Broadband direction finding system

• US 5,274,389 A
• Filed: 12/14/1992
• Issued: 12/28/1993
• Est. Priority Date: 06/21/1990
• Status: Expired due to Term

• Current Assignee: OL Security LLC (Intellectual Ventures LLC)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Archer, Donald H., McInturff, Kim, Mintzer, Alfred I., Thies, Wilbur H.
• Primary Examiner(s): Mintel, William
• Assistant Examiner(s): BROWN, PETER T
• Application Number:
  US07/990,817
• Time in Patent Office: 379 Days
• Field of Search: 342/427, 342/432, 342/437, 342/429, 342/417, 343/754, 343/853, 343/703, 343/844, 343/824, 343/792.5
• US Class Current: 343/754
• CPC Class Codes: H01Q 25/008 lens fed multibeam arrays
• CPC Class Codes: H01Q 3/242 Circumferential scanning

Abstract

An amplitude monopulse direction finding system is disclosed. The system is built around a circular array with a circular lens in which the antenna elements and array ports are larger than in conventional systems. The oversized antenna elements and array ports provide a wide range of operating frequencies for the direction finding system. Additionally, the direction finding system contains an omni-directional probe at the center of the lens to detect the presence of signals. In an alternative embodiment, each array port is split into two halves which can be combined in different ways to produce different beam patterns, allowing the beam pattern providing the best signal to noise ratio to be selected. Also, built-in-test circuitry is described.

Claims

1. A method of operating a direction finding system with a circular antenna array and a circular lens, to determine the direction of a signal received by the system, comprising the steps of:

a) comparing the strength of a first signal at the center of the lens and the strength of a second signal formed by the lens; and

b) when the strength of the second signal formed by the lens is of the same order of magnitude as the strength of the first signal at the center of the lens, using the second signal formed by the lens for computing the direction of the received signal.

3. The radio frequency system of claim 1 wherein the array ports and the antenna elements have different dielectric media and wherein the center-to-center spacing between the array ports measured along an arc of the circularly disposed array ports is 6.65 λ

_H.

7. The radio frequency system of claim 3 additionally comprising an omnidirectional probe in the center of the circular lens.

2. A radio frequency system adapted for operation with signals having frequencies within a predetermined bandwidth, such predetermined bandwidth extending from a lowest frequency f_L to a highest frequency f_h comprising:

a circular array of antenna elements, the center-to-center spacing between the antenna elements measured along the outer circumference of the circular array being 3.5 λ

_H, where λ

_H =c/f_H and where c is equal to the speed of light in free space; and

additionally comprising;

a circular lens means, having a plurality of circularly disposed array ports disposed along an outer periphery of the lens means, for coupling energy fed to one of such array ports, through the lens means, to other ones of the array ports, each one of the plurality of array ports being coupled to a corresponding one of the antenna elements.

4. The radio frequency system of claim 2 additionally comprising:

a circular lens having a plurality of array ports, each one of the antenna elements being coupled to a different pair of two adjacent ones of the plurality of array ports.

5. The radio frequency system of claim 4 wherein the array ports and the antenna elements have different dielectric media and wherein the spacing between the array ports is 3.3 λ

_H.

6. The radio frequency system of claim 2 additionally comprising an omnidirectional probe in the center of the circular lens.

8. A direction finding system adapted for operation with signals having frequencies within a predetermined bandwidth, such predetermined bandwidth extending from a lowest frequency F_L to a highest frequency f_H comprising:

a circular array of antenna elements, the spacing between antenna elements exceeding λ

_H where λ

_H =c/f_H, and where c is equal to the speed of light in free space; and

additionally comprising;

a circular lens means, having a plurality of array ports disposed along an outer periphery of the lens means, for coupling energy fed to one of such array ports, through the lens means, to other ones of the array ports, wherein each one of the antenna elements is electrically connected to a corresponding one of said plurality of array ports.

9. The direction finding system of claim 8 wherein each one of the plurality of antenna elements is connected to a plurality of the plurality of array ports.

10. The direction finding system of claim 9 additionally comprising:

means, switchably coupled to two adjacent ones of the connected array ports, for receiving one radio frequency signal.

11. The direction finding system of claim 10 wherein the receiving means comprises means for computing an amplitude monopulse ratio of signals received at any two adjacent ones of the connected array ports.

12. The direction finding system of claim 9 additionally comprising:

a) an omnidirectional antenna element in the center of the circular lens;

b) means for processing signals; and

c) means for switchably coupling a signal received at one of the plurality of array ports to the processing means when the strength of a signal received at the omnidirectional antenna element is of the same magnitude as the signal received at said one of the array ports.

13. An antenna system adapted for operating on radio frequency signals having frequencies within a predetermined bandwidth, such predetermined bandwidth extending from a lowest frequency f_L to a highest frequency f_H comprising:

a) a plurality of antenna elements arranged in a circular array, such antenna elements having a center-to-center spacing greater than λ

_H, where λ

_H =c/f_H and where c is the speed of light in free space, each one of the antenna elements having an antenna element radiation pattern which varies with the frequency of the radio frequency signals;

b) a radio frequency lens means having a plurality of array ports disposed about an outer periphery of such lens for coupling an RF signal at one of the array ports to selected other ones of the array ports to produce an array port radiation pattern, such array port radiation pattern being coupled through the lens to an opposing selected portion of other ones of the array ports, the portion of such other ones of the array port having energy coupled thereto being a function of the frequency of the RF signal such that the width of the array port radiation pattern varies inversely with increasing frequency, and the width of the antenna element radiation pattern varies inversely with increasing frequency, to produce an antenna pattern for the antenna system which is constant over the predetermined bandwidth.

14. The antenna system of claim 13 wherein the antenna elements form a circular array.

15. The antenna system of claim 14 wherein each antenna element has a width in excess of one-half of a wavelength of the radio frequency signal.

16. The antenna system of claim 14 wherein f_H is in the range of 9f_L.

17. The antenna system of claim 14 wherein the array ports are disposed in a circle.

18. A direction finding system comprising:

a) a circular lens having a plurality of array ports;

b) means, having two inputs, for computing the amplitude monopulse ratio of the signals at the inputs;

c) first switching means for coupling a selected one of the array ports to a first one of the inputs of the computing means;

d) second switching means for coupling a selected different one of the array ports to a second one of the inputs of the computing means;

e) means for coupling a test signal to the first switching means and to the first one of the inputs of the computing means and for controlling the first switching means to couple the test signal to the first selected one of the array ports and for controlling the second switching means to connect the selected different one of the array ports to the second input of the computing means.

19. The direction finding system of claim 18 wherein the means for coupling comprises a signal coupler in the signal path between the first switching means and the first one of the inputs of the computing means.

20. The direction finding system of claim 18 wherein the computing means also comprises processing means for determining if the amplitude monopulse ratio of the test signals applied to the first and second inputs indicates an error condition.

21. The direction finding system of claim 18 wherein the means for coupling a test signal comprises built in test circuitry including an oscillator.