Monolithic, electrically small, multi-frequency antenna

Abstract

A projectile having a telemetry system built in which requires an antenna ich is structurally incorporated into the nose cone of the projectile. A dielectric material shaped to conform to the nose cone of the projectile is adapted to be part of the projectile exterior wall structure. A thin metallic coating is deposited on the entire inside surface of the dielectric nose cone and the coating is extended to cover a portion of the outside surface such as to leave the tip of the nose cone exposed, thereby defining an open end dielectric loaded radiator. A slot shaped aperture is provided in the coating and is located at the base of the nose cone so as to expose a portion of the dielectric and thereby define a slotted dielectric loaded cavity. A plurality of metallic coated holes are located circumferentially around the nose cone so as to electrically separate the open ended dielectric loaded radiator from the slotted dielectric loaded cavity. The resultant product is a multi-frequency, monolithic conical dielectric loaded cavity antenna.

Government Interests

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

Description

BACKGROUND OF THE INVENTION

Since the advent of projectiles utilizing proximity fuzing systems, telemetry, missile guidance, and other types of electronic communications, a problem in the design of such systems has been to provide an antenna which is small, compact and will not take up too much space within the projectile. This is especially important where the projectile has a fixed size and where space and weight limitations are critical problems in the design of self-contained fuzing and telemetry systems. Another problem has been to construct antennas in small diameter bodies which can handle signals at the lower microwave frequencies (800 to 2,500 mHz.) and which would lend themselves to multi-elements construction. It is also important that the electrical characteristics of these antennas meet design specifications. This normally means that the antenna must have certain specified radiation pattern characteristics, impedance matching and sufficient bandwidth and gain to fulfill the telemetry function.

Prior systems have utilized small antennas which are usually mounted in the nose structure of the projectile. These antennas used in prior systems normally utilized radiation elements such as loops, stubs and ring networks that were enclosed by the dielectric nose cone or body of the projectile. These elements have proven to be less efficient and more difficult to design and construct, and also far more costly to produce than is desirable for such systems. While many of the electrical characteristics desired could have been obtained with the use of cavity wave guide antennas, these antennas could not be used because of their extremely large size and heavy weight which has been inherent in the design of such systems. It is, therefore, an object of this invention to provide a projectile with an antenna system that uses a minimum of space within the projectile.

It is another object of this invention to provide a small, compact antenna system for a projectile which is efficient in its electrical characteristics and yet is extremely lightweight.

Still another object of the invention is to provide an antenna for a projectile which can be incorporated as part of the nose cone structure of the projectile.

Yet another object of the invention is to provide an antenna system for projectiles which can be easily constructed and is inexpensive to manufacture.

An additional object of the invention is to provide a new and unique antenna design having low input impedance and good bandwidth.

A further object of this invention is to provide an antenna design having multi-frequency design capabilities with good electrical isolation.

Yet another object of this invention is to provide an antenna design which reduces rf leakage to the other electronic components within the nose cone.

These and other objects and advantages of the invention will become more apparent with reference to the following specification, drawings and appended claims.

SUMMARY OF THE INVENTION

Briefly, in accordance with this invention, a projectile is provided having a telemetry system which is built entirely into the nose cone structure. A dielectric material shaped to conform to the nose cone of the projectile is adapted to be part of the exterior wall of the projectile. The dielectrical material is provided with a metallic coating deposited so as to cover the entire inside surface of the nose cone and to extend so as to cover a portion of an outside surface. The tip of the dielectric nose cone structure remains exposed so as to define an open end dielectric loaded radiator. A slot shaped aperture is provided at the base of the nose cone in the form of an exposed portion of the dielectric material and this defines a slotted dielectric loaded cavity. A plurality of metallic coated holes located in the metallic coated portion of the nose cone and circumferentially disposed around the nose cone provide an electrical separation between the open end dielectric loaded radiator and the slotted dielectric loaded cavity.

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 description and from the accompanying drawings in which:

FIG. 1 is a perspective view of the nose cone of a projectile in accordance with this invention;

FIG. 2 illustrates an inside view of the nose cone of FIG. 1.

FIG. 3 illustrates the radiation patterns of the open ended cavity section of the antenna in accordance with the present invention; and

FIG. 4 illustrates the radiation patterns of a single cavity in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, nose cone 10 consists of a dielectric material such as epoxy fiberglas 12. The dielectric material is provided with a metallic coating 13 which covers the entire inside of the nose cone and extends over the edge 14 and onto the exterior surface 11 of the nose cone. This coating is typically in the form of a copper plated surface which is coated on the dielectric material by means of a conventional electroless plating technique.

The base portion of nose cone 10 is provided with two radiating slots 15 and 16 which constitute a dual dielectric loaded cavity witih circumferential radiating slots. These slots simply constitute etched or exposed portions of the dielectric material 12. Each section of the dual cavity has its maximum radiating field normal to the axis of the cone and is fed from a coaxially input connector 21 and 22. If desired, both cavities can be fed from a common source and phased in such a manner as to get maximum radiation off the side or along the axis of the cone. Associated with each coaxially input feed is a shorting post 18 and 19. This shorting post extends through the dielectric material and connects the outer conductive coating 11 with the inner conductive coating 13. The two shorting posts thereby distinguish and define the two separate slotted dielectric loaded cavities.

At the forward end or apex of nose cone 10 is the open ended dielectric cavity which radiates surface waves through the exposed dielectric 12 into free space. This portion of the antenna has its maximum radiation normal to the axis of the nose cone, with nodes along the axis. Again a coaxially input feed 26 (see FIG. 2) is provided in the upper half of the nose cone and associated therewith a shorting post 20 is located diametrically opposed thereto.

A plurality of closely spaced copper plated holes 17 are disposed circumferentially in the plated portion of the nose cone. These closely spaced holes form a conducting barrier which electrically separates the open end dielectric loaded radiator located at the tip of the nose cone from the dual slotted dielectric loaded cavity located at the base of the nose cone. Of course, it is possible to replace the plurality of closely spaced holes with a single exposed ring or slot of dielectric material.

The typical nose cone size of the present invention is 3 inches high with a 2 inch base diameter. The dielectric materials from which the nose cone is made have a wall thickness of approximately three-sixteenths inch and a dielectric constant of about 4. The antenna has a low input impedance, about a 5 percent bandwidth where the VSWR is 2.0, and operates in the low S-band region. The radiation pattern of this portion of the antenna is shown in FIG. 3. The radiation pattern of one section of the dual cavity antenna, located at the base of the cone, is illustrated in FIG. 4. These radiation patterns and measurements were taken with the antenna assembly mounted on a cyclindrical body structure. It is, of course, possible to have other designs of this multi-frequency antenna. For example, the dual cavity could be a single cavity, designed to operate at a much lower frquency. Also, ther are many choices of dielectric materials which can be used that would change the operating frequency and vary the performance. Other designs utilizing a ridge incorporated in the cavity will change the frequency and bandwidth as desired. The conductive coating can be made out of copper, gold, silver, steel or platinum. The dielectric materials can typically be made out of epoxy fiberglass, teflon, plastic or ceramic.

It will be appreciated that the antenna described herein eliminates many of the problems and difficulties that plagued prior art systems. A multi-frequency operating antenna system has been designed which is of a one piece integrated construction, is rigidly small and is provided with good electrical isolation. Because the dielectric material is fully plated on the inside, rf leakage to other circuits and components is materially reduced. The system requires no additional space and permits the inside of the nose cone to be utilized for other purposes.

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 persons skilled in the art.

Claims

I claim as my invention:

1. In the projectile of the class wherein a signal is generated within a projectile to be transmitted from an antenna, the improvement comprising:

a. a dielectric material shaped to conform to the nose cone of said projectile and adapted to be part of its exterior wall structure;

b. a metallic coating deposited on the inside surface of said dielectric and extending to cover a portion of the outside surface so as to leave the tip of said nose cone exposed to define an open end dielectric loaded radiator;

c. a slot shaped aperture in said coating located at the base of said nose cone to expose a portion of said dielectric and thereby define a slotted dielectric loaded cavity; and

d. a plurality of metallic coated holes in the metallic coated portion of said nose cone circumferentially disposed to electrically separate the open end dielectric loaded radiator from the slotted dielectric loaded cavity.

2. The invention defined in claim 1 further comprising means for connecting an input signal to said open end dielectric loaded radiator, and means for connecting a separate input signal to said slotted dielectric loaded cavity.

3. The invention defined in claim 2 further comprising a second slot shaped aperture to define a second slotted dielectric loaded cavity, and means for connecting an input signal thereto.

4. The invention defined in claim 3 further comprising a metallic coated short circuit hole associated with each of said means for connecting an input signal.