Continuously transmitting and receiving radar

• US 4,968,967 A
• Filed: 10/06/1989
• Issued: 11/06/1990
• Est. Priority Date: 10/14/1988
• Status: Expired due to Fees

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Stove, Andrew G.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Hellner, Mark
• Application Number:
  US07/418,378
• Time in Patent Office: 396 Days
• Field of Search: 342/128, 342/165, 342/127, 342/198, 342/175
• US Class Current: 342/165
• CPC Class Codes: G01S 13/32 using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
• CPC Class Codes: G01S 7/038 Feedthrough nulling circuits
• CPC Class Codes: H04B 1/525 with means for reducing leakage of transmitter signal into the receiver

Abstract

A continuously transmitting and receiving radar comprises a transmitter (10), a receiver (16), an antenna (12) and a circulator (14) for effecting communication between the transmitter and the antenna and between the antenna and the receiver. A reflected power canceller is provided for suppressing the effects of leakage between the transmitter and receiver. The reflected power canceller comprises a directional coupler (20) for supplying a part of the transmitted signal to a modulator (22) which forms a cancelling signal by adjusting the phase and amplitude of the sampled signal. The cancelling signal is applied to another directional coupler (24) which subtracts the cancelling signal from the leakage and wanted signals. A narrowband control path is connected between the output of the receiver (16) and the modulator (22). The reduction in carrier leakage and AM noise sidebands is made more effective by providing a time delay device (21) in the signal path from the coupler (20) to the modulator (22). The time delay introduced by the device (21) is set so that the propagation times between the transmitter (10) and the directional coupler (24) via the circulator (14) and via the modulator (22) are the same. Optionally FM noise can be reduced by ensuring the propagation time of the local oscillator signal applied to a mixer in the receiver (16) is the same as that of the leakage path between the transmitter and receiver.

Claims

1. In a radar including a transmitter for producing a CW transmitter signal, an antenna coupled to the transmitter through a first coupling path for radiating the CW signal and receiving a return signal, a receiver coupled to the antenna through a second coupling path, and a feedthrough path through which a leakage portion of the CW signal is coupled to the second coupling path, said leakage portion including a carrier an AM sidebands, the improvement comprising means for reducing the magnitude of said leakage portion of the CW signal which is coupled to the receiver, said means comprising:

a. coupling means coupled to the first coupling path for producing a reduced-magnitude sample of the CW transmitter signal;

b. correction means having an input coupled to the first coupling path for adjusting the phase and amplitude of the sample to produce a correction signal including said carrier and AM sidebands;

c. subtraction means coupled to the correction means and to the second coupling path for subtracting the correction signal from the return signal to reduce the leakage portion of the CW signal coupled to the receiver;

d. time delay means for effecting correlation at the subtraction means of the AM sidebands in the correction signal and in the leakage portion of the CW signal, thereby minimizing and residual of the AM sidebands in the return signal coupled to the receiver; and

e. detection means coupled to the receiver for detecting any residual of the leakage portion and coupled to the correction means for producing a low frequency control signal to effect adjustment of the phase and amplitude of the correction signal to reduce said residual.

2. A radar as in claim 1 including means for reducing FM noise sidebands in the leakage portion of the CW signal coupled to the receiver, said means including a mixer having a first input coupled to the transmitter for receiving a sample of the CW transmitter signal, a second input coupled to the second coupling path, and time delay means for effecting correlation at the mixer inputs of the FM sidebands in said sample of the CW transmitter signal and in the leakage portion of the CW transmitter signal.

3. A radar as in claim 1 or 2 where the correction means comprises a vector modulator.

4. A method of reducing the effects of leakage in a radar including a transmitter for producing a CW transmitter signal, an antenna coupled to the transmitter through a first coupling path for radiating the CW signal and receiving a return signal, a receiver coupled to the antenna through a second coupling path, and a feedthrough path through which a leakage portion of the CW signal is coupled to the second coupling path, said leakage portion including a carrier and AM sidebands, the improvement comprising means for reducing the magnitude of said leakage portion of the CW signal which is coupled to the receiver, said method comprising:

a. producing a reduced-magnitude sample of the CW transmitter signal;

b. adjusting the phase and amplitude of the sample to produce a correction signal including said carrier and AM sidebands;

c. subtracting the correction signal from the return signal to reduce the leakage portion of the CW signal coupled to the receiver;

d. time delaying the arrival at the subtraction means of at least one of the correction signal and the leakage portion of the CW signal to effect correlation of the AM sidebands in the correction signal and in the leakage portion of the CW signal, thereby minimizing any residual of the AM sidebands in the return signal coupled to the receiver; and

e. detecting any residual of the leakage portion coupled to the receiver and producing a low frequency control signal to effect adjustment of the phase and amplitude of the correction signal to reduce said residual.