Cavity Excited Conical Dielectric Radiator

Abstract

Disclosed is a small, compact, efficient antenna that uses practically no ace and is employed on the tip of a projectile. The antenna is in the form of a nose cone body having an electrically conductive inner surface. The electrically coated inner surface extends around the base of the nose cone body and partially coats the outside of the nose cone and forms a band of conductive coating at the base thereof. The antenna is excited by a coaxial probe connected to the metal coating on the inside of the nose cone. Diametrically opposite the input for the coaxial probe a deep post is located across the cavity at its center in order to provide a short circuit. The excited antenna radiates along the tapered dielectric cone (the portion that is not coated) and couples to free space.

Description

RIGHTS OF THE GOVERNMENT

The invention described herein may be manufactured, used, and licensed by or for the U. S. Government for governmental purposes without the payment to the inventor of any royalty thereon.

BACKGROUND OF THE INVENTION

Heretofore separate antenna structures were incorporated into the body of a reentry vehicle to excite the vehicle body for radar or other applications. Other conventional structures for exciting missile bodies have generally employed stubs, monopoles, dipoles, and loops as radiating elements. However, apertures for the antennas and other discontinuities constructed into the surface of missile structures for these types of excitation elements often produce undesirable aerodynamic effects and changes in the missile radar cross-sectional area which can be extremely detrimental to the radiation pattern and to the operation of the missile system. One recent construction in the previous art provided a nose cone for a re-entry vehicle in which the excitation antenna was recessed and relocated at or near the base of the nose cone.

The present invention avoids the above mentioned difficulties by providing an antenna that uses practically no space and can be conventionally employed on the tip of a projectile and in which the excitation probe is inserted directly into the nose cone and provides no obstruction other than a coaxial input plug located on the inside thereof.

It is therefore one object of the present invention to provide a new and unique antenna which is small, compact, and efficient and occupies practically no space whatsoever.

Another object of the present invention is to provide an antenna which may be designed and fabricated onto existing projectile nose cone structures, consuming no additional space.

Another object of the present invention is to provide a unique antenna utilizing practically no space which possesses high efficiency and broad radiation coverage.

It is yet another additional object of this invention to provide a new and unique antenna design having low input impedance and good bandwidth at L band.

These and further objects and advantages of the invention will be more apparent upon reference to the following specification, claims, and appended drawings.

SUMMARY OF THE INVENTION

In accordance with this invention a new small, compact, and efficient antenna is provided which utilizes, in essence, no space and is conveniently employed on the surface of the nose cone of a projectile. The antenna is comprised of a coating of conductive material throughout the inside wall of a nose cone cavity, said conductive coating extending over the base of said nose cone and connecting a band of conductive coating extending uniformily around the base of said nose cone. A coaxial input to said conductive coating is provided and interconnected to the inside of said nose cone, diametrical to said coaxial input and centered within the borders of said outside conductive coating is provided a shorting post. The antenna is excited by interconnecting a matched coaxial probe into the coaxial input whereby microwave energy excites the antenna to radiate along the uncoated outside portion of the tapered dielectric cone and couple to free space.

BRIEF DESCRIPTION OF THE DRAWINGS

The specific nature of the invention as well as other objects, aspects, uses, and advantages thereof will clearly appear from the following descriptions and the accompanying drawings in which:

FIG. 1 is a perspective view of a preferred embodiment of the instant invention.

FIG. 2 shows the radiation pattern of a preferred embodiment of the antenna in accordance with this invention.

FIG. 3 is a graph of the voltage standing wave ratio of a cavity excited conical dielectric radiator as a function of frequency.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, FIG. 1 shows a preferred embodiment of the cavity excited conical dielectric radiator, generally indicated at 5, in the form of a conventional nose cone for the vehicle body having an electrically conductive metallic inner skin or coating 34, said coating 34 extending over the inside edge 33 of the nose cone and completely interconnecting a similar conductive coating 35 covering the base of the nose cone 10. Partially covering the outside of said nose cone generally at 5 is conductive coating or skin 30 which interconnects the coating 35 covering the base and extends from the outer edge 31 a distant L toward the tip of said nose cone. This outer coating 30 has a border or terminating edge 32 which extends completely around the nose cone.

The nose cone 10 is comprised of epoxy or other dielectric material suitable for the particular frequency to be utilized. A coaxial input connecter is connected to the inside conductive surface 34 of the dielectric radiator. Dimetrically opposite this coaxial input is located a shorting post 20. This shorting post extends through the dielectric nose cone 10 and connects the outer conductive coating 30 to the inner conductive coating 34.

One specific embodiment of the conical dielectrical radiator 5 is comprised of an epoxy fiberglass cone whose wall thickness is three-sixteenths of an inch having a base diameter of 21/4 inches and a height of 23/4 inches. The conductive metal coating of the cone is comprised of copper plating. In this embodiment of distant L is indicated in FIG. 1 is approximately 11/8 inches. The wall thickness specified is selected such that it optimally matches a 50 ohm input which is interconnected and juxtaposed to the inside wall. The coaxial probe used to excite the antenna is placed across the cavity at the proper position for maximum radiation.

This particular preferred embodiment of the antenna when mounted onto a weapon system provides a radiation pattern as shown in FIG. 2. This pattern Indicates that the entire body is excited and that the maximum energy is directed toward the rear of the nose cone. The peak gain is about 2.0 db above an isotropic radiator. This figure also shows that there is good radiation coverage about the body of the radiator with a minimum of radiation along the axis forward and rear. This particular preferred embodiment of the conical dielectric radiator is resonant at approximately 1.275 MHz. The voltage standing wave ratio or VSWR is 2.0 to 1.0 or less over 110 MHz as seen in FIG. 3.

It is noteworthy to specify that the design and construction techniques employed in the development and manufacture of this particular radiator are relatively simple. More so the overall fabrication cost is minimum in comparison to other state-of-the-art antenna designs.

Typically the conductive thin coatings for the radiator may be either copper, gold, silver, steel or platinum gold. The body itself may be made of either Teflon, epoxy, plastic, Fiberglas, or ceramic.

Referring again to the drawings, in FIG. 3 the radial lines such as represented by line 60 indicate relative power radiated in decibels or dB. And, the curve traced by line 63 is relative power as a function of elevation. The curve represented by line 62 is relative power as a function of azimuthal variation. The vector 61 represents the forward axis of the conical dielectric radiator.

It should be understood that the invention is not limited to the exact details of construction shown and described herein for obvious modifications will occur to a person skilled in the art.

Claims

I claim as my invention:

1. A cavity excited dielectric radiator comprising a body of dielectric matter having a outer surface and inner surface, said inner surface having a skin of conductive material affixed thereto, said outer surface having a partial covering of skin of similar conductive material, said skin on said outer surface being connected to said skin on said inner surface, and further comprising an electromagnetic energy input means affixed to said inner conductive skin and a shorting post imbedded in said dielectric matter and located diametrically opposite to said means wherein said shorting post connects said outer skin to said inner skin.

2. The radiator of claim 1 wherein said body of dielectric matter is a nose cone for a projectile, said cone having a base.

3. The radiator of claim 2 wherein said outer skin is a uniform band of conductive coating extending around said body and covering said body from said base to a distance L.

4. The radiator of claim 3 wherein said shorting post comprises a thin metal rod.

5. The radiator of claim 4 wherein said input means is a 50 ohm coaxial input connector.

6. The radiator of claim 3 wherein said shorting post is a conductive filling.

7. The radiator of claim 3 wherein said skins are extremely thin with respect to the wall thickness of said dielectric body.