Frequency agile-baseband sidelobe canceller

• US 3,881,177 A
• Filed: 03/12/1974
• Issued: 04/29/1975
• Est. Priority Date: 03/12/1974
• Status: Expired due to Term

• Current Assignee: Joseph F. Len, Peter M. Rankin
• Original Assignee: Joseph F. Len, Peter M. Rankin
• Inventors: Rankin, Peter M., Len, Joseph F.
• Primary Examiner(s): Tubbesing, T. H.
• Application Number:
  US05/450,543
• Time in Patent Office: 413 Days
• Field of Search: 343/18E,1CL,1LE 325/367,369,371
• US Class Current: 342/16
• 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 3/2629 Combination of a main antenna unit with an auxiliary antenna unit

Abstract

Undesirable sidelobe signals are cancelled from the returns of a main radar by the use of an omni antenna which will receive the undesired signal. The signals from the main antenna and the omni antenna are mixed together in a correlator which detects phase and amplitude difference therebetween. The correlator feeds its output to a modulator which amplitude modulates a signal from the omni antenna and feeds it to a signal subtraction circuit which is in series with the main antenna'"'"''"'"'s output. The correlator and the modulator are broken down into two parallel units which are 90* out of phase with each other.

Claims

1. A system comprising a main signal path containing therein a desired and an undesired signal;

a second signal path containing therein primarily the undesired signal;

cancellation means connected in the main signal path for substantially cancelling the undesired signal therein;

correlator means connected to said main signal path and said second signal path so as to measure the amplitude and phase difference of the undesired signal in each of these paths;

modulator means having inputs connected to outputs of said correlator means and said second signal path;

an output of said modulator means being connected to said cancellation means so as to subtract the output signal of the modulator from the signals contained in said main signal path;

said modulator means amplitude modulating the undesired signal in said second path such that the signal and its output is of the proper phase and amplitude to cancel in the cancellation means the undesired signal in said main signal path;

said main signal path is connected to an output terminal;

said cancellation means is connected between the main signal path and said output terminal;

said correlator means and said modulator means each contain two parallel paths;

one path containing a 90* phase shifting meas therein;

said correlator means contains first and second mixer means each having first and second inputs and an output;

said first and second mixer means being connected in different ones of the two parallel paths of the correlator means;

one input of the first mixer means is connected to the main signal path and the other input of the first mixer means is connected to said second signal path;

one input of the second mixer means is connected through the 90* phase shifter to the main signal path, and the other input is connected to said second signal path;

said modulator means containing first and second amplitude modulators in separate ones of the two parallel paths oF the modulator means;

said first and second modulators each having two inputs and an output;

the output of the first mixer means being connected to one input of the first modulator;

the other input of the first modulator being connected to said second signal path;

the output of the second mixer means being connected to one input of said second modulator;

the other input of the second modulator being connected to said second signal path;

the output of said second modulator being connected through the 90* phase shifter to the input of said cancellation means; and

the output of said first modulator being connected to the input of said cancellation means.

2. A system as set forth in claim 1 further comprising third and fourth mixer means each having first and second inputs and an output;

a local oscillator having an output connected to one input of each of said third and fourth mixer means;

the other input of said third mixer means being connected to said main signal path;

the other input of said fourth mixer means being connected to said second signal path;

first and second bandpass filters;

the output of said third mixer means being connected through said first bandpass filter to the input of said first mixer means; and

the output of said fourth mixer means being connected through said second bandpass filter to an input of said second mixer means.

3. A system as set forth in claim 2 further comprising a plurality of additional second signal paths each containing undesired signals which are to be found in said main signal path;

and a plurality of additional correlators and modulators associated with the additional second signal paths and connected in the manner of said original second signal path.

4. A system as set forth in claim 3 wherein said main signal path is supplied by a directional radar antenna;

and said plurality of second signal paths each being fed by one of a plurality of omni antenna.