MODULATION CORRELATED FM RANGING SYSTEM

• US 3,623,097 A
• Filed: 07/17/1969
• Issued: 11/23/1971
• Est. Priority Date: 07/17/1969
• Status: Expired due to Term

• Current Assignee: Raymond H. Femenias
• Original Assignee: Raymond H. Femenias
• Inventors: Femenias, Raymond H.
• Primary Examiner(s): Tubbesing, T. H.
• Application Number:
  US04/842,479
• Time in Patent Office: 859 Days
• Field of Search: 343/14
• US Class Current: 342/128
• CPC Class Codes: G01S 13/345 using triangular modulation

Abstract

A modulation correlated FM ranging system for the detection and reliable indication of target presence and distance to target. The system utilizes cross-correlation and successive coherent detection techniques to provide a greatly improved signal-tonoise ratio at the receiver output in addition to the featured capability of coding against foreign signals. The system is insensitive to leakage effects and can range quantizing-effect free and ambiguity free while sacrificing neither transmitter bandwidth nor in-target observation time. The system also provides an optimal figure of merit for distance-measuring systems. In addition to distance measurement by frequency difference, the system incorporates a special time delay parameter which, when properly selected, allows a high correlation at the receiver output whenever a target is present in the target area.

Claims

1. A frequency-modulated system for use as a distance measuring device comprising, in combination:

a. signal-generating means for producing a voltage waveform for use as a modulating signal and as a reference signal, b. transmitting means responsive to said modulating signal for producing a frequency-modulated signal and propagating said frequency-modulated signal toward a target area, c. receiving means for receiving said frequency-modulated signal from said target area, d. frequency-comparing means for comparing the frequencies of said received signal and said transmitted signal and for producing A first output signal whose polarity is based on said comparison, e. correlating means for correlating said first output signal with said reference signal and producing a second output signal whenever a target is in the said target area.

2. The invention according to claim 1 wherein said signal-generating means comprises a generator for producing said voltage waveform, an integrator which integrates said voltage waveform to produce said modulating signal, and a limiter which acts on said voltage waveform to produce said reference signal.

3. The invention according to claim 1 wherein said transmitting means comprises a voltage-controlled oscillator which produces a carrier frequency output that is proportional to the voltage of said modulating signal.

4. The invention according to claim 1 wherein said correlating means comprises a delay circuit which imposes a selected time delay upon said reference signal, a multiplier circuit which produces the product of the said time-delayed reference signal with the said first output signal, and a smoothing filter which acts on said product to filter out noise signals and provide said second output according to the correlation between the two input signals.

5. The invention according to claim 1 wherein said voltage waveform comprises a waveform having a random instantaneous frequency.

6. A method of detection and indication of a target in a predetermined target area comprising the steps of:

a. generating a signal to be used as a modulating signal and as a reference signal, b. transmitting a frequency-modulated carrier signal in response to said modulating signal towards said predetermined target area, c. receiving said frequency-modulated carrier signal in the presence of said target in said predetermined target area, d. comparing the frequency of said received FM signal with the frequency of the transmitted FM signal to obtain a first output signal, e. time delaying said reference signal, f. correlating said time-delayed reference signal with said first output signal to obtain a second output signal.

7. The invention according to claim 6 wherein said modulating signal provides a probability of carrier frequency upswings of the same order of magnitude as the probability of frequency downswings.

8. The invention according to claim 6 wherein said first output signal is of a positive polarity when the frequency of the transmitted signal is higher than the frequency of the received signal and is of a negative polarity when the transmitted signal is of lower frequency than that of the received signal.

9. The invention according to claim 6 wherein said first output signal is a replica of said time-delayed reference signal wherever said target is present in the said target area.

10. The invention according to claim 6 wherein the time delay applied to said reference signal is equal to the one-way travel time of the transmitted signal to said target.

11. The invention according to claim 6 wherein said second output is a DC voltage whenever the said first output signal and the delayed reference signal correlate.