CA1136267A

CA1136267A - Array of annular slots excited by radial waveguide modes

Info

Publication number: CA1136267A
Application number: CA000332541A
Authority: CA
Inventors: Bahman Azarbar; Lotsollah Shafai
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-07-25
Filing date: 1979-07-25
Publication date: 1982-11-23

Abstract

ABSTRACT OF THE DISCLOSURE
A high gain antenna suitable for use in satellite or similar communications systems having low profile, low weight and which does not interfere with dynamics during movement through space. The antenna has variable radiation patterns by the excitation of one or several radial modes. Basically the antenna is a simple radial open or closed waveguide with a slotted wall and transmission line to the radial waveguide at one or several places to launch the desired mixture of radial waveguides modes. The antenna may also be used as a filtering device in couplers and multi-feed systems.

Description

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This invention relates to an antenna of the annular slotted array type of particular, but not exclusive, use in satellite communication or similar communications.
Prior known antennas of the subject class are dis-closed in United States Patents 2,508,085, issued May 16, 1950 to Andrew Alford; 2,838,754, issued June 10, 1958 by Robert W. Bic~mere and assigned to The Regents of the Univer- ~`
sity of California, Berkeley, California; 2,977,595 issued - March 28, 1961 by Siegfried Zislter et al and assigned to Societe Francaise Sadlr-Carpentier and 4,032,921, issued June 28, 1977 by Thomas V. Sikina, Jr. et al and assigned to American Electronics Laboratories.
Patents 2,508,085 and 2,977,595 are slot antennas for which the slot is excited by a wire and are useful at low ~;
frequencies. Patent 4,032!921 is a spiral antenna wherein two slots are used to modify the spiral antenna characteristics - but no use is made of the surrounding and supporting structure.
These three prior patents will be shown to differ from the antenna of the subject proposal. Patent 2,838,754 is a complex device which uses a non-spiral slot array, backed by a slot array backed by a cylindrical cavity, which is necessary for the excitation of its internal modes. The surrounding and supporting structure plays no part in its operation and the cavity housing houses a complex filter to remove undesirable modes and the antenna uses many probes to excite its slots.
It is a feature of the present invention to provide a high gain, low cost high frequency antenna system.
It is a feature of the present invention to provide a high frequency antenna suitable for use in satelllte space-craft and all ground o~nunication~
It is a further ~eature to provide a high frequency ~ 362~

antenna of simple geometry, suitable for rapid production, and inexpensive to fabricate.
It is a further feature to provide a high frequency antenna of small overall size and of light weight.
It is yet another feature to provide a filtering device for use in couplers and multi-feed systems.
It is yet another feature to provide a high fre-quency antenna suitable for fabrication using printed circuit technologyO
It is another feature to provide a high frequency antenna capable of various radiation patterns and of high ;~
aperture efficiency. ~ `
In accordance with the foregoing objects, there is provided:
A high-gain, high-frequency radiator comprising a plurality of annular slots f~ormed in an outer conducting plate, said outer conducting plate belng separated from an inner ; ~
conducting plate by~a dielectric substrate thereby deining a ~ `
radial waveguide, means for connecting a transmission line to ~
at least one point on said outer conducting plate to launch "
radial waveguide modes, which in turn excite the slots.
A preferred embodiment of the invention will be described with reference to the accompanying drawings/ in which~
Fig. 1 is an isometric view of the basic radiator.
, FigsO 2(a) and 2(b) are the respective arrangements ~-of the annular slot array fed by a radial waveguide or cavity. -~
Fig~. 3(a) and 3(b) are similar to Figs. 2(a) and ~ -

2(b) but indicate, respectively, two symmetri`aa~lly oriented -~
probes and a waveguide to excite the radial waveguide modes.
Fig. 4 is a graph of the E and the H relative power

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patterns, one way, versus angle of the antenna system. ~ ~
Referring now to Fig. 1, there is shown a basic ~ -- radiating eleme~t 1 consisting of a pair of conductlng planes 10 and 12 formed on-and separatPd by a~dielectric substrate 14 An annular slot array is formed by concentric slots 16, 16B and 16C disposèd in the conducting plane 12. This arrangement forms a radial structure ~waveguide or cavity).
Radiation is through the array of slots and a high gain selec-tive radiation pattern in the direction of the slot axis is obtained by proper excitation o~ the radial modes. The slot configuration can also be modified to yield desired radiation charactexistics.
, Referring to Figs. 2(a) and 2(b), there is shown annular slot arrays fed by a radial waveguide or cavity. The conducting planes and slots have the same identification numer-?O als as in Fig. l.
In Fig. 2(a), the conducting planes are separated by a distance a and;the radial waveguide is not terminated, and the slots having a radiaL spacing of x. The innermost slot has radial distance Pl and the slots are ~ wide.
In Fi~. 2(b), structure is terminated at a radius C with a wall 20 to form a radial cavity ~hereby ensuring total radiation power to the external region. ;~
In Fig. 3(a) when a high gain in -the forward direc~
tion is desired two probes are excited with 180 phase differ-ence. When a n~ll in the forward dlrection is required, both probes are excited in phase. In Fig. 3(bj simllar radiation ' `` 1136Z~7 :`

patterns are obtained by exciting the proper modes of ths radial waveguide through the use of circular wave~uide feed.
In Fig. 4 the portions of the curves to the left of the 0 position are representative of the E-plane radiation pattern, and the portions to the right of the 0 position are representative of the H-plane radiation pattern. The curves with small cixcles thereon are theoretical while the other curves without such circles are the exp~r~mental ones.
It is to be understood that the embodiments thus far described can be modified to conorm to the geometry of the supporting structure, such as a satellite, spacecraft or any other stxucture. The antenna may include a relatively large encircling flange which overlays or forms part of the supporting structure. Such a flange can be used to control the edge dif-fracted power.
TMol de of the radial cavity is excited by two vertical probes. These probes are fed 180 degrees out of phase in order to cancel the dominant TMoo mode o the xadial struc-2~ ture and the feed system which may be a a~ial transmission line, islocated in the central region of ~e guiding medium. The T~l mcde of the anb~a ensures that the radiation is along the axis of the slots. When pn~s are excited in phase, the do~nant TMoo mDde radiates and the antenna patterns have a null in the forward direction. The antenna can also be excited directly, using a waveguid~ as shown in Fig. 3(b). `~

The antenna disclosed herein is a simple radial waveguide, wi~h slotted wall~ It does not need any probe to 3~

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excite its slots individually, it does not need any filter to remove the undesirable modes. Antenna field is excited by simply connecting the tra~smission line or a waveguide to the radial waveguide to launch the radial waveguide modes. It is the radial wa~eguide ~hat excites the slotsO The radial wave-guide may be open or closed (cavi~y or match terminated), whlchever is desirable.
The antenna can be fabricated by any standard method. ~`
However, its simple geometry yields itsel~ to rapid, low cost ``
fabrication using printed circuit technology. Such a technique ensures low cost fabrication due to minimal use of conductiny and dielectric materials, automation and simplicity of the geometry. Furthermore, high fabxicating accuracy is achieva~le which ensures exact duplication of the design.

Other embodiments falling within the ~erms of the appended claims will occur to those skilled in the art.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A high-gain high frequency radiator comprising a plurality of annular slots formed in an outer conducting plate, said outer conducting plate being separated from an inner conducting plate by a dielectric substrate thereby defining a radial waveguide, means for connecting a transmission line to at least one point on said outer conducting plate to launch radial waveguide modes which in turn excite the slots.

2. A high-gain high frequency radiator as defined in Claim 1 wherein said radial waveguide is unterminated.

3. A high-gain high frequency radiator as defined in Claim 1 wherein said radial waveguide is terminated by a wall extending between said inner and outer plates to define a radial cavity.

4. A high-gain high frequency radiator as defined in Claim 3 wherein said wall is a hollow cylindrical member.

5. A high-gain high frequency radiator comprising an outer conducting plate having a plurality of annular slots therein, an inner conducting plate, a continuous solid di-electric substrate separating said outer conducting plate from said inner conducting plate thereby defining a radial waveguide, said continuous solid dielectric substrate extending across said plurality of slots, and means for connecting a transmission line to at least one point on said inner conducting plate to launch radial waveguide modes which excite the slots.

6. A high-gain high frequency radiator as defined in Claim 5 wherein said annular slots are concentric.

7. A high-gain high frequency radiator as defined in Claim 5 wherein said radial waveguide is unterminated.

8. A high-gain high frequency radiator as defined in Claim 5 wherein said radial waveguide is terminated by a wall extending between said inner and outer plates to define a radial cavity.

9. A high-gain high frequency radiator as defined in Claim 8 wherein said wall is a hollow cylindrical member.

10. A high-gain high frequency radiator as defined in Claim 6 in which said means for connecting a transmission line comprises a coaxial line which divides into two branch lines which are connected to spaced points on the inner plate, the outer conductors of the branch lines being conductively connected to the inner plate, two probes in said radial wave-guide, the central conductor of each of the said branch lines extending through an aperture in said inner plate and being conductively connected to a separate one of said probes.

11. A high-gain high frequency radiator as defined in Claim 10 where m the probes are fed by signals 180 degrees out of phase, whereby the dominant TM00 mode is cancelled.

12. A high-gain high frequency radiator as defined in Claim 10 wherein the probes are fed by signals in phase.

13. A high-gain high frequency radiator as defined in Claim 6 wherein said means for connecting a transmission line comprises a circular waveguide.

14. A high-gain high frequency radiator as defined in Claim 5 in which said radial waveguide has a matched termination.