejected band being included in the operating band, the filter comprising a waveguide structure which comprises: a waveguide channel (2) which extends along a main direction (5) of propagation of electromagnetic signals in the operating frequency band and is delimited by a first side wall (39; 55) and by a second side wall ( 41; 56) opposite the first side wall, the first and second side walls lying on respective first and second main reference planes (37,38; 51,52), and a plurality of resonators spaced from each other along the main direction propagation, each resonator comprising a resonant cavity formed in one of the first or second side walls and having an opening on the waveguide channel, in which the resonant cavities are arranged in alternating sequence on opposite side walls, and adjacent proximate resonant cavities arranged on respective opposite side walls are separated from each other by a connecting waveguide longitudinal section having a connecting length, defined along the main direction propagation of signals, greater than or equal to zero and less than or equal to λ & 1/8, where λ & 1 is the wavelength guided to the central frequency of the passband Bl. 2. The filter of claim 1, in which the waveguide is a rectangular waveguide structure on plane E. The filter of claim 1 or 2, wherein the connection length is substantially equal to zero. The filter according to one of the preceding claims, wherein the resonant cavities are stubs having a cross section on the rectangular E plane defined by a stub height and a stub width, the stub height being defined with reference to the reference plane of the side wall in which the resonant cavity is formed and the stub width corresponding to the opening of the resonant cavity on the waveguide channel. The filter according to one of the preceding claims, in which the resonant cavity has a height defined in a direction perpendicular to the reference plane of the side wall in which the resonant cavity is formed, the height being between 0.1 λ & 2 and 0.8λ & 2 , where λ & 2 is the guided wavelength corresponding to the center frequency of the rejected band B2. The filter according to one of the preceding claims, in which the opening of the resonant cavities on the waveguide channel is comprised between 0.08λ & ι and 0.35λ & 1, where λ & 1 is the guided wavelength corresponding to the central frequency of the band passerby Bl. The filter according to one of the preceding claims, wherein each resonator of the plurality of resonators comprises a step which is formed on the wall opposite the resonant cavity of the same resonator and which protrudes into the channel beyond the reference plane of the wall in which it is formed, each step facing a respective resonant cavity, the steps being arranged in a one-to-one correspondence with the respective resonant cavities. The filter of claim 7, wherein the resonant cavity has a width corresponding to the opening of the resonant cavity on the waveguide channel and the step opposite the resonant cavity has a step width along the direction of propagation of the signals substantially equal to the resonant cavity width. The filter of one of claims 7 or 8, wherein the step structure has a step height defined with reference to the reference plane of the side wall in which the step is formed, the step height being between 0 and 0.15λ & 1, where λ & 1 is the guided wavelength corresponding to the central frequency of the passband Bl. The filter according to one of the preceding claims, in which the electronic filter is a band reject filter in which each resonator has at least one transmission zero at a frequency included in the rejected band B2 and at least one reflection zero at a frequency included in the band passerby Bl. 11. A diplexer (60) which comprises a common access section (61) for the input of electromagnetic signals in the operating frequency band, a transmission filter section (63) and a receiving filter section (64), both filter sections being coupled to the common access section so as to receive the electromagnetic signals entering the common section, wherein each filter section is a filter according to one of the preceding claims. 12. A multiplexer comprising a common access section for the input of electromagnetic signals in the operating band of frequencies and a plurality of filter sections, each filter section being configured to separate a sub-band of frequencies comprised in the operating band and being coupled to the common access section, wherein at least one of the plurality of the filter sections is a filter according to one of claims 1 to 10.