Method of measuring the altitude of a target maneuvering at a very low elevation, and a tracking radar using same

Claim 3

A method as defined in claim 1 wherein measured voltages representing said deviation signal and said quadrature component are averaged in each of said overlapping series over a number N of successive sampling frequencies, less than the total number of sampling frequencies in said pass band, said mean values being respectively represented by ##EQU15## wherein E i , E m , DQ i , DQ m are, respectively, the mean value of the voltage representing said deviation signal, the instantaneous value of a voltage representing said deviation signal at a frequency m, the mean value of the voltage representing said quadrature component, and the instantaneous value of the voltage representing said quadrature component at the frequency m.

Claim 4

A method as defined in claim 2 wherein the values representing the mean deviation signal E i and the mean quadrature component DQ i are derived from differently weighted voltages representing the instantaneous values of the voltages and, respectively.

Claim 5

A method as defined in claim 2 wherein the detection of said extreme point includes the steps of algebraically summing the last 2p instantaneous values of voltages obtained from successive measurements of said quadrature component, weighting the algebraic sums of the last p instantaneous values and of the immediately preceding p instantaneous values with coefficients of opposite sign, and monitoring a change in sign of the difference between said algebraic sums.

Claim 6

A method as defined in claim 4 wherein said weighting coefficients are +1 and -1.

Claim 7

A method as defined in claim 1 wherein said quadrature component is obtained by shifting by π/2 the phase of said difference signal and by demodulating the phase-shifted difference signal with respect to the vector of said sum signa.

Claim 8

A tracking radar of monopulse type for acertaining the altitude of a target, maneuvering at very low elevation, by processing reflected energy constituting a sum signal and a difference signal, said difference signal having an in-phase component colinear with said sum signal and a quadrature component perpendicular to said sum signal, comprising: a first and a second channel for respectively processing said sum signal and said difference signal; a third channel in parallel with said second channel including a π/2 phase shifter for processing the quadrature component of said difference signal; a first demodulator with input connections to said first and second channels for deriving from the ratio of said difference and sum signals a deviation signal proportional to an angular aiming error between the direction of said target and an aiming axis of the radar at an operating frequency thereof; a second demodulator with input connections to said first and third channels for delivering a signal voltage representing said quadrature component; oscillator means for successively generating a multiplicity of different operating frequencies within a predetermined pass band, said channels being provided with mixer means connected to said oscillator means; first filter means connected to said first demodulator for smoothing short-term variations of said deviation signal to provide a frequency-dependent error signal; second filter means connected to said second demodulator for smoothing short-term variations of said signal voltage, thereby producing a resulting voltage varying with said operating frequencies; validating means connected to said second filter means for detecting an extreme value of said resulting voltage; and output means connected to said first filter means and to said validating means for passing said error signal upon the occurrence of said extreme value.

Claim 9

A tracking radar of monopulse type for acertaining the altitude of a target, maneuvering at very low elevation, by processing reflected energy constituting a sum signal and a difference signal, said difference signal having an in-phase component colinear with said sum signal and a quadrature component perpendicular to said sum signal, comprising: a first and a second channel for respectively processing said sum signal and said difference signal; a third channel in parallel with said second channel including a π/2 phase shifter for processing the quadrature component of said difference signal; a first demodulator with input connections to said first and second channels for deriving from the ratio of said difference and sum signals a deviation signal proportional to an angular aiming error between the direction of said target and an aiming axis of the radar at an operating frequency thereof; a second demodulator with input connections to said first and third channels for delivering a signal voltage representing said quadrature component; oscillator means for successively generating a multiplicity of different operating frequencies within a predetermined pass band, said channels being provided with mixer means connected to said oscillator means; first filter means connected to said first demodulator for smoothing short-term variations of said deviation signal to provide a frequency-dependent error signal; second filter means connected to said second demodulator for smoothing short-term variations of said signal voltage, thereby producing a resulting voltage varying with said operating frequencies; validating means connected to said second filter means for detecting an extreme value of said resulting voltage; and output means connected to said first filter means and to said validating means for passing said error signal upon the occurrence of said extreme value.

Claim 10

A tracking radar as defined in claim 7 wherein said first filter means comprises an integrating network including a series inductance and a shunt capacitance.

Claim 11

A tracking radar as defined in claim 7 wherein said validating means comprises a differential amplifier with two inputs respectively connected to said first filter means by a direct path and by a delay line.

Claim 12

A tracking radar as defined in claim 7 wherein said oscillator means comprises a frequency synthesizer.

Claim 13

A tracking radar as defined in claim 7 wherein said output means comprises a differentiation circuit connected to said validating means for producing a trigger pulse derived from said resulting voltage upon a change in the polarity of said resulting voltage, a delay network connected to said first filter means, and a normally blocked gate in series with said delay network controlled by said trigger pulse for conducting upon a triggering of the latter.

Claim 14

A tracking radar as defined in claim 11 wherein said output means further comprises a monostable circuit connected to said differentiation circuit for actuation by said trigger pulse, said gate having a control input connected to said monostable circuit.

Claim 15

A tracking radar as defined in claim 7 wherein said first, second and third channels include respective first, second and third intermediate-frequency amplifiers downstream of said mixer means, further comprising automatic-gain-control means connected in parallel with said first and second demodulators to said first channel for generating a first control voltage for said first and second intermediate-frequency amplifiers and a second control voltage of half the dynamic range of said first control voltage for said third intermediate-frequency amplifier.

Claim 16

A tracking radar as defined in claim 13 wherein said automatic-gain-control means includes a first operational amplifier receiving said first control voltage, a voltage divider in series with a blocking capacitor in an output of said first operational amplifier, and a second operational amplifier having an input connected to a tap of said voltage divider for producing said second control voltage.