JPH02131601A - Microwave filter - Google Patents

Abstract

PURPOSE:To reduce a filter radiation loss due to the radiation from an open end of a parallel coupling line and to reduce the insertion loss of a filter in a pass band of a high frequency signal as a result by providing each parallel coupling line in parallel with a main line and in distribution coupling. CONSTITUTION:Parallel coupling lines 14, 15, 16, 17 are provided in parallel with a main line 13 in distribution coupling. The lengths l2, l3, l3, l2 of the parallel coupling lines 14, 15, 16, 17 are selected to be 1/4 wavelength or nearly 1/4 wavelength of an image signal so that the attenuation pole comes in the bond or in the vicinity of the band of the image signal. Then, the lengths l2, l3, l3, l2 of the parallel coupling lines 14, 15, 16, 17 and intervals l0, l1, l0 are selected so as to satisfy the condition of l1<l3<l2<l0<2l3. Moreover, the characteristic impedance of the parallel coupling lines 15, 16 whose attenuation pole comes near the pass band of a high frequency signal is set higher than the characteristic impedance of input and output line 18, 19.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a microwave filter using a strip line or a microstrip line. This relates to the configuration of a microwave filter when the bandwidth is finite.

Conventional technology A high frequency signal (frequency is fs) and a local oscillation signal (frequency is fl) having a different frequency from this signal are input, and an intermediate frequency signal (frequency is fsfl-) which is the frequency component of the difference between these two signals is input. However, in a mixer that outputs fs>fl as an output, the high-frequency signal is passed through the main line that transmits the high-frequency signal to the mixer diode without loss, but the high-frequency signal from twice the frequency of the local oscillation signal (2fl) is passed through the main line that transmits the high-frequency signal to the mixer diode. The frequency (2f) obtained by subtracting the frequency (f8) of
g-f8 ) image signal (frequency/m=21g
fs ) is provided with a blocking filter (hereinafter referred to as "signal passing/image blocking filter"), and furthermore, a local band pass filter (hereinafter referred to as "signal passing/image blocking filter") is provided between the local oscillation signal input terminal and the mixer diode to selectively pass only the local oscillation signal. "
A locally sourced BPFJ (abbreviated as local BPFJ) is provided. When a high frequency signal and a local oscillation signal are applied to a mixer diode, which is a nonlinear element, the frequency becomes w+f, ±n/gcm, where n is an integer)
wave measurement band and harmonics are generated. Then, among those spectra, the image signal frequency fta and the sum frequency 18+
Since the fg wave contains high-frequency signal components, the image signal in particular of these waves is returned to the mixer diode with a signal pass/image rejection filter and mixed with the local oscillation signal again to be reconverted. It is possible to obtain a high-frequency intermediate frequency signal, and as a result, the conversion loss of the mixer can be reduced. Furthermore, the interference wave signal having the same frequency as the image signal frequency enters from the high frequency signal input terminal and enters the intermediate frequency signal frequency band.
It can be blocked by a signal passing/image blocking filter.

In particular, in the case of a single mixer in which only one mixer diode is used, the mixer performance is greatly influenced by how the image signal generated by the mixer diode is processed. Usually, the impedance seen from the mixer diode terminal is set to be reactive with respect to the image signal frequency. Therefore, a signal pass/image rejection filter and a local BPF for suppressing image signals are essential components in constructing a single mixer. Since the signal pass/image block filter is provided on the main line that transmits the high frequency signal to the mixer diode or is coupled to the main line, the characteristics of the signal pass/image block filter directly affect the mixer performance. In other words, mixer performance is determined by the characteristics of the signal passing and image blocking filters. It is no exaggeration to say that there is.

Such a signal passing/image blocking filter is required to have the following performance.

(1) Insertion loss for high frequency signals should be as small as possible.

(2) It must have characteristics that sufficiently suppress image signals.

《Phrase: Must have the necessary passband width and stopband width for high frequency signals and image signals.

<<4> The closer the high-frequency signal frequency and the image signal frequency are, the more steep the out-of-band characteristics will be.

Conventionally, as a signal passing/image blocking filter used in a mixer, there has been one described in Japanese Patent Publication No. 10601/1983. The signal passing/image blocking filter described in the publication is shown in FIG.

In FIG. 6, an input terminal 1 and an output terminal 2 of a high frequency signal are connected by a main line 3 composed of a strip line, and the main line 3 has lengths l, . e2. The terminal open end taps 4, 5.6 of e, are successively connected in parallel at equal intervals with an interval lo. Open end stuff 4, 6, e (7)
The length sa (1, . 6 long sa l, .l2./!,
Interval 1. hag2<e,<l.

<2e2 and l2<l, <e. Either the condition 2l2 is satisfied or e2<E,=l! ,<1l. <2/! 2
At the same time, the length of ffo is selected to be approximately 1.6 times the A wavelength of the high frequency signal.

7.8 is an input/output line connected to the input/output terminal 1.2.

Problems to be Solved by the Invention The conventional signal passing/image blocking filter in which the terminal open tabs 4, 5 and 6 protrude perpendicularly to the main line 3 has the following drawbacks.

(1) Since the open termination studs 4, 6.6 are provided so as to protrude perpendicularly to the main line 3, radiation occurs easily and insertion loss within the passband of the high frequency signal becomes large.

(2) Since the attenuation pole of the open-ended tap 6 is on the higher side compared to other open-ended taps 4.6, by increasing the characteristic impedance of the open-ended tap 6, a filter characteristic with a relatively steep rise characteristic can be obtained. However, since there is only one open-ended tap with an attenuation pole on the Takagi side, a filter with a steep rise characteristic cannot be obtained.

(3) Since the terminal opening studs 4, 5, and 6 are provided so as to protrude in the direction perpendicular to the main line 3, the width of the filter becomes wide and the filter size becomes large.

The present invention has been made in view of these points, and an object of the present invention is to provide a microwave filter that has low insertion loss due to radiation within the passband of a high frequency signal, has a steep rise characteristic, and is small in size.

Means for Solving the Problems In order to solve the above problems, the microwave filter of the present invention has a main line having an input terminal and an output terminal, and an ffo. A'+. no' (however, go; lo')
The first . Second. a third and a fourth parallel coupled line, and the first... Second. The third and fourth parallel coupled lines each have lengths e2.13.1,' . 1!2'
are distributively coupled to and parallel to the raw line, and have lengths e2,1, . 1,'. /l2'
is chosen to be the length of the wavelength of the stopband frequency so that the attenuation pole is within the stopband, and e1<(l3cut l,')
<(g2 cutlet l2')<(eo cutlet eo')<(2g,
Ruka that satisfies the condition 2e3'), or ll, <
l, - 1,'<l2=l2'<lo=lo'
40. so as to satisfy the condition <(2l, and 2l,'). "O""'I"2"'2"Is'('S'
It is characterized by the selected length.

Further, in the microwave filter of the present invention, the first parallel coupled line and the second parallel coupled line are opposed to the main line, and the third parallel coupled line and the fourth parallel coupled line are arranged to face the main line. The first type is characterized by facing the line, or the first type has an open end. Second. 3rd and 4th
The characteristic impedance of the parallel coupled line is selected to be higher than the characteristic impedance of the input/output line connected to the input terminal or the output terminal.

According to the present invention, since each parallel coupled line is provided parallel to the main line and distributedly coupled, it is possible to reduce the radiation loss of the filter due to radiation from the open end of the parallel coupled line. As a result, the insertion loss of the filter can be reduced within the passband of the high frequency signal, and the amount of attenuation of the filter can be increased within the stopband of the image signal.

In addition, by setting the characteristic impedance of the parallel coupled line whose attenuation pole is close to the pass band of the high frequency signal to be higher than the characteristic impedance of the input/output line, the Q value within the stopband of the parallel coupled line becomes high. Moreover, since the attenuation pole is constituted by two parallel coupled wires, a filter characteristic with a steep rise characteristic can be obtained.

Further, since the parallel coupling line is provided parallel to the main line in a distributed manner, the width of the entire filter becomes narrower, and the filter dimensions become smaller.

Embodiment FIG. 1 shows a signal passing/image rejection filter according to the first embodiment of the present invention, in which the input terminal 11 and output terminal 12 of high frequency signals are connected to a main line 13 composed of a strip line.
The length of each knot is l! 2.1,. (1,.tl2
Parallel coupled lines 14.15, 16.17 with open ends are provided parallel to the main line 13 and distributedly coupled to the main line 13 and the parallel coupled line 14.1! , 16.17 are the intervals l, respectively. ．． l,. It is connected to the main line 13 at the go point. Length of parallel coupled lines 14.15, 16.17 62. (Is .is .g2 is selected to have a length of A wavelength or approximately μ wavelength of the image signal so that the attenuation pole is within or near the band of the image signal.Then, the parallel coupling line ii31 4 , 1 6 , 16 . 1
7 (D length 112-125.15.142 and interval l
. ．． l,. lo is l, <l, <l2<l. <21, and at the same time, the length of tla is selected to be around 1.6 times the apparent wavelength of the high frequency signal, and the length of l is selected to be 0.6 to 1 times the wavelength A of the high frequency signal. I choose around .0 times. Moreover, the characteristic impedance of the parallel coupled circuits 15, 16 whose attenuation poles are on the high side of the image signal, that is, on the side close to the high frequency signal, is the characteristic impedance of the input/output line 18, 19 connected to the input/output terminal 11, 12 ( Usually 6
0Ω).

In this embodiment, since the parallel coupled lines 14.1B and 16.17 are provided in parallel with the main line 13 and distributedly coupled, radiation from the open ends of the parallel coupled lines 14, 16, 16.17 is As a result, the insertion loss of the filter can be reduced within the pass band of the high frequency Nobuhide, and the attenuation amount of the filter can be increased within the stop band of the image signal.

Furthermore, since the characteristic impedance of the parallel coupled line 15.16 whose attenuation pole is close to the pass band of the high frequency signal is set higher than the characteristic impedance of the input/output line 18.19, the parallel coupled line 16.16 Since the Q value within the stop band becomes high and the attenuation pole is constituted by two parallel coupled lines 15 and 16, a filter characteristic with a steep rise characteristic can be obtained. In addition, parallel coupled line 1
4.16, 16.17 are provided in parallel with the main line 13 and distributedly coupled, so the width of the entire filter is narrowed and the filter dimensions are reduced.

FIG. 2 shows a signal passing/image blocking filter according to a second embodiment of the present invention, in which a high frequency signal input terminal 21 and output terminal 22 are connected to a main line circuit 23 composed of a strip line.
and each length is (12.Is-11s-112
Parallel coupled wire circuits 24, 25, 26, 27 with open ends are provided parallel to the main line 23 and distributedly coupled to the main line 23 and the parallel coupled lines 24, 24, . 25, 26. 27 is the interval e. ．． e,. It is connected to the main line 23 at a distance of ljo. Moreover, the parallel coupled shunt path 26 is arranged such that the parallel coupled lines 24 and 26 face the main line 23.
and 27 are configured to face the main line 23K. Length LJ's. of parallel coupled lines 24.26, 26.27. #s. #2 is selected to be the A wavelength or approximately the A wavelength of the image signal so that the attenuation pole is within or near the band of the image signal, and the length of the parallel coupled lines 24, 25, 26, and 27 (f2 .1!,.1,
．． 112 intervals 11. ．． 1,. 1! o is 11, <
l,<l2<l! . <2l, and at the same time, the length of lo is selected to be 1.0% of the wavelength of the high frequency signal.
Select around 6 times, and the length of l is 0% of the wavelength of the high frequency signal.
．． I choose around 5 to 1.0 times. Moreover, the characteristic impedance of the parallel coupled line 25.28 whose attenuation pole is on the high side of the image signal, that is, on the side close to the high frequency signal, is the characteristic impedance of the human output line 28.29 connected to the input/output terminal 21.22 (usually 60Ω). ).

Figure 3 shows the dielectric constant of the dielectric substrate for IJ drop line is 2.6, the thickness is 0.6RM, and the characteristic impedance of parallel coupling @ approximately 24, 26, 26.27. 120Ω, input/output line 28. The characteristic impedance of 29 is 60Ω, /o :6,6fl,g+ =2
j3fl, l2=5.5ff, l, =6.28
This shows the filter characteristics when however,
Parallel coupled lines 24 , 25 , 26 . An edge capacitance occurs at the open end of 27 due to an edge effect, and calculations are made taking this edge capacitance effect into consideration. In the filter shown in Figure 3, VS
WR is 1.4 or less, 9.6 to 10.6 GHz
A characteristic having an attenuation amount of 30 dB or more has been obtained in the frequency range of . Therefore, in a filter having the characteristics shown in Fig. 3, the high frequency signal is in the frequency range of 12.1 to 140 GHz, and the image signal is in the frequency range of 9.6 to 10.6 GHz.
This sufficiently satisfies the performance required as a signal passing/image blocking filter for mixers in the Hz frequency range.

Moreover, since the filter's component is only parallel coupled lines, its dimensions are small and the insertion loss for high-frequency signals is extremely low.It suppresses image signals and allows high-frequency signals to pass through without loss. It is particularly effective as a filter.

In this embodiment, the parallel coupled lines 24, 26, 26, . 2
It is possible to reduce the radiation loss of the filter due to radiation from the open end of 7, and as a result, the insertion loss of the filter is reduced within the pass band of the high frequency signal, and the amount of attenuation of the filter is increased within the stop band of the image signal. can be done. In addition, a parallel coupled line 26. whose attenuation pole is closer to the pass band of the high frequency signal. The characteristic impedance of 26 is the input/output line 28 . Since the characteristic impedance of 26.29 is selected to be higher than that of 26.
Since the Q value within the stop band of 26 is high and the attenuation pole is constituted by two parallel coupled lines 26, 26, a filter characteristic with a steep rise characteristic can be obtained. In addition, the parallel coupled lines 24, 25, 26, 27 are distributed parallel to the main line 23 and coupled in a distributed manner. 27 are mutually main line 2
Since it is configured to face 3, the width of the entire filter. The length is shortened and the filter dimensions become very small.

FIG. 4 shows a signal passing/image blocking filter according to a third embodiment of the present invention, in which a high frequency signal input terminal 31 and output terminal 32 are connected to a main line 33 composed of a strip line.
with an open end stud 34. of length l2. 37 is connected in parallel to the main line 33, and the parallel coupled line 35 has a length of e.
．． 36 is provided parallel to the main line 33 and distributedly coupled to it, and the main line 33 and the terminal open tap 34, the parallel coupled line 36, 36, and the terminal open tab 37 are each spaced apart from each other by a distance e.
．． ．． e. ．． l. It is connected after Length e2 of the open end studs 34, 37 and parallel coupled line 35.
The length e of 36 is selected to be the μ wavelength or approximately the IA wavelength of the image signal so that the attenuation pole is within or near the band of the image signal. and open end stub 34
, 37 length e2, parallel coupled line 35.36 length e
, and their spacing 11 o . e + - 14
o ha l + <11 s <11 2 < 1! o
< 211 s, and at the same time select l. The length of g is selected to be approximately 1.6 times the % wavelength of the high frequency signal, and the length of g is selected to be approximately 0.6 to 1.0 times the wavelength A of the high frequency signal.

Moreover, the characteristic impedance of the parallel coupled line 36.36 whose attenuation pole is on the high side of the image signal, that is, on the side close to the high frequency signal, is the characteristic impedance of the input/output line 38.39 of the filter connected to the input/output terminal 31.32. (usually 60Ω).

In this embodiment, the parallel coupled lines 35.36 whose attenuation poles are closer to the high frequency signal are provided in parallel with the royal wire 33 and distributedly coupled, so the parallel coupled lines 35.3
It is possible to reduce the radiation loss of the filter due to radiation from the open end of the filter, and as a result, the d
The insertion loss of the filter within the subband can be reduced.

Further, the characteristic impedance of the parallel coupled lines 36, 38 whose attenuation poles are close to the pass band of the high frequency signal is that of the input/output lines 38, 38 of the filter. Since the characteristic impedance of the parallel coupled lines 35.39 is set higher than that of the parallel coupled lines 35.39, the Q value within the stop band of the parallel coupled lines 35. 36, a filter characteristic with a steep rise characteristic can be obtained.

In addition, the parallel coupled line 36. By using 36, the size of the entire filter can be reduced.

In each of the embodiments described above, the filter configurations are all symmetrical. For example, in FIG. 1, parallel coupled lines 14 and 17 have equal line lengths of 1!2, parallel coupled lines 16 and 16 have equal line lengths of l, and further, parallel coupled lines 14 and 16 have equal line lengths of 1!
and the distance between the parallel coupled lines 16 and 17 are both g. are chosen to be equal, but those 7
It is not necessary that the lengths and intervals of the glands be exactly equal; if the line lengths are approximately equal and the intervals are approximately equal, the filter characteristics will not differ greatly from those in the case where the line lengths are equal and the intervals are equal.

Furthermore, the interval lo between open-ended lines and open-terminated taps is chosen to be longer than 6/16 wavelength of the passband frequency (or high frequency signal) < shorter than 7/16 wavelength, and the interval l is chosen as longer than the lA wavelength of the range frequency〈
If the wavelength is selected to be shorter than 2/8 wavelength, a filter with particularly excellent characteristics can be constructed, and the filter having the characteristics shown in FIG. 3 has filter dimensions that satisfy this condition.

Effect of the invention As described above, the present invention has the following effects.

(1) The parallel coupled line whose attenuation pole is on the higher side of the image signal, that is, on the side closer to the high frequency signal, is installed parallel to the main line and in a distributed manner, so that the parallel coupled line from the open end of the parallel coupled line Insertion loss due to radiation can be reduced within the passband of high frequency signals.

[a] The characteristic impedance of the parallel coupled line whose attenuation pole is close to the passband of the high-frequency signal is selected to be higher than the characteristic impedance of the input/output line of the filter (usually 60Ω), so it is within the stop band of the parallel coupled line. Since the Q value is high and the attenuation pole is constituted by two parallel coupled lines, a filter with a steep rise characteristic can be obtained.

(3) Length of parallel coupled line or open-ended stub 12
, ls are selected to be the A wavelength or almost the extreme wavelength of the image signal so that the attenuation pole is within or near the band of the image signal, and the length of the parallel coupled line or open-ended tap is 12. (Is and interval g..e,
is e, <14, <l! 2<l! By selecting such a condition that o<21, the following condition is satisfied, the rise characteristic becomes even steeper, and a filter characteristic with a wide passband width can be obtained.

(4) In particular, in filters consisting only of parallel coupled lines, the parallel coupled lines are provided parallel to the main line and distributedly coupled, so the overall width of the filter can be made very narrow, resulting in filter dimensions. can be made smaller.

[Brief explanation of drawings]

FIG. 1 is a pattern diagram showing a microwave filter circuit composed of strip lines according to the first embodiment of the present invention, and FIG. 2 is a pattern diagram showing a microwave filter circuit composed of strip lines according to the second embodiment of the present invention. FIG. 3 is a pattern diagram showing a specific example of the frequency characteristics of insertion loss of the filter circuit of FIG. 2, and FIG. 4 is a pattern diagram showing a microwave filter circuit of the present invention.
Figure 6 is a pattern diagram showing a microwave filter circuit composed of IJ strip lines. Fig. 6 is a pattern diagram of a microwave filter circuit composed of conventional strip lines. 11, 21. 31... Input terminal, 1 2 .
22. 32...Output terminal, 13, 23.33
...Main line, 14, 15, 16, 17, 24,
26, 26, 27. 35. 36...Parallel coupled line, 34.37...Open terminal stub. Name of substitute: Benkonshi Shigetaka Awano and 1 other person

Claims (5)

[Claims] (1) A main line with an input terminal and an output terminal, and l_0, l_1, l_0' (however, l_0≒l
The first, second, third and fourth parallel coupled lines each having an open end are connected in sequence at intervals of _0'), and the first, second, third and fourth parallel coupled lines are The lengths of the parallel coupled lines are l_2, l_3, l_3′, respectively.
l_2', distributed and coupled to the main line and provided in parallel thereto, with lengths l_2, l_3, l_3'
, l_2' are selected to have a length of 1/4 wavelength of the stopband frequency so that the attenuation pole is within the stopband, and l_1<(l
_3 and l_3') < (l_2 and l_2') < (l_
0 and l_0') < (2l_3 and 2l_3'), or l_1<l_3≒l_3'<l
_2≒l_2′<l_0≒l_0′<(2l_3 and 2
l_0, l_0', so as to satisfy the condition of l_3')
A microwave filter characterized in that the lengths of l_1, l_2, l_2', l_3, and l_3' are selected. (2) The first parallel coupled line and the second parallel coupled line face the main line, and the third line and the fourth parallel coupled line face the main line. The microwave filter according to claim 1, characterized in that: (3) The characteristic impedance of the first, second, third, and fourth parallel coupled lines with open ends is selected to be higher than the characteristic impedance of the input/output line connected to the input terminal or the output terminal. The microwave filter according to claim 1. (4) A main line with an input terminal and an output terminal, and l_0, l_1, l_0'' on this main line (however, l_0≒
It consists of first, second, third and fourth lines with open ends of lengths l_2, l_3, l_3', l_2', each of which is connected in sequence at one end at an interval of l_0'). The first and fourth lines are configured with open-ended stubs installed in parallel to the main line, and the second and third lines are configured with open-ended stubs installed in parallel to the main line for distributed coupling with the main line. It is composed of parallel coupled lines, and the lengths of the first, second, third and fourth lines are l_2, l_3, l_3',
l_2' is selected to have a length of 1/4 wavelength of the stopband frequency so that the attenuation pole is within the stopband, and l_1<(l_3 and l
_3') < (l_2 and l_2') < (2l_3 and 2
l_3') or l_1<l_
3≒l_3′<l_2≒l_2′<(2l_3 and 2l
l_0, l_0', l so as to satisfy the condition of _3')
A microwave filter characterized in that the lengths of _1, l_2, l_2', l_3, and l_3' are selected. (5) A claim characterized in that the characteristic impedance of the first, second, third, and fourth lines with open ends is selected to be higher than the characteristic impedance of the input/output line connected to the input terminal or the output terminal. 4. The microwave filter according to 4.