FM-CW Radar ranging system

• US 4,106,020 A
• Filed: 07/21/1977
• Issued: 08/08/1978
• Est. Priority Date: 07/21/1977
• Status: Expired due to Term

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: RCA Corporation
• Inventors: Johnson, Henry C.
• Primary Examiner(s): Wilbur, Maynard R.
• Assistant Examiner(s): Berger, Richard E.
• Application Number:
  US05/817,686
• Time in Patent Office: 383 Days
• Field of Search: 343/14, 343/17.5
• US Class Current: 342/128
• CPC Class Codes: G01S 13/345 using triangular modulation

Abstract

A frequency-modulated continuous wave (FM-CW) ranging system includes apparatus which utilizes a target simulating delay line and scaling device to compensate for undesired changes of the FM modulation waveform.

Claims

1. In a frequency modulated continuous wave ranging system of the type including:

first means for generating a continuous wave interrogation signal, said interrogation signal being frequency modulated in accordance with a desired waveform having predetermined parameters enabling measurement of the range, R, of a target of interest, at least one of said parameters being subject to undesired changes in value which change the measured range;

second means for transmitting said interrogation signal to a target and receiving reflected signals from said target; and

third means for deriving difference signals indicative of the frequency difference of said reflected signals from the instantaneous frequency of said interrogation signal, said difference signals being indicative of said range;

the improvement comprising;

fourth means also responsive to said interrogation signal and said undesired changes therein for deriving difference signals indicative of the distance of a target at a known distance;

fifth means responsive to said difference signals from said third means for determining a parameter of the same representative of target range and responsive to the signals from said fourth means for scaling said parameter.

2. The combination as set forth in claim 1 wherein said fifth means is a digital counter responsive to said signal from said third means for counting cycles of the same and responsive to signals from said fourth means for resetting the same, the maximum count in said counter before it is reset being indicative of said range.

3. The combination as set forth in claim 1 wherein said fourth means includes a delay line simulating said target at said known distance.

4. The combination as set forth in claim 3 wherein said fourth means includes a directional coupler coupled between said delay line and said second means for passing said interrogation signals therebetween and also includes means coupled to said third means for passing signals, being said signals from said fourth means, relating to the distance simulated by said delay line.

5. The combination as set forth in claim 3 wherein said fourth means includes a first directional coupler coupled between said first means and said delay line for passing signals thereto and a second directional coupler between said delay line and third means for passing delayed signals to said third means and including means coupled to said third means for passing signals, being said signals from said fourth means relating to the distance simulated by said delay line.

6. The combination as set forth in claim 3 wherein said fourth means also includes a three port circulator, a mixer, a first directional coupler coupling between said source of interrogation signals and one port of said three port circulator, said delay line being coupled to a second port of said three port circulator for permitting bidirectional passage of signals therebetween and said mixer being coupled to the remaining port of said three port circulator to receive reflected signals from said delay line thereat, and wherein said fourth means also includes a second directional coupler coupled between said source of interrogation signals and said mixer, said mixer deriving difference signals indicative of a frequency difference of said reflected signals from said delay line and the instantaneous signal of said first means, said fourth means also including a divide-by-N circuit coupled to said mixer for producing a signal which is said signal from said fourth means.

7. In a frequency modulated continuous wave ranging system, comprising in combination:

means for generating a continuous wave interrogation signal, said interrogation signal being frequency modulated in accordance with a desired waveform having predetermined parameters enabling computation of the range, R, of a target of interest, at least one of said parameters being subject to undesired changes in value which change the computed range;

means for transmitting said interrogation signal to a real target at a distance within the range R₁ to R₂ and receiving reflected signals from said real target;

means for deriving difference signals indicative of the frequency difference of said reflected signals from the instantaneous frequency of said interrogation signal, said difference signals being indicative of said range of targets represented by said reflected signals;

means simulating a target at a known range not within said range R₁ to R₂ ;

means coupling said interrogation signal to said target simulating means and coupling the reflected signal therefrom to said means for deriving difference signals;

first and second bypass filters coupled to said means for deriving difference signals, said first bypass filter passing frequencies of said difference signal associated with said real target, said second bypass filter passing frequencies of said difference signal associated with said simulated target;

a divide-by-N circuit coupled to said second bandpass filter to produce a pulse for each N cycles of said frequency signal passed by said second bandpass filter; and

a counter means having count and reset terminals, wherein said first bandpass filter is coupled to said count terminal for advancing said counter for each cycle of signal passed by said first bandpass filter and wherein said divide-by-N circuit is coupled to the reset terminal of said counter for resetting the same by each said pulse, and wherein the maximum count in said counter before being reset represents the range of said real target.

8. The combination as set forth in claim 7 wherein said means to simulate a target is a delay line operating in the reflective mode and wherein said coupling means comprises solely a single directional coupler through which interrogation signals pass to said delay line and through which said reflected signals from said delay line pass to said means for deriving difference signals.

9. The combination as set forth in claim 7 wherein said means simulating target is a delay line operated in the transmission mode and wherein said coupling means comprises first and second directional couplers, said first directional coupler arranged to couple said interrogation signals to said delay line and said second directional coupler arranged to couple signals from said delay line to said means for deriving difference signals.

10. In a frequency modulated continuous wave ranging system, comprising in combination:

means for generating a continuous wave interrogation signal, said interrogation signal being frequency modulated in accordance with a desired waveform having predetermined parameters enabling computation of the range, R, of a target of interest, at least one of said parameters being subject to undesired changes in value which change the computed range;

means for transmitting said interrogation signal to a real target and receiving reflected signals from said real target;

first means for deriving difference signals indicative of the frequency difference of said reflected signals from the instantaneous frequency of said interrogation signal, said difference signals being indicative of said range of targets represented by said reflected signals;

means simulating a target at a known range;

means coupling said interrogation signal to said means for simulating a target and producing a delayed signal therefrom, delayed in accordance with the distance simulated by said target simulating means;

a second means receptive of said interrogation signal and of said delayed signal for deriving difference signals indicative of the frequency difference of said delayed signal from the instantaneous frequency of said interrogation signal, said difference signals produced thereby being indicative of the simulated range of said simulated target;

a divide-by-N circuit coupled to said second means for deriving a difference signal for producing a pulse for each N cycles from said second means;

a counter means having count and reset terminals wherein said first means for deriving difference signals is coupled to said count terminal for advancing said counter for each cycle of the signal produced by said first means and wherein said divide-by-N circuit is coupled to the reset terminal of said counter means for resetting the same by each said pulse and wherein the maximum count in said counter represents the range of said real target.

11. The combination as set forth in claim 10 wherein said means simulating a target is a delay line arranged to operate in the reflective mode.