Image beam lock-on detector

Claim 2

In a radar system including oscillator means producing a transmitting signal, antenna means coupled to the oscillator means for providing a plurality of individually selectable beams aimed in different directions for transmission and receipt of energy, an unsuppressed image beam corresponding to one of the beams being present when another beam is selected, and tracking means coupled to the antenna means for locking onto the peak power frequency in the received energy for each selected beam to provide an output replica thereof, a method of detecting whether the tracking means is incorrectly locked onto the peak power frequency in the received energy of an unsuppressed image beam instead of a selected beam, comprising the steps of determining the maximum and minimum signal levels received by all of the selected beams, comparing the maximum level to the minimum level to obtain a beam signal level difference signal, and generating an alarm when the difference signal exceeds a predetermined level.

Claim 3

The method of claim 1 wherein the predetermined level represents the inherent image beam rejection of the antenna means.

Claim 4

A multi-beam doppler radar system of the type comprising a transmit-receive antenna adapted to be unmovably mounted on an aircraft providing a plurality of individually selectable beams aimed in different directions, a timing unit connected to the antenna to select the beams one at a time in a repeating sequence, an unsuppressed image beam of one of the beams being present when another beam is selected, an oscillator providing the antenna with a transmitting signal, a doppler shift detector coupled to the antenna and operatively receiving the transmitting Signal for extracting doppler signal spectra received in each beam, and frequency tracking means connected to receive the output of the doppler shift detector for locking onto the peak power frequency in the spectra and providing an output replica thereof, wherein the improvement comprises: beam power differential detector means operatively connected to said tracking means for determining the maximum and minimum levels of the peak power doppler signals returned in all of the beams and providing an output indicative of the difference between said maximum and minimum levels; and comparator means connected to receive the differential detector means output for providing an alarm signal when said detector means output exceeds a predetermined threshold indicative of lock onto an image beam by said tracking means.

Claim 5

A multi-beam doppler radar system of the type comprising a transmit-receive antenna adapted to be unmovably mounted on an aircraft providing a plurality of individually selectable beams aimed in different directions, a timing unit connected to the antenna to select the beams one at a time in a repeating sequence, an unsuppressed image beam of one of the beams being present when another beam is selected, an oscillator providing the antenna with a transmitting signal, a doppler shift detector coupled to the antenna and operatively receiving the transmitting Signal for extracting doppler signal spectra received in each beam, and frequency tracking means connected to receive the output of the doppler shift detector for locking onto the peak power frequency in the spectra and providing an output replica thereof, wherein the improvement comprises: beam power differential detector means operatively connected to said tracking means for determining the maximum and minimum levels of the peak power doppler signals returned in all of the beams and providing an output indicative of the difference between said maximum and minimum levels; and comparator means connected to receive the differential detector means output for providing an alarm signal when said detector means output exceeds a predetermined threshold indicative of lock onto an image beam by said tracking means.

Claim 6

The system of claim 3 wherein the improvement further comprises the tracking means providing an output signal indicative of the power of the signal beam tracked, said differential detector means including differential amplifier means having a first input connected to a source of reference voltage and a second input inverter means responsive to said power output of said tracking means for providing an output signal to said differential amplifier second input inversely proportional to said power output, a capacitive element operatively connected to receive the output of said amplifier for accumulating charge therefrom, diode means connected between said amplifier output and said capacitive element permitting current to flow to said capacitive element only when said reference voltage exceeds the voltage on said second input, and a feedback loop operatively connecting said capacitive element with the second input of said amplifier, said differential detector means difference output being provided by said second input of said amplifier.

Claim 7

The system of claim 4 wherein the improvement further comprises AGC means connected to receive said power signal from said tracking means and providing a control output to said inverter means.

Claim 8

The system of claim 5 wherein the improvement further comprises said AGC means including an AGC detector connected to receive said tracking means power output and multiplexed integrator means receiving the AGC detector output for providing said AGC means control output.

Claim 9

The system of claim 6 wherein the improvement further comprises said multiplexed integrator means including an AGC amplifier having an input connected to receive said AGC detector output, a plurality of capacitive elements corresponding respectively to the antenna beams, and a switching network responsive to the timing unit for connecting selected ones of said capacitive elements in parallel across the output and said input of said AGC amplifier, said AGC amplifier output providing the control output.

Claim 10

The system of claim 7 wherein the improvement further comprises said AGC means further including an attenuator responsive to said AGC amplifier output and connected to said doppler shift detector output for passing to said tracking means the shift detector output attenuated in accordance with said AGC amplifier output.

Claim 11

The system of claim 8 wherein the improvement further comprises said comparator means including threshold detector means receiving said difference output from said differential detector means and having a reference voltage for providing said alarm output signal when said reference voltage is exceeded by said difference output.

Claim 12

The system of claim 9 wherein the improvement further comprises said inverter means including transistor means having a gate input coupled to receive said tracking means power signal and a pair of terminals one of which is grounded and the other connected to said second input of said differential amplifier.

Claim 13

The system of claim 10 wherein the improvement further comprises said attenuator including a transistor element having a gate input and a pair of terminals, said gate input Being connected to receive said AGC amplifier output, one of said terminals being coupled to ground and the other being connected to said doppler shift detector output to ground out a variable portion thereof.

Claim 14

The system of claim 11 wherein the improvement further comprises said attenuator transistor element and said beam power differential detector transistor element being matched field effect transistors.

Claim 15

The system of claim 12 wherein the improvement further comprises means connected to said differential amplifier to inhibit the output thereof during beam switching responsive to the timing unit.