Focusing control of synthetic aperture processing for sidelooking radar

Claim 2

In a side-looking synthetic antenna type coherent radar adapted for airborne use, and having a stable intermediate frequency reference source and a clutter-reference intermediate frequency receiver stage, doppler data focusing means comprising a phase sensitive detector having a first input coupled to an output of said intermediate frequency receiver stage and further having a second reference input for providing a video output; and compensatory phase-shift means intercoupling an output of said reference source and said reference input of said phase sensitive detector, and being responsive to the platform velocity and system pulse repetition frequency of said radar system for modulating said reference input to said phase sensitive detector to provide doppler focusing of said video output of said detector for a preselected region of radar ranges.

Claim 3

The device of claim 1 in which said compensatory phase shift means includes function generator means for controlling said modulation in accordance with the function, (Vt)2/RM , where: V platform velocity t cyclical doppler processing time RM periodic radar range time.

Claim 4

In a side-looking synthetic antenna type coherent radar adapted for airborne use, and having a stable intermediate frequency reference source, a clutter-referenced intermediate frequency receiver stage, doppler data focusing means comprising a phase sensitive detector having a first input coupled to an output of said intermediate frequency receiver stage and further having a second reference input; a voltage-controlled phase shifter intercoupling an output of said reference source and said reference input of said phase sensitive detector, and further having a control input; and control means responsive to the platform velocity of said radar for generating a doppler focusing control output signal as a function of both radar system range time and the system doppler processing interval, said control input of said voltage controlled phase shifter being responsive to said doppler focusing control output signal.

Claim 5

In a side-looking synthetic antenna type coherent radar adapted for airborne use, and having a stable intermediate frequency reference source, a clutter-referenced intermediate frequency receiver stage, doppler data focusing means comprising a phase sensitive detector having a first input coupled to an output of said intermediate frequency receiver stage and further having a second reference input; a voltage-controlled phase shifter intercoupling an output of said reference source and said reference input of said phase sensitive detector, and further having a control input; and control means responsive to the platform velocity of said radar for generating a doppler focusing control output signal as a function of both radar system range time and the system doppler processing interval, said control input of said voltage controlled phase shifter being responsive to said doppler focusing control output signal.

Claim 6

The device of claim 3 in which said control means includes function generator means responsive to platform velocity V, radar range time RM and doppler processing interval for generating a control signal indicative of the function, 2 pi V2t2/ lambda RM, where lambda is the wavelength of said radar.

Claim 7

In a side-looking synthetic antenna type coherent radar adapted for airborne use and having a stable intermediate frequency reference source and a clutter-referenced intermediate frequency receiver stage, the improvement of data focusing means comprising a phase sensitive detector having a first input coupled to an output of said intermediate frequency receiver stage and further having a second reference input; a voltage-controlled phase shifter intercoupling an output of said reference source and said reference input of said phase sensitive detector, and further having a control input; control means for generating a doppler focusing control output signal indicative of the relationship: Delta phi (t) 2 pi / lambda (Vt)2/RM where: lambda radar transmitter wavelength V radar platform velocity RM radar range time t cyclical time over the doppler processing interval said control input of said voltage controlled phase shifter being responsive to said doppler focusing signal.

Claim 8

In a side-looking synthetic antenna type coherent radar adapted for airborne use and having a stable intermediate frequency reference source and a clutter-referenced intermediate frequency receiver stage, the improvement of data focusing means comprising a phase sensitive detector having a first input coupled to an output of said intermediate frequency receiver stage and further having a second reference input; a voltage-controlled phase shifter intercoupling an output of said reference source and said reference input of said phase sensitive detector, and further having a control input; control means for generating a doppler focusing control output signal indicative of the relationship: Delta phi (t) 2 pi / lambda (Vt)2/RM where: lambda radar transmitter wavelength V radar platform velocity RM radar range time t cyclical time over the doppler processing interval said control input of said voltage controlled phase shifter being responsive to said doppler focusing signal.

Claim 9

The Device of claim 5 in which said control means comprises first function generator means responsive to the platform velocity V of said radar and to cyclical doppler processing time t for generating a signal indicative of the square of the product of V and t, second function generator means responsive to an output of said first function generator means and a system trigger of said radar for modulating said output of said first function generator means as an inverse function of radar range time.

Claim 10

In a side-looking synthetic antenna type coherent radar adapted for airborne use, and having a stable intermediate frequency reference source, a clutter-referenced intermediate frequency receiver stage, the improvement data focusing means comprising a phase sensitive detector having a first input coupled to an output of said intermediate frequency receiver stage and further having a second reference input; modulation means intercoupling an output of said reference source and said reference input of said phase sensitive detector, and further having a modulation control input; modulation control means responsive to the platform velocity of said radar for generating a modulating control signal as a function of both radar system range time and the system doppler processing interval, said modulation control input of said modulation means being responsive to said modulating signal.

Claim 11

In a side-looking synthetic antenna type coherent radar adapted for airborne use, and having a stable intermediate frequency reference source, a clutter-referenced intermediate frequency receiver stage, the improvement data focusing means comprising a phase sensitive detector having a first input coupled to an output of said intermediate frequency receiver stage and further having a second reference input; modulation means intercoupling an output of said reference source and said reference input of said phase sensitive detector, and further having a modulation control input; modulation control means responsive to the platform velocity of said radar for generating a modulating control signal as a function of both radar system range time and the system doppler processing interval, said modulation control input of said modulation means being responsive to said modulating signal.

Claim 12

The device of claim 7 in which said modulation means comprises a single sideband modulator and in which said modulating signal means comprises a voltage controlled oscillator and means for varying the frequency of said oscillator by an mount Delta f in accordance with the relationship: Delta f V2t/ lambda RM where: V radar platform velocity t periodic doppler processing time RM radar range time lambda radar system transmitter wavelength.

Claim 13

The device of claim 7 in which said means for generating comprises first function generator means for generating an output signal indicative of the function V2; inverse function generator means responsive to a system trigger of said radar for modulating said output signal of said first function generator as an inverse function 1/RM of periodic range time; third function generator means for modulating the output of said inverse function generator means as a direct function of periodic time t; and voltage controlled oscillator means responsive to said doubly modulated output of said third function generator for providing a modulating control signal input to said modulating means.

Claim 14

The device of claim 7 in which said means for generating comprises first function generator means responsive to the platform velocity of said radar for generating an output signal indicative of the function V2 cos2 phi ; second function generator means responsive to a system trigger of said radar for modulating said output signal of said first function generator as an inverse function of periodic range time and as a direct function of a periodic doppler processing interval; and voltage controlled oscillator means responsive to said modulated output of said second function generator for modulation control of said modulating means.

Claim 15

A coherent radar system having a simplified in-focus synthetic antenna mode, comprising a side-looking antenna; a pulsed coherent radio frequency transmitter output coupled to said antenna; a receiver having an input coupled to said antenna and further having an intermediate frequency stage including an auxiliary local oscillator injection input; doppler frequency tracking means responsive to an output of said intermediate frequency stage for providing an auxiliary local oscillator signal at said injection input of said intermediate frequency stage, whereby said output of said intermediate frequency stagE is clutter referenced; phase sensitive detector means having a first input coupled to said output of said intermediate frequency stage and further having a reference second input responsively coupled to a coherent source of a reference intermediate frequency signal for providing a video output; and compensatory phase-shift means responsive to the platform velocity and system pulse repetition frequency of said radar system for modulating said reference input to said phase sensitive detector to provide doppler focusing of said video output of said detector for a preselected region of radar ranges.

Claim 16

A coherent radar system having a simplified in-focus synthetic antenna mode, comprising a side-looking antenna; a pulsed coherent radio frequency transmitter output coupled to said antenna; a receiver having an input coupled to said antenna and further having an intermediate frequency stage including an auxiliary local oscillator injection input; doppler frequency tracking means responsive to an output of said intermediate frequency stage for providing an auxiliary local oscillator signal at said injection input of said intermediate frequency stage, whereby said output of said intermediate frequency stagE is clutter referenced; phase sensitive detector means having a first input coupled to said output of said intermediate frequency stage and further having a reference second input responsively coupled to a coherent source of a reference intermediate frequency signal for providing a video output; and compensatory phase-shift means responsive to the platform velocity and system pulse repetition frequency of said radar system for modulating said reference input to said phase sensitive detector to provide doppler focusing of said video output of said detector for a preselected region of radar ranges.

Claim 17

The device of claim 11 in which said compensatory phase shift means comprises first function generator means for generating an output signal indicative of the function V2cos2 phi ; inverse function generator means responsive to a system trigger of said radar for modulating said output signal of said first function generator as an inverse function of periodic range time; third function generator means for modulating the output of said inverse function generator means as a direct function of a periodic doppler processing interval; voltage controlled oscillator means responsive to said doubly modulated output for generating a modulation control signal output; and single sideband modulation means interposed between said output of said coherent source and said second input of said phase detector and having a modulation input responsive to the control signal output of said oscillator means.

Claim 18

The device of claim 7 in which said compensatory phase shift means comprises first function generator means responsive to the platform velocity of said radar for generating an output signal indicative of the function V2; second function generator means responsive to a system trigger of said radar for modulating said output signal of said first function generator as an inverse function of periodic range time and as a direct function of a periodic doppler processing interval; voltage controlled oscillator means responsive to said modulated output of said second function generator for generating a control signal; and single sideband modulation means interposed betwen said output of said coherence source and said second input of said phase detector and having a control input responsive to the control signal output of said oscillator means.