US3774206A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Pseudo-randomly phase modulated radar altimeter
Assignee: CMC Electronics Inc
•
Filing: 1971-08-16
•
Granted: 1973-11-20
•
Expires: 1991-08-16
Abstract
Abstract This invention relates to a pseudo-randomly phase modulated radar altimeter wherein the phase of a CW wave is shifted between 0* and 180* in a pseudo-random fashion by a modulation code generator prior to transmission, and a reflected wave is demodulated in the same way by a tracking code generator which provides a code identical to the modulation code generator code. A feature of the invention is that, in order to provide a selftest facility a digitally simulated delay is provided. The performance monitoring facility takes cognizance of the fact that, when the receiver is tracking, a closed loop is formed and that, in a closed loop, a perturbation introduced at one point will travel all around the loop. In the system, a perturbation is introduced at one point in the loop and a second point in the loop is examined for the presence or absence of the perturbation. The relative delay between the modulation code generator and the tracking code generator is indicative of the travel time of a reflected wave. In order to translate this data to useful information, a pulse is provided from the generators to different inputs of a flip-flop when the generators pass all ones state (or any other preselected state). The output of the flip-flop is then a train of pulses whose duty cycle is proportional to the relative delay between generators. Acquisition is effected by providing zero relative delay between the generators at the start. The tracking code generator is then automatically delayed by one clock pulse periodically. The automatic delay is terminated when the relative delay between the generators is equal to the two-way travelling time of a reflected signal, i.e. the system begins to track.
Inventors
- 👤 S Rauch
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 12:25
CPC Classifications
G; G01; G01S; G01S13/00; G01S13/02; G01S13/06; G01S13/08; G01S13/32; G01S13/325; G01S13/88; G01S13/882
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
453 words
A pseudo-randomly phase modulated radar altimeter comprising; a transmitter unit consisting of; a source of RF energy for providing a CW RF signal and comprising an output terminal; a phase modulator for phase modulating said RF signal and comprising an output terminal, RF input terminal means and modulation signal input terminal means; said RF input terminal means being fed from the output terminal of said RF source; said modulation signal input terminal means being fed from output terminal means of a modulation code generator; said modulation code generator providing a pseudo-random series of pulses and spaces; further comprising an input terminal fed from an output terminal of a clock oscillator providing clock pulses at a first frequency; said phase modulator being adapted to change the phase of said CW RF signal by 180* upon reception of the onset and completion of a pulse; and a receiver unit consisting of: an RF receiving portion having an input terminal and an output terminal; mixer means for converting the received RF signal to an IF signal and having two input terminals and an output terminal; one of said mixer input terminals being fed from the output of said RF receiving portion output terminal; the other of said mixer input terminals being fed from an output terminal of an offset generator; a tracking code generator having an input terminal and two output terminals; the signals at said tracking code modulator output terminals being identical with the exception that one output signal is time delayed relative to the other output signal; phase demodulator means comprising Means for receiving said tracking code modulator outputs in two channel operation, an input terminal fed from the output terminal of said mixer, and output means for providing a two channel output, each channel providing a variable level output signal; subtraction means comprising input means adapted to receive said two channel output and to provide an output at an output terminal thereof dependant upon the difference in levels of said two channels; loop filter means having an input terminal and an output terminal; the input terminal of said loop filter means being fed with the output of said subtraction means; voltage controlled oscillator means having a control signal terminal and an output terminal; said voltage controlled oscillator control terminal being fed from the output of said loop filter; and means for connecting the output terminal of said voltage controlled oscillator means to the input terminal of said tracking code modulator under predetermined conditions; said tracking code generator, phase demodulator means, subtraction means, loop filter means and voltage controlled oscillator comprising a loop; the tracking code modulator and the modulation code generator being so constructed as to produce identical codes at the outputs thereof.
Claim 2
Dependent Claim
453 words
A pseudo-randomly phase modulated radar altimeter comprising; a transmitter unit consisting of; a source of RF energy for providing a CW RF signal and comprising an output terminal; a phase modulator for phase modulating said RF signal and comprising an output terminal, RF input terminal means and modulation signal input terminal means; said RF input terminal means being fed from the output terminal of said RF source; said modulation signal input terminal means being fed from output terminal means of a modulation code generator; said modulation code generator providing a pseudo-random series of pulses and spaces; further comprising an input terminal fed from an output terminal of a clock oscillator providing clock pulses at a first frequency; said phase modulator being adapted to change the phase of said CW RF signal by 180* upon reception of the onset and completion of a pulse; and a receiver unit consisting of: an RF receiving portion having an input terminal and an output terminal; mixer means for converting the received RF signal to an IF signal and having two input terminals and an output terminal; one of said mixer input terminals being fed from the output of said RF receiving portion output terminal; the other of said mixer input terminals being fed from an output terminal of an offset generator; a tracking code generator having an input terminal and two output terminals; the signals at said tracking code modulator output terminals being identical with the exception that one output signal is time delayed relative to the other output signal; phase demodulator means comprising Means for receiving said tracking code modulator outputs in two channel operation, an input terminal fed from the output terminal of said mixer, and output means for providing a two channel output, each channel providing a variable level output signal; subtraction means comprising input means adapted to receive said two channel output and to provide an output at an output terminal thereof dependant upon the difference in levels of said two channels; loop filter means having an input terminal and an output terminal; the input terminal of said loop filter means being fed with the output of said subtraction means; voltage controlled oscillator means having a control signal terminal and an output terminal; said voltage controlled oscillator control terminal being fed from the output of said loop filter; and means for connecting the output terminal of said voltage controlled oscillator means to the input terminal of said tracking code modulator under predetermined conditions; said tracking code generator, phase demodulator means, subtraction means, loop filter means and voltage controlled oscillator comprising a loop; the tracking code modulator and the modulation code generator being so constructed as to produce identical codes at the outputs thereof.
Claim 3
Dependent Claim
42 words
A pseudo-randomly phase modulated radar altimeter as defined in claim 1 wherein said modulation code generator and said tracking code generator comprise identical maximal length shift registers and wherein the delay between said tracking code generator outputs is equal to one bit.
Claim 4
Dependent Claim
215 words
A pseudo-randomly phase modulated radar altimeter as defined in claim 2 wherein said subtraction means comprises; an envelope detector having an input terminal and an output terminal; said envelope detector input terminal being fed with the output of said phase demodulator means; a bandpass filter having an input terminal fed from the output terminal of said envelope detector and an output terminal; a synchronous switch having an input terminal fed from the output terminal of said bandpass filter, a reference signal terminal, and an output terminal; said loop filter input terminal being fed from the output terminal of said synchronous switch; and further comprising a time sharing gate having two input terminals, an output terminal and a switching rate control terminal; said two input terminals being fed, respectively, from the two output terminals of said tracking code generator; said output terminal being fed to an input terminal of said phase demodulator; and means for providing a switching control signal for opening said time sharing gate alternately to signals on said two output terminals of said tracking code generator at a switching rate frequency, said switching control signal means having an output terminal fed in parallel to the switching rate control terminal of said time sharing gate and said reference signal terminal of said synchronous switch.
Claim 5
Dependent Claim
40 words
A pseudo-randomly phase modulated radar altimeter as defined in claim 3 wherein said switching control signal means comprises a frequency counter having an input terminal, fed from a third output terminal of said tracking code generator, and three output terminals.
Claim 6
Dependent Claim
64 words
A pseudo-randomly phase modulated radar altimeter as defined in claim 4 and further comprising a delay compensation network having an input terminal and an output terminal; the input terminal of said delay compensation network being fed from one output terminal of said frequency counter; the reference signal terminal of said synchronous switch being fed from said one output terminal of said delay compensation network.
Claim 7
Dependent Claim
380 words
A pseudo-randomly phase modulated radar altimeter as defined in claim 5 and further comprising; an acquisition gate having three input terminals and an output terminal; a blanking gate having two input terminals and an output terminal; performance monitor means having an output terminal; and means for detecting a tracking condition in the receiver portion having an input terminal and an output terminal; the output terminal of said clock oscillator being fed to one input terminal of said blanking gate; means for periodically blanking said blanking gate being fed to the other input terminal of said blanking gate; the output terminal of said blanking gate being fed to one input terminal of said acquisition gate; the output terminal of said performance monitor means being fed to a second terminal of said acquisition gate; the output terminal of said voltage controlled oscillator means being fed to the third input terminal of said acquisition gate; the output terminal of said acquisition gate being fed to the input terminal of said tracking code generator; whereby, to initiate acquisition, a clocking pulse is provided by said clock oscillator to both said modulation code generator and, through said blanking gate and said acquisition gate, to said tracking code generator; the periodic blanking of said blanking gate preventing a pulse from said clock oscillator from reaching said tracking code generator to thereby provide a relative delay between said modulating code generator and said tracking code generator; the blanking continuing periodically until said relative delay is equal to the travel time between said radar and a target, whereupon said means for detecting a tracking condition will detect a tracking condition; said means for detecting a tracking condition providing a pulse to said acquisition gate to open said gate to said voltage controlled oscillator means and to close it to said clock oscillator when a tracking condition is detected so that the clocking pulse to said tracking code generator will be supplied by said voltage controlled oscillator means; the output of said loop filter under tracking conditions being substantially zero volts DC; said voltage controlled oscillator means being such that, when zero volts DC is applied to its signal control terminal, the frequency of said voltage controlled oscillator means is substantially equal to the frequency of said clock oscillator.
Claim 8
Dependent Claim
248 words
A pseudo-randomly modulated radar altimeter as defined in claim 5 and further comprising; a transmitting antenna; output means connecting the output of said phase modulator to said transmitting antenna; a receiving antenna; input means connecting the receiving antenna to said input terminal of said mixer, said input means comprising a first switch having a control signal terminal; means coupling said input means to said output means, said coupling means comprising a second switch having a control signal terminal; a self-test gate having input terminal means, a control signal terminal and an output terminal; and self-test signal means having an output terminal; the output terminal of said self-test signal means being fed to the control signal terminals of said first switch, said second switch and said self-test gate; said switches being arranged such that, when said first switch is open said second switch is closed and vice-versa; said input terminal means of said self-test gate being fed from said output terminal means of said modulation code generator; said output terminal of said self-test gate being fed to said input terminal means of said phase modulator; the switches and self-test gate arrangement being such that, when a signal is applied from said self-test signal means, said first switch is opened and said second switch is closed whereby the transmitter is coupled directly to the receiver and the receiver is uncoupled from said receiver antenna, and said self-test gate generates a relative predetermined delay between a transmit and a receive code.
Claim 9
Dependent Claim
289 words
A pseudo-randomly phase modulated radar altimeter as defined in claim 5 wherein said loop filter comprises a further input terminal, and further comprising; means for generating a perturbing signal at a very low frequency and having an output terminal; a second delay compensation means having an input terminal and an output terminal; a second synchronous switch having an input terminal, a reference signal terminal and an output terMinal; a first low pass filter having an input terminal and an output terminal; and a second low pass filter having an input terminal and an output terminal; the output terminal of said perturbing signal generating means being fed to said further input terminal of said loop filter and said input terminal of said second delay compensation network; the output terminal of said second delay compensation network being fed to the reference signal terminal of said second synchronous switch; the output terminal of said subtraction means being fed to the input terminal of said first low pass filter; the output terminal of said first low pass filter being fed to the input terminal of said second synchronous switch; the output terminal of said second synchronous switch being fed to the input terminal of said second low pass filter; said first low pass filter being adapted to pass frequencies at and below said very low frequency and said second low pass filter being adapted to pass substantially only the DC component at the output of said second synchronous switch; whereby a perturbing signal is introduced into the loop at the loop filter and the performance of the loop is monitored by examining the effect of the perturbing signal on the loop at the ouput of the subtraction means in the second synchronous switch.
Claim 10
Dependent Claim
189 words
A pseudo-randomly phase modulated radar altimeter as defined in claim 5 and further comprising; a flip-flop means having a first input terminal, a second input terminal and an output terminal; and an integrator means having an input terminal and an output terminal; said first input terminal of said flip-flop means being fed from a second output terminal of said modulation code generator and said second input terminal of said flip-flop being fed from a second output terminal of said tracking code generator; the output terminal of said flip-flop means being fed to the input terminal of said integrator; the output terminal of said integrator being fed to a display means; the tracking code generator and the modulation code generator being adapted to provide a signal to the respective flip-flop input terminals when each reaches a same predetermined position in the codes thereof; whereby, the output of the flip-flop will be a pulse train whose duty cycle is proportional to the relative delay between the tracking code generator and modulation code generator codes; and the output of said integrator is an analogue signal whose level is proportional to said delay.
Claim 11
Dependent Claim
248 words
A pseudo-randomly modulated radar altimeter as defined in claim 6 and further comprising; a transmitting antenna; output means connecting the output of said phase modulator to said transmitting antenna; a receiving antenna; input means connecting the receiving antenna to said one input terminal of said mixer, said input means comprising a first switch having a control signal terminal; means coupling said input means to said output means, said coupling means comprising a second switch having a control signal terminal; a self-test gate having input terminal means, a control signal terminal and an output terminal; and self-test signal means having an output terminal; the output terminal of said self-test signal means being fed to the control signal terminals of said first switch, said second switch and said self-test gate; said switches being arranged such that, when said first switch is open said second switch is closed and vice-versa; said input terminal means of said self-test gate being fed from said output terminal means of said moudlation code generator; said output terminal of said self-test gate being fed to said input terminal means of said phase modulator; the switches and self-test gate arrangement being such that, when a signal is applied from said self-test signal means, said first switch is opened and said second switch is closed whereby the transmitter is coupled directly to the receiver and the receiver is uncoupled from said receiver antenna, and said self-test gate generates a relative predetermIned delay between the transmit and receive codes.
Claim 12
Dependent Claim
316 words
A pseudo-randomly phase modulated radar altimeter as defined in claim 10 wherein said loop filter comprises a further input terminal, and wherein said frequency counter is adapted to provide a perturbing signal at a very low frequency at its third output terminal; and further comprising; a second delay compensation means having an input terminal and an output terminal; a second synchronous switch having an input terminal, a reference signal terminal and an output terminal; a first low pass filter having an input terminal and an output terminal; and a second low pass filter having an input terminal and an output terminal; said perturbing signal being fed to said further input terminal of said loop filter and said input terminal of said second dealy compensation network; the output terminal of said second delay compensation network being fed to the reference signal terminal of said second synchronous switch; the output terminal of said first synchronous switch being fed to the input terminal of said first low pass filter; the output terminal of said first low pass filter being fed to the input terminal of said second synchronous switch; the output terminal of said second synchronour switch being fed to the input terminal of said second low pass filter; said first low pass filter being adapted to pass frequencies at and below said very low frequency and said second low pass filter being adapted to pass substantially only the DC component at the output of said second synchronous switch; whereby a perturbing signal is introduced into the loop at the loop filter and the performance of the loop is monitored by examining the effect of the perturbing signal on the loop at the output of the first synchronous switch in the second synchronous switch; said first low pass filter, second synchronous switch, second low pass filter and second delay compensation network comprising said means for detecting a tracking condition.
Claim 13
Dependent Claim
189 words
A pseudo-randomly phase modulated radar altimeter as defined in claim 11 and further comprising; a flip-flop means having a first input terminal, a second input terminal and an output terminal; and an integrator means having an input terminal and an output terminal; said first input terminal of said flip-flop means being fed from a second output terminal of said modulation code generator and said second input terminal of said flip-flop being fed from a second output terminal of said tracking code generator; the output terminal of said flip-flop means being fed to the input terminal of said integrator; the output terminal of said integrator being fed to a display means; the tracking code generator and the modulation code generator being adapted to provide a signal to the respective flip-flop input terminals when each reaches a same predetermined position in the codes thereof; whereby, the output of the flip-flop will be a pulse train whose duty cycle is proportional to the relative delay between the tracking code generator and modulation code generator codes; and the output of said integrator is an analogue signal whose level is proportional to said delay.
Claim 14
Dependent Claim
28 words
A pseudo-randomly phase modulated radar altimeter as defined in claim 12 comprising two identical altimeter systems each being adapted to be operated at a different clock oscillator frequency.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-11-19 | 1977-05-21 | 1977-11-20 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-11-19 | 1981-05-21 | 1981-11-20 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-11-19 | 1985-05-21 | 1985-11-20 | $7700.00 | Window Closed / Lapsed |