US3121230A

US3121230A - Portable ground plane mat with cavity backed antennas placed thereon

Info

Publication number: US3121230A
Application number: US92720A
Authority: US
Inventors: Brueckmann Helmut
Original assignee: Individual
Current assignee: Individual
Priority date: 1961-03-01
Filing date: 1961-03-01
Publication date: 1964-02-11
Anticipated expiration: 1981-02-11

Description

was

Feb. 11, 1964 H. BRUECKMANN PORTABLE GROUND PLANE MAT WITH CAVITY BACKED ANTENNAS PLACED THEREON Filed March 1, 1961 [II/Ill I/I/I/I/I/I/I/I/I I I JNVENTOR,

HELMUT BRUECKMANN ATTORNEY.

United States Patent 3,121,230 PORTABLE GROUND PLANE MAT WITH CAVITY BACKED ANTENNAS PLACED TIIEREON Helmut Brueckmann, Little Silver, NJ., assignor to the United States of America as represented by the Secretary of the Army Filed Mar. 1, 1961, Ser. No. 92,720 7 Claims. (Cl. 343-770) (Granted under Title 35, U.S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

This invention relates to antennas and, more particularly, to a portable, low-profile antenna which is relatively immune to ground effects.

The radiation characteristics of an antenna are affected by the electrical properties of the ground beneath it. These ground effects can be taken into account as long as the electrical properties of the ground are known thereby making possible adjustments of the antenna characteristics to achieve the desired radiation pattern for an antenna at a fixcd location. However, in the case of portable antennas prior to this invention ground effects constituted a serious problem for which there was no simple solution, especially for low level or low-profile antennas.

In the case of radio beacon antennas for air navigation and for communication and telemetering from ground to air in systems such as missile guidance and satellite communication, the variations of the radiation characteristics due to varying ground properties cannot be tolerated. 1n the past, elevated dipole antennas and the like were used in such applications, but in order to overcome ground effects, such antennas must be mounted a considerable distance above ground with respect to the wavelength at the operating frequency. This results in the necessity of constructing a supporting tower or framework. The obvious disadvantages of such elevated antenna structures are that'they create a definite hazard to aircraft when used near aircraft runways as beacon antennas, and they have high wind drag.

According to this invention a new, portable, low-profile antenna system has been developed which minimizes ground effects and eliminates the extra supporting tower,

or framework previously necessary to elevate the antenna in order to overcome ground effects.

In a preferred embodiment of this invention a metallic sheet, such as aluminum foil or a wire mesh, is imbedded in or coated with a rubberlike plastic such 'as Mylar and is laid directly on the ground. Cavity-backed slot antenna elements are placed on the plastic covered sheet in any desired arrangement, depending on the particular application, frequency of operation, desired pattern, desired polarization, etc. The sheet extends beyond the antenna elements and minimizes ground effects.

Accordingly, it is an object of this invention to provide an antenna system which is relatively immune to ground effects.

Another object of this invention is to provide a portable, low-profile antenna system.

A more specific object of this invention is to provide an antenna system which minimizes ground effects without the use of elevated structures.

A further object of this invention is to provide a lowprofile antenna system which has low wind drag.

Other objects and features of this invention will become apparent to those skilled in the art upon consideration of the following detailed description taken in conjunction with the drawing, the single figure of which shows a preferred embodiment of the invention.

Referring now to the drawing in detail, there is shown in a partially cut away view a ground sheet 10 comprising a thin metallic layer '11 covered on each surface by layers of suitable dielectric material 12. Sheet 10 is placed or laid directly on the ground or over water, and a number of antenna elements 13 are mounted directly on the upper surface of sheet 10 in any desired arrangement depending upon the radiation pattern desired for particular applications. For purposes of illustration, antenna elements 13 have been arranged to form a broadside array having Patented Feb. 11, 1964 three parallel rows of elements fed by .a coaxial input line lfi yvhich, in turn, is connected to a suitable transmitter and/or receiver, not shown. With the feed system shown, the inputs to an antenna elements 13 are spaced V2) apart, where A is the wavelength at the operating frequency. This particular arrangement is a narrow-band, frequencysensitive antenna, and it was chosen for this illustration because of its simplicity. For broad-band applications, a feed system having equal lengths of feed line to all elements 13 would be used.

Each antenna element 13 is constructed having a sheet of dielectric material 15, such as a flexible ferrite or styrofoam, covered on all its surfaces but one with a metal conductive member 14. The open or uncovered surface of dielectric sheet 15 forms a slot in member 14. Energy is then fed to the mid-point of this slot from line 16. Each antenna element 13 functions in the manner of a slot antenna backed by a cavity which, in this case, consists of a stripline. The particular antenna elements shown were chosen because they have a low profile, for example, at me. they extend only Auk or less above sheet 10, where )t is the operating wavelength of the syswithout the necessity of then determining and compensating for or eliminating the ground effects for each different installation.

A high degree of portability is obtained, especially when it is considered that sheet 10 is very thin and flexible and can be rolled up like a blanket during transportation. For portable systems, the location of the desired arrangementor arrangements of the antenna elements 13 can be marked out on the upper layer 12 of sheet 10, facilitating proper location of elements 13 when the system is set up in a new location. Antenna elements '13 may be fastened to sheet 10 by any suitable means or they may be placed on sheet 10 without any fastening means whatsoever depending on the situation in which the antenna system is to be used. Direct connection of elements 13 to metal layer 11 is not necessary since the capacity between the lower surface of elements 13 and layer 11 is large, amounting to a short.

It is to be understood that the invention is not limited to the particular type of antenna elements shown but that any cavity-backed slot antenna elements could be used. Also, the layer of metal foil 11 in sheet 10 could be replaced by a layer of wire mesh if so desired. Wire mesh may be more desirable for high frequency installations covering a large area; and in such installations, the mesh could be placed on top of wooden planks laid on the ground in place of using Mylar which would be more expensive. The specific embodiment shown is merely illustrative of the principles of the invention, and various changes and modifications may be made without departing from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. An antenna comprising a fiat, flexible sheet having an inner layer and two outer layers, said inner layer being of highly conductive material and said outer layers being of solid dielectric material, at least one cavity-backed slot antenna element mounted directly on said dielectric material and spaced from said highly conductive material, and a transmission line connected to said antenna element.

2. An antenna according to claim 1 where said inner layer is a continuous sheet of metal foil.

3. An antenna according to claim 1 where said inner layer is a wire mesh.

4. An antenna comprising a substantially fiat, flexible ground sheet having an inner layer of highly conductive material covered on each surface by a layer of solid di electric material, a plurality of spaced antenna elements mounted directly on the surface of said sheet in an array, said antenna elements being unattached to said ground sheet and spaced from said highly conductive material, said ground sheet extending beyond the area covered by said antenna elements at least AA or more, where A is the wavelength at the operating frequency of said antenna, whereby said ground sheet acts to minimize ground effects, and a transmission line connected to said antenna elements.

5. An antenna according to claim 4 where said inner layer is a continuous sheet of metal foil.

6. An antenna including a flat flexible shcct having at least two layers, one of said layers being a highly conductive material and the other said layers being a dielectric material, at least one cavity-backed slot antenna element resting on said sheetand unattached thereto, and a transmission line connected to said antenna element.

7. An antenna comprising in combination; a layer 0t highly conductive material covered on each surface by a layer of solid dielectric material, and a plurality of cavitybacked slot-antenna elements mounted on said dielectric material and spaced from said conductive material, said slot-antenna elements being unattached to said conductive layer.

References Cited in the file of this patent UNITED STATES PATENTS 1,685,875 Fishwick Oct. 2, 1928 2,364,084 Martin Dec. 5, 1944 2,433,369 Kandoian Dec. 30, 1947 2,557,951 De Rosa et a1 June 26, 1951 2,684,444 Fales July 20, 1954 2,840,819 McClellan June 24, 1958 2,929,065 Kreinheder Mar. 15, 1960 2,993,205 Cooper July 18, 1961 2,996,713 Boyer Aug. 15, 1961 3,096,520 Ehrenspeck July 2, 1963

Claims

1. AN ANTENNA COMPRISING A FLAT, FLEXIBLE SHEET HAVING AN INNER LAYER AND TWO OUTER LAYERS, SAID INNER LAYER BEING OF HIGHLY CONDUCTIVE MATERIAL AND SAID OUTER LAYERS BEING OF SOLID DIELECTRIC MATERIAL, AT LEAST ONE CAVITY-BACKED SLOT ANTENNA ELEMENT MOUNTED DIRECTLY ON SAID DIELECTRIC MATERIAL AND SPACED FROM SAID HIGHLY CONDUCTIVE MATERIAL, AND A TRANSMISSION LINE CONNECTED TO SAID ANTENNA ELEMENT.