US3550141A - Cavity slot antenna - Google Patents

Description

543-872 XR 3550141 5R Dec. 22, 1970 J, HARRIS ETAL 3,550,141

CAVITY SLOT ANTENNA Filed Feb. 5, 1969 2 Sheets-Sheet l VSWR=3.0=I 3 I800 mc BANDWIDTH VSWR=2.0=| 2 I I600 me 7 l BANDWIDTH o 1 VSWR o 1 o o 1 o 1 I -O--o-o 1 E l i 1 i i 1 l I N 1 j i 1 4 4 i I I 0 h i I i 40 5000' 5500 6000 6500 7000 FREQU ENCY (MEGACYCLES) John R. Harris John W. Tse Gerald H. Hooper INVENTORS %.o.| MM BY WWWM AGENT DQC. 22, 1970 HARRls ETAL 3,550,141

CAVITY SLOT ANTENNA Filed Feb. 5, 1969 2 Sheets-Sheet 2 States Patent US. Cl. 345-461 Claims ABSTRACT OF THE DISCLOSURE An antenna in which a pair of diametrically disposed and interconnected kidney-shaped slots in one end of a substantially] cylindrical housing forms a resonant cavity therein. dielectric window is secured to the end of the housing to cover the open cavity.

BACKGROUND OF THE INVENTION This invention generally relates to antenna structures and more: particularly to antennas of the cavity slot variety.

Heretofore, antennas of the wave guide, single slot, multiple slot, and wire or rod-types have been commonly used. wh re; limited space has been a prime factor, however, the p'revious antenna-s have been tuned inivan'ous ways, which correspondingly have limited their frequency bandwidths and gains. Among the most suitable antennas of the prior art are the flush-mounted, cavity slot types, wherein the. cavity design has been based on a foaming technique." The electrical properties of the polyurethane foam, however, are very sensitive to change in density and chemicalcomposition of the foam. It is evident therefore that different mixing and curing techniques and the size of the container to be foamed all affect the density, and thereby the electrical properties of 'the foam.

Such has" resulted in a high rejection rate of antennas of this type.

One of the major problems in the design of antennas adapted for use in aircraft or missiles is to meet the thermal reguirements. Due to the different thermal conductivitiesi'a'the heat flow problems are quite complex. For example, the external temperature of the cavitycould reach a very high temperature, and the performance of the antenna might be detuned if materials of low thermal conductivity areused. The internal portions of the antenna will of course be raised to very high temperatures,

regardless of the materials used.

. SUMMARY OF THE INVENTION It is, therefore, an object of this invention to provide an antenna having a substantially constant impedance over a wide frequency bandwith and a broadbeam radiation pattern. 3

Another object; of the present invention is the provision of a small and compact antennasuitable for flush mount installation on an aircraft or missile.

Yet another object of this'invention is the provision of an antenna comprised of a minimum number of parts and having a low manufacturing cost.

Still another object of this invention is to provide an antenna having high resistance to high voltage breakdown at very high altitudes.

Briefly, in accordance with our embodiment of the invention, the foregoing and other objects are attained by an antenna made up of only five basic parts and being suitably designed for flush mount installation. The parts of the antenna include a housing forming the cavity, a

- dielectric window covering the cavity, a retaining lock ring, a mounting flange and an RF connector.

many of its attendant advantages will be readily apparent as the same becomes better understood by reference to the detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a side cross-sectional view of one embodiment of this invention;

FIG. 2 is a cross-sectional view of the device taken along the line 2-2 of FIG. 1, showing internal construction of the antenna and particularly the novel shape" of the cavity formed therein;

FIG. 3 is a cross-sectional view of the device taken along the line 3-3 of FIG. 2;

FIG. 4 is a graphical illustration showing the variation of VSWR (voltage standing wave ratio) with frequency for a cavity antenna of the present invention; and

FIG. 5 is a graphic presentation of a typical radiation pattern for an antenna of the present invention taken for a roll plane cut.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now in greater detail to FIGS. 1 to 3 of the drawings, the antenna structure of the invention comprises a substantially cylindrical-shaped housing 10 of an electrically conductive metal, having formed therein a cavity made up of a pair of diametrically opposed kidneyshaped slots 12 and an interconnecting linear slot 14. An

axial bore 16 through housing 10 is positioned adjacent one side of the linear slot 14 and between adjacent ends of the kidney-shaped slots 12. At the end of the housing- 10 wherein the .cavity is formed, a slot 18 of the same width as the diameter of bore 16 and of less depth, connects the bore with the linear slot 14 and thereacross to certain super alloys of steel, or other metals exhibiting very high thermal conductivities. 7

It should be readily apparent that the depth of the cavity formed in housing 10 may be varied in accordance with the requirements of a particular application and frequency response desired.

A coaxial 50 ohm RF transmission line 22, having an inner conductor 24, is passed through the bore 16 in the housing 10 and is securely fastened there to be an RF connector 26. The inner conductor 24 is bent over the slot 18 and across the linear slot 14 of the cavity, and is press fitted or soldered into the narrow channel or receiving aperture 20.

A dielectric cover plate or window 28 is secured to the open end of housing 10, thereby protecting the cavity from intrusion of moisture or other foreign matter which could affect the tuning of the antenna. As more shown in FIG. 1 of the drawings, the window 28 is substantially disc-shaped in configuration to fit matingly against the end of housing 10 and is provided with an end face 30 of reduced diameter adapted to engage a flange 32 of a mounting shell 34. The shell 34 is exteriorly threaded at the flanged end thereof for attachment to the aircraft or missile and is interiorly threaded at the other end for engagement with .a lock ring 36. An end of lock ring 36 abuts a shoulder 38 formed on the circumferential wall of housing 10 when it is threaded into the mounting shell 34, and thereby secures the five basic elements of the antenna together.

The particular arrangement of the antenna cavity and Patented Dec. 22, 1970 H i I g 1. 1. l .1-2tilii. t-t'isiattm. feed lends itself to potting the cavity housing and .the window 28 simultaneously in a very simple fixture.

One approach found to be acceptable is using eccoceram, a ceramic potting compound of which there are two types. Their dielectric constants range from 2.8 to 3.6. After potting, this material will sustain continuous temperaturesto 2500 F.

Although many materials may be acceptable, the material from which the window 28 is constructed must be able to handle very high temperatures, such as those encountered during re-entry into our atmosphere of certain missiles. One such material is boron nitride.

If desired,the antenna may be hermetically sealed at atmospheric pressure to reduce high voltage breakdown at high altitude.

FIG. 4 is a typical data plotting for the embodiment of FIGS. 1-3, wherein voltage standing wave ratio (VSWR) is plotted as a function of frequency of the electromagnetic wave signal being radiated bythe antenna. It is readily evident from this characteristic curve that the frequency bandwidth and the impedance factor obtained with the antenna of this invention is much improved over that of conventional cavity antennas. Exemplary of this is the fact that a bandwidth of 1800 megacycles below a VSWR of 3.0 to 1 is achieved with the novel kidneyshaped cavity antenna of this invention.

Likewise, FIG. 5 is a graphic showing of the radiation pattern for the embodiment of FIGS. 1-3 taken for a roll plane cut. Here it may be observed that the antenna gain is 3.0 db above an isotropic radiator, and the beamwidth is 110 at the --3.() bd points.

Briefly stated in summary, according to the present invention, a compact cavity antenna designed for flush mount installation is provided having a substantially constant impedance over a wide frequency bandwidthand a broadbeam radiation pattern.

Obviously many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced 2. An antenna according to claim ll wherein said housing is constructed of beryllium.

3. An antenna according to claim 1 wherein said cover plate is constructed of boron nitride.

4. An antenna according to claim 1 wherein said energy introducing means is a transmission line extending into said housing between said kidney-shaped slots and adjacent said linear slot,

said line being bentover said linear slot and secured to said housing. 1 I

5. A wideband antenna structure according to claim 1 wherein said housing is substantially cylindrical-shaped and constructed'of beryllium, W

said cover plate is substantially disc-shaped and constructed of boron nitride, and

said energy introducing means is a transmission line extending into said housing from the end opposite said cover plate between said kidney-shaped slots and adjacent said linear slot,

said line being bent over said linear slot and secured on the opposite side thereof to the housing.

6. Ah antenna according to claim 1 wherein said housing and said cover plate are secured with a ceramic potting compound.

7. An antenna according to claim 1 wherein said cavity is hermetically sealed at atmospheric pressure.

8. An antenna according to claim 5 wherein said housing and said coverplate are secured with a ceramic potting compound, and

said cavity is hermetically sealed.

9. .An antenna according to claim 5 wherein said housing and said cover plate are connected by a tubular shell and a lock ring,

said lock ring and said shell enclosing said housing 'and said cover plate and being threadably secured to each other.

10. An antenna according to claim 9 wherein said housing and said cover plate are further secured with a ceramic potting compound, and

said cavity is hermetically sealed.

. References Cited UNITED STATES PATENTS 3,262,119 7/1966 Sisson 343771X ELI LIEBERMAN, Primary Examiner M. NUSSBAUM, Assistant Examiner us. 01. X.R.

Images