Power rejection apparatus using a null-constrained subarray for MTI radar applications

• US 4,070,675 A
• Filed: 10/21/1976
• Issued: 01/24/1978
• Est. Priority Date: 10/21/1976
• Status: Expired due to Term

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Daniel, Sam M., Carlson, Eric Jerome
• Primary Examiner(s): Wilbur, Maynard R.
• Assistant Examiner(s): Berger, Richard E.
• Application Number:
  US05/734,699
• Time in Patent Office: 460 Days
• Field of Search: 343/100 LE, 343/7.7
• US Class Current: 342/380
• CPC Class Codes: G01S 7/2813 Means providing a modification of the radiation pattern for cancelling noise, clutter or interfering signals, e.g. side lobe suppression, side lobe blanking, null-steering arrays specially adapted to secondary radar systems G01S13/762; aerials or aerials systems H01Q21/29, H01Q25/00
• CPC Class Codes: H01Q 1/00 Details of, or arrangements associated with, antennas arrangements for varying orientation of directional pattern H01Q3/00
• CPC Class Codes: H01Q 21/06 Arrays of individually energised antenna units similarly polarised and spaced apart
• CPC Class Codes: H01Q 3/2635 the auxiliary unit being composed of a plurality of antennas

Abstract

The present invention involves the use of an adaptive power injection apparatus with an existing antenna having a radiation pattern characterized by a relatively narrow main beam and a plurality of low level sidelobes for the purpose of enhancing the performance of the main antenna in a jamming evironment. The said apparatus consists of an adaptive subarray constrained to maintain a null in the direction of the main beam of the existing antenna. More specifically, the said adaptive array is composed of several individual antennae having relatively wide-beam patterns and combined with the existing antenna through individual IF stages all identical to the IF stage of the existing antenna, individual phase shifters which provide phases necessary for maximum reception from the direction of the main beam of the existing antenna and individual adjustable weights. The weights, which may consist of voltage controlled amplifiers or equivalent devices are adjusted by means of individual signals derived from correlating each corresponding auxilliary antenna signal with the combined signal at the output of the summing network and subsequently subtracting each such signal from the overall average. Setting the weights originally to have a zero average value creates a null in the direction of the main beam. Consequently, subsequent weight adjustments by means of individual adjusting signals whose combined average is zero will maintain the null in the said direction. In an MTI application, the apparatus described would leave the main beam practically intact while serving, at the same time, to mimimize interferring sidelobe power. Thus avoiding undesirable amplitude modulation of the main beam signals that would otherwise arise without the presence of the constrained null.

Claims

1. In a communications system, such as radar and the like, including a main antenna having a radiation pattern characterized by a relatively narrow main lobe and a plurality of relatively low sidelobes, adaptive sidelobe power rejection apparatus using a null-constrained subarray comprising:

a. A plurality of secondary antennas forming a subarray;

b. Phase shifting means coupled to said secondary antennas for shifting the phase of output signals to any predetermined phase;

c. Adjustable weighting means coupled to said phase shifting means and providing outputs weighted in accordance with the adjustments of said weighting means;

d. Combining means connected to the main antenna for receiving output signals therefrom and connected to said weighting means for receiving the outputs therefrom, said combining means having an output; and

e. Controller means coupled to said secondary antennas, the output of said combining means and said adjustable weighting means for adjusting said weighting means so that the radiation pattern of said secondary antennas minimizes the sidelobe power in the radiation pattern of said main antenna and has substantially no effect on the main lobe of the main antenna.

2. Adaptive sidelobe power rejection apparatus as claimed in claim 1 wherein the controller means includes correlation means for correlating signals at the output of the combining means and signals at each of the plurality of secondary antenna for providing a plurality of correlated signals.

3. Adaptive sidelobe power rejection apparatus as claimed in claim 2 wherein the controller means includes averaging means coupled to the correlation means for providing an average signal indicative of the average of all of the correlated signals and for subtracting each correlated signal from this average.

4. Adaptive sidelobe power rejection apparatus as claimed in claim 3 wherein the controller means includes means of connecting the correlated signals minus the average signal to the adjustable weighting means for controlling the weighting of the signals passing therethrough.

5. Adaptive sidelobe power rejection apparatus as claimed in claim 1 wherein the phase shifting means is adjusted so that a null is formed in the pattern of the sub-array in the direction of the main lobe of the main antenna when the sum of all the weights in the adjustable weighting means is equal to zero.

6. Adaptive sidelobe power rejection apparatus as claimed in claim 1 wherein integrating means are coupled into the loop including the adjustable weighting means, the combining means and the controller means for smoothing the signals in the loop and providing some memory.

7. Adaptive sidelobe power rejection apparatus as claimed in claim 1 wherein the communications system is a moving target indicator (MTI) radar.