Means for suppressing ground clutter in airborne radar

Claim 3

A radar system carried aloft by aircraft for detecting long range and short range elevated targets while suppressing ground clutter, the system comprising: means for transmitting ranging pulses for illuminating said targets which respond by reflecting echo signals; receive antenna means responsive to said echo signals for providing a receive antenna beam in a first beam position; first circuit means for steering said receive antenna beam from said first beam position to a second beam position in response to a beam steering program, said first circuit means coupled to said antenna means and including first and second channels, said first channel including a first duplexer and said second channel including a second duplexer, a controllable attenuator, and a controllable phasor connected in circuit; a function generator responding to an altitude reference for generating output signals to said controllable attenuator and said controllable phasor which generate said beam steering program; second circuit means including series connected mixer, amplifier and detector for deriving substantially clutter free information regarding said elevated targets from said receive antenna means; and display means coupled to said second circuit means for displaying said signal derived from said antenna means.

Claim 4

A radar system carried aloft by aircraft for detecting long range and short range elevated targets while suppressing ground clutter, the system comprising: means for transmitting ranging pulses for illuminating said targets which respond by reflecting echo signals; receive antenna means responsive to said echo signals for providing a receive antenna beam in a first beam position; first circuit means for steering said receive antenna beam from said first beam position to a second beam position in response to a beam steering program, said first circuit means coupled to said antenna means and including first and second channels, said first channel including a first duplexer and said second channel including a second duplexer, a controllable attenuator, and a controllable phasor connected in circuit; a function generator responding to an altitude reference for generating output signals to said controllable attenuator and said controllable phasor which generate said beam steering program; second circuit means including series connected mixer, amplifier and detector for deriving substantially clutter free information regarding said elevated targets from said receive antenna means; and display means coupled to said second circuit means for displaying said signal derived from said antenna means.

Claim 5

receive antenna means responsive to said echo signals including at least one radiator for providing a receive antenna beam in a first beam position;

Claim 6

receive antenna means responsive to said echo signals including at least one radiator for providing a receive antenna beam in a first beam position;

Claim 7

first circuit means for steering said receive antenna beam from said first beam position to a second beam position in accordance with a beam steering program, coupled to said antenna means and including first and second channels, said first channel including a first duplexer and said second channel including a series connected second duplexer, a controllable attenuator, and a controllable phasor.

Claim 8

first circuit means for steering said receive antenna beam from said first beam position to a second beam position in accordance with a beam steering program, coupled to said antenna means and including first and second channels, said first channel including a first duplexer and said second channel including a series connected second duplexer, a controllable attenuator, and a controllable phasor.

Claim 9

A radar system carried aloft by aircraft for detecting long range and short range elevated targets while suppressing ground clutter, a system having a transmitter, and a receiver comprising: an antenna having at least two radiators; a first hybrid junction connected to the radiators for providing sum and difference return signals; a first circuit path including a duplexer connected between the first hybrid junction and a second hybrid junction for transmitting the sum signal therebetween; a second parallel circuit path connected between the first and second junctions and including a controllable attenuator for attenuating the difference signal, controllable phasor means connected to the output of the attenuator for selectively varying the phase shift of the attenuated difference signal, and a second duplexer connected to the output of the phasor means for coupling the phase shifted difference signal to the second hybrid junction; the function generator having outputs connected to inputs of the attenuator and phasor means for controlling the attenuator and the phasor means, respectively, in accordance with a beam steering program; height reference means connected to the function generator for making the beam steering program a function of antenna altitude; means connecting the transmitter to the function generator for making the beam steering program a function of target range; the sum and difference signals being combined at the second junction point to form a steered receive beam signal.

Claim 10

A radar system carried aloft by aircraft for detecting long range and short range elevated targets while suppressing ground clutter, a system having a transmitter, and a receiver comprising: an antenna having at least two radiators; a first hybrid junction connected to the radiators for providing sum and difference return signals; a first circuit path including a duplexer connected between the first hybrid junction and a second hybrid junction for transmitting the sum signal therebetween; a second parallel circuit path connected between the first and second junctions and including a controllable attenuator for attenuating the difference signal, controllable phasor means connected to the output of the attenuator for selectively varying the phase shift of the attenuated difference signal, and a second duplexer connected to the output of the phasor means for coupling the phase shifted difference signal to the second hybrid junction; the function generator having outputs connected to inputs of the attenuator and phasor means for controlling the attenuator and the phasor means, respectively, in accordance with a beam steering program; height reference means connected to the function generator for making the beam steering program a function of antenna altitude; means connecting the transmitter to the function generator for making the beam steering program a function of target range; the sum and difference signals being combined at the second junction point to form a steered receive beam signal.

Claim 11

The subject matter set forth in claim 3 together with frequency conversion means connected to the second junction for converting the steerable receive beam signal; and means for displaying information received at the antenna, the displaying means having a first input connected to the transmitter for providing display timing signals, a second input for providing a signal responsive to the angular orientation of the antenna, and a third input connected to the frequency conversion means for providing target information to the display means.

Claim 12

a function generator coupled to an altitude reference and to said controllable attenuator and said controllable phasor for generating said beam steering program;

Claim 13

a function generator coupled to an altitude reference and to said controllable attenuator and said controllable phasor for generating said beam steering program;

Claim 14

second circuit means including series connected mixer, amplifier and detector for deriving substantially clutter free information regarding said elevated targets from said receive antenna means;

Claim 15

second circuit means including series connected mixer, amplifier and detector for deriving substantially clutter free information regarding said elevated targets from said receive antenna means;

Claim 16

display means coupled to said second circuit means for displaying said signal derived from said antenna means.

Claim 17

display means coupled to said second circuit means for displaying said signal derived from said antenna means.