US3704463A

US3704463A - Direction finding antenna system

Info

Publication number: US3704463A
Application number: US42640A
Authority: US
Inventors: George H Barry
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1970-06-02
Filing date: 1970-06-02
Publication date: 1972-11-28
Anticipated expiration: 1989-11-28

Abstract

A direction finding antenna system having a large circle of active reflector antenna elements and a smaller concentric circle of focal point active antenna elements. The outer circle consists of several hundred antenna elements where each element comprises a horizontal one-half wave length horizontal dipole and a onefourth wave length vertical dipole. The horizontal dipole receives the incoming signal the output of which is amplified and applied to the input of the vertical dipole which then retransmits the signal. A group of reflector antenna elements forming a segment of the outer circle receive and retransmit the incoming signal to a focal point where the signal is received by a focal point antenna on the inner circle. The signal from the focal point antenna receiving the retransmitted signal thus represents the output of a directional antenna. A display of signal arrival direction is obtained from the output of the focal point antennas.

Description

United States atent Barry 51 Nov. 28, 1972 DIRECTION FINDING ANTENNA SYSTEM Inventor: George H. Barry, Saratoga, Calif.

Assignee: The United States of America as represented by the Secretary of the Navy Filed: June 2, 1970 Appl. No.: 42,640

References Cited UNITED STATES PATENTS 10/1968 Tillotson ..343/ 100 ST 2/1971 l-limmel et al....343/10O SA X 7/1962 Russell ..343/100 SA UX 4/1966 McFarland ..343/1OO SA X Primary Examiner-Benjamin A. Borchelt Assistant Exandner-Richard E. Berger Att0meyR. S. Sciascia and Charles D. B. Curry A direction finding antenna system having a large circle of active reflector antenna elements and a smaller concentric circle of focal point active antenna elements. The outer circle consists of several hundred antenna elements where each element comprises a horizontal one-half wave length horizontal dipole and a one-fourth wave length vertical dipole. The horizontal dipole receives the incoming signal the output of which is amplified and applied to the input of the vertical dipole which then retransmits the signal. A group of reflector antenna elements forming a segment of the outer circle receive and retransmit the incoming signal to a focal point where the signal is received by a focal point antenna on the inner circle. The signal from the focal point antenna receiving the retransmitted signal thus represents the output of a directional antenna. A display of signal arrival direction is obtained from the output of the focal point antennas.

7 Claims, 5 Drawing Figures PATENTEMuvza I972 SHEET 1 [1F 2 F, INVENTOR GEORGE H. BARR) f 6W7 ATTORNEY PAIENTED NDY28 I972 3. 704.463

sum 2 or 2 GROUND PLANE GROUND PLANE Fig. 4A F/ ...-4B Y DIRECTION FINDING ANTENNA SYSTEM The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the direction finding of any royalties thereon or therefor.

The present invention relates to an antenna system and more particularly to a large size direction finding reflector antenna system.

Currently used large size communications and direction-finding antennas typically have apertures on the order of 300 meters and beamwidths of from 2 to in the HF frequency range of from 30 down to 6 MHz. When HF signals are received on scanning arrays of this size it has been found that the pattern of the received signal energy traces out the response pattern of the antenna itself. Therefore, larger apertures could be quite useful to provide higher system gain and more precise signal discrimination.

One of the diff culties encountered with larger arrays is that their cost increases approximately as the square of their resolution. As the size of array increases, the cost of the elements themselves becomes insignificant as compared to, the cost of the cables required to assemble all of the signal samples and the cost of processing the signals to form beams. For either circular or linear arrays, the cable cost increases with the square of the aperture or the number of elements. The cost of signal processing also increases with the square of the aperture. As the number of elements increases more signals must be processed to form each beam, and more beams are required to cover a given sector.

The present invention overcomes the square law cost problem associated with existing large antenna systems by providinga very effective antenna system that has a cost factor that only increases linearly with the size.

Briefly, the present invention comprises a large circle of active reflector antenna elements and a smaller concentric circle of focal point antenna elements. A group of reflector antenna elements forming a segment of the outer circle receives and retransmits the incoming signal to a focal point where the signal is received on one of the focal point antennas on the inner circle. The signal from this focal point antenna establishes the direction from which the incoming signal is coming. The outer circle may consist of several hundred antenna elements, for example, where each element comprises a one-half wave length horizontal dipole and a vertical dipole having a wave length of one-fourth wave length. The horizontal dipole receives the incoming signal. The output of the horizontal dipole is amplified and applied to the input of the vertical dipole which then retransmits the signal. Vertical quarter wave length dipoles are used as focal point antennas to receive the retransmitted signals. Each of the focal point antennas are connected to signal processing equipment for rapid analysis.

Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a plan view of the antenna system of the present invention;

FIG. 2 is an enlarged segment of the antenna system of FIG. I;

FIG. 3 is a schematic drawing of one of the active reflection antenna elements of FIGS. 1 and 2;

FIG. 4A is a diagram illustrating the radiation pattern of a one-fourth wave length dipole; and

FIG. 4B is a diagram illustrating the radiation pattern of a one-half wave length dipole.

In FIG. I is illustrated a plan view of the antenna system of the present invention. This antenna system includes a roundhouse 11 which includes equipment for processing the received signals, a circular array of active reflector antenna elements 13, a circular array of low beam focal point antennas 15, and a circular array of high beam focal point antennas 17.

The incoming signal rays are shown by the parallel lines indicated by reference numeral 19. These parallel rays 19 have a wave front illustrated by parallel lines 21 which are perpendicular to parallel rays 19. The incoming wave front 21 which are perpendicular to parallel rays 19. The incoming wave front 21 of rays 19 are received and then reflected by reflector antenna elements 13, within segment B, to form reflected rays 23 having wave fronts 25 which are focused at point A of the low beam focal point antennas 15. The signal that is received by the focal point antennas are transmitted by coaxial cable 26, for example, back to the roundhouse 1 1, for signal processing.

In FIG. 2 is illustrated a segment of the circular array between

broken lines

27 and 29 of FIG. 1 and in FIG. 3 is illustrated one of the active reflector antenna elements 13 of FIGS. 1 and 2. Referring to FIGS. 2 and 3, each active reflector antenna element 13 includes a one-half wave length dipole 31, a one-fourth wave length dipole 33,

lead lines

35 and 37, amplifier 39 and amplifier output line 41. Dipole 31 is one-half wave length and feeds a

balanced transmission line

35 and 37 that feeds a balanced input of amplifier 39. Amplifier 39 feeds an unbalanced one-fourth wave length dipole 33 through coaxial line 41, for example. The radiation pattern of one-half wave length dipole 31 is as illustrated by dotted lines 42. The radiation pattern of onefourth wave length dipole 33 is illustrated by dotted lines 43. It should be noted that the bottom of antenna 33 is mounted on the ground that forms a ground plane. Dipole 31 may be mounted on a telephone pole, for example, or it may be mounted on suspended wires having electrical insulation between adjacent antennas. The surface of the ground plane is preferably salt water or wire mesh.

As shown and described, antenna 31 is a one-half wave length dipole; however, it is to be understood that if broad band reception is desired then another type antenna, such as a log periodic antenna, may be used in place of dipole 31. The received signal by dipole 31 is transmitted through

lead lines

35 and 37 which is preferably a balanced transmission line, to the input of amplifier 39. The output of amplifier 39 is transmitted through line 41, which may be of the coaxial type, to the lower end of antenna 33. The center conductor of line 41 is connected to the base of antenna 33 and the outer conductor is connected to ground. It should be particularly noted that antenna 33, which is a retransmitting antenna, is a one-fourth length antenna. This is because a one-fourth wave length antenna provides a radiation pattern that has a strong radiation component along the ground, as shown in FIG. 4A, so that it will transmit a strong signal to the focal point antennas l and 17. If antenna 33 were a one-half wave length antenna then there would be a very weak radiation com ponent along the ground, as shown in FIG. 48, so that only a very weak signal would be received by the focal point antennas. It should be noted that antenna 33 is preferably a one-fourth wave length antenna if the received signals are within a narrow band. However, if the received signals are broad band then very little energy would be transmitted to antennas or 17 when the received signal was twice the frequency at which antenna 33 is one-fourth wave length. Therefore, when broad band signals are received it is necessary that antenna 33 be less than one-half wave length.

In order to prevent the component array from having large 'side lobes and" therefore" poor component directivity (one dipole 31 by itself is not very directive) it is desirable to closely space (as indicated by distance d of FIG. 2) the adjacent antennas 31 so that the distance between centers of adjacent antennas is about one wave length.

The following table sets forth the system parameters of one example of an antenna system of the present invention. It will be obvious to one skilled in the art that these parameters may be changed so long as system compatibility is maintained.

TABLE I Diameter (D) 2000 meters Reflector antenna 31 spacing (d) 15 meters Number of elements 13 420 Number of active elements 13* 60 Reflector amplifier 39 gain l0 db at 3 MHz,

30 db at 30 MHz Receiving antenna 31 length 7% meters at MHz Receiving antenna 31 height (h) 15 meters Spacing of antennas 31 and 33 (l) 50 meters Reflector antenna 33 length =4 meters at 20 MHz Focal point antennas l5 and I7 ==4 meters at 20 MHz lengths Active elements are those elements 13 that are within the. sector that is collecting and focusing the received signal 'n focal point A. For example, those elements within the useful aperture 3" of FIG. 1. Because of spherical abberation the elements 13 outside of aperture B will not focus at point A.

"The size of these antennas is determined by the frequency of the received signals. At 20 MHz the antenna lengths are preferably as indicated. However, at a lower frequency; for example, l0 MHz, then the antenna lengths would double and the spacing d" would double.

It should be noted that the focal point A will shift radially depending upon the elevation from which the incoming signal is received. For example, if the incoming signal is arriving from 0 elevation or nearly horizontal to the surface of the earth, as is the case for most long distance communications, then the focal point will be on the outer circle of antennas 15. However, if the incoming signal is arriving from a elevation, for example, then the focal point will be on the inner circle of antennas 17. Additional circles of antennas similar to 15 and 17 may be necessary if the received signals arrive at very high angles. However, even at very high angles, antennas 17 will still be able to determine quite accurately the direction from which the incoming signal is arriving. This is because the center antenna will receive the strongest signal, indicating the direction from which the signal is coming, and the signals on either sidewill have lesser signals and by simple plotting of the received strengths it is possible to accurately determine the antenna receiving maximum signal.

What is claimed is:

1. An antenna system comprising:

a. an outer circle of a plurality of first antenna elements;

b. each of saidv first antenna elements in said outer circle of first antenna elements includes an amplifier for amplifying an incoming signal to said antenna system;

c. an inner circle of a plurality of second antenna elements;

d. said outer circle of antenna elements receiving an incoming signal arriving from a predetermined direction and retransmitting the received signal to a focal point on said inner circle of said second antenna elements; and

e. whereby said focal point identifies said predetermined direction.

2. The system of claim 1 wherein each of said first antenna elements comprises:

a. a first dipole mounted parallel to ground for receiving said incoming signals;

b. a second dipole mounted vertical to ground;

c. means for transmitting the incoming signal received by said first dipoleto said second dipole; and

d. said second dipole retransmits the signal to said focal point.

3. The system of claim 2 wherein:

a. saidfirst dipole has a length of about one-half of the wave length of said incoming signal.

4. The system of claim 3 wherein:

a. said second dipole has a length of less than about one-half of the wave length of said incoming signal.

5. The system of claim 4 wherein:

a. the distance between center positions of said first dipoles forming said outer circle is about the wave length of said incoming signal.

6. The systernof claim 5 wherein:

a. I one end of said second dipole is connected to ground.

7. The system of claim 1 wherein each of said first antenna elements comprises:

a. a receiving element for receiving said incoming signals and having an input and an output;

b. said amplifier including an amplifier element having an input and an output;

0. a retransmitting element having an input and an output; and t 'd. the input of said amplifying element being operatively connected to the output of said receiving element and the input of said retransmitting element being connected to the output of said amplifier element.

Claims

1. An antenna system comprising: a. an outer circle of a plurality of first antenna elements; b. each of said first antenna elements in said outer circle of first antenna elements includes an amplifier for amplifying an incoming signal to said antenna system; c. an inner circle of a plurality of second antenna elements; d. said outer circle of antenna elements receiving an incoming signal arriving from a predetermined direction and retransmitting the received signal to a focal point on said inner circle of said second antenna elements; and e. whereby said focal point identifies said predetermined direction.

2. The system of claim 1 wherein each of said first antenna elements comprises: a. a first dipole mounted parallel to ground for receiving said incoming signals; b. a second dipole mounted vertical to ground; c. means for transmitting the incoming signal received by said first dipole to said second dipole; and d. said second dipole retransmits the signal to said focal point.

3. The system of claim 2 wherein: a. said first dipole has a length of about one-half of the wave length of said incoming signal.

4. The system of claim 3 wherein: a. said second dipole has a length of less than about one-half of the wave length of said incoming signal.

5. The system of claim 4 wherein: a. the distance between center positions of said first dipoles forming said outer circle is about the wave length of said incoming signal.

6. The system of claim 5 wherein: a. one end of said second dipole is connected to ground.

7. The system of claim 1 wherein each of said first antenna elements comprises: a. a receiving element for receiving said incoming signals and having an input and an output; b. said amplifier including an amplifier element having an input and an output; c. a retransmitting element having an input and an output; and d. the input of said amplifying element being operatively connected to the output of said receiving element and the input of said retransmitting element being connected to the output of said amplifier element.