MULTIFREQUENCY CW RADAR WITH RANGE CUTOFF

• US 3,750,172 A
• Filed: 06/02/1971
• Issued: 07/31/1973
• Est. Priority Date: 06/02/1971
• Status: Expired due to Term

• Current Assignee: Carl P. Tresselt
• Original Assignee: Carl P. Tresselt
• Inventors: Tresselt, Carl P.
• Primary Examiner(s): Hubler, Malcolm F.
• Application Number:
  US05/149,265
• Time in Patent Office: 790 Days
• Field of Search: 343/9,12R
• US Class Current: 342/129
• CPC Class Codes: G01S 13/348 using square or rectangular modulation, e.g. diplex radar for ranging over short distances
• CPC Class Codes: G01S 13/50 Systems of measurement based on relative movement of target

Abstract

This invention is directed to a CW radar system having range cutoff capability to render it insensitive to targets beyond a preselected range. Three frequencies are sequentially transmitted and reflections from a relatively moving target received to produce three doppler frequencies. The doppler shifts on the highest and lowest transmitted frequencies are phase compared to indicate range between the target and the antenna, which is unambiguous out to a preselected range. By noting the leadinglagging relationship of these two doppler frequencies, phase can be used below the ambiguous range to indicate whether the target is approaching or receding from the antenna. The third transmitted frequency lies between the other two, and produces an additional doppler frequency which can be phase compared with either of the other two doppler signals. Since the carrier frequency difference is lower in this latter comparison, the ambiguity in indicated range will occur at a greater distance. The lower difference frequency can accordingly be used to generate an inhibit signal for targets which fall near or beyond the ambiguity point of the first, higher deviation range measurement channel. Alternately, the third doppler can be phase compared with both of the other two and the results averaged for signal-to-noise ratio improvement. The average long range thus obtained is then used to generate the long-range inhibit signal when the average long-range value is beyond the preselected range.

Claims

1. A doppler syStem capable of generating an inhibit signal in response to targets beyond a preselected range comprising:

means for sequentially generating signals of at least three carrier frequencies;

means for transmitting said signals and receiving reflected signals from a target having a relative velocity with respect to said means for transmitting, the reception of said reflected signals resulting in the production of a doppler signal for each signal transmitted;

gating means for individually gating each of said doppler signals to a doppler channel so that separate doppler signals are present as outputs from said channels;

first phase detector means simultaneously receiving a first two of said doppler signals and producing a range signal indicative of the range between said target and said means for transmitting;

second phase detector means receiving another two of said doppler signals and producing an output useful as said inhibit signal.

2. The system of claim 1 wherein there are three of said signals generated so that three doppler signals are produced;

said first phase detector receives the doppler signals corresponding to the highest and lowest of said transmitted frequencies as said first two dopplers; and

said second phase detector receives one of said first two doppler signals and the other of said dopplers to produce said inhibit signal.

3. The system of claim 1 wherein the transmitted frequencies resulting in said first two doppler signals are separated by a preselected frequency range and the transmitted frequencies resulting in said another two dopplers are separated by a second frequency range less than said preselected frequency range.

4. The system of claim 3 wherein three of said signals are transmitted so that three doppler signals are produced, the transmitted frequencies resulting in said first two doppler signals constituting the highest and lowest of said transmitted frequencies and the transmitted frequencies resulting in said another two doppler signals constituting one of said first two and the third of said transmitted frequencies.

5. The system of claim 4 wherein the transmitted frequency resulting in said third doppler signal lies midway between the transmitted frequencies resulting in said highest and lowest doppler signals.

6. The system of claim 3 wherein said second frequency range is one half of said preselected frequency range.

7. The system of claim 2 wherein the transmitted frequency resulting in said other of said dopplers is midway between the transmitted frequencies resulting in said highest and lowest dopplers.

8. The system of claim 1 wherein said gating means includes gating voltage generating means for individually opening said doppler channels during the transmission of said transmitted signals so that said doppler signals are properly received by said first and second phase detectors.

9. The system of claim 8 wherein said doppler channels are opened only during the last half of the time the corresponding transmitted signal is transmitted.

10. The system of claim 4 wherein said gating means includes gating voltage generating means for opening said doppler channels so that said doppler signals are properly directed to said channels, the first of said channels being open only during the last portion of the transmission period of the first of said frequencies;

the second of said channels being open only during the last portion of the transmission period of the second of said frequencies, and the third of said channels being open only during the last portion of the transmission period of the third of said frequencies.

11. The system of claim 10 wherein said last portions are the last one half of the transmission periods.

12. The system of claim 1 wherein said means for generating is a voltage responsive oscillator.

13. The system of claim 12 wherein said gating means includes means for varying the voltage applied to said oscillator so that said at least three frequencies are generated.

14. The system of claim 13 wherein said gating means includes gating voltage generating means for individually opening said doppler channels during the transmission of said transmitted signals.

15. The system of claim 14 wherein said doppler channels are opened only during a portion of the time the corresponding transmitted signal is transmitted.

16. The system of claim 15 wherein the transmitted frequencies resulting in said first two doppler signals are separated by a preselected frequency range and the transmitted frequencies resulting in said another two dopplers are separated by a second frequency range less than said preselected frequency range.

17. The system of claim 16 wherein three of said signals are transmitted so that three doppler signals are produced, said first two doppler signals corresponding to the highest and lowest of said transmitted signals and said another two doppler signals constituting one of said first two and the third of said transmitted signals.

18. The system of claim 17 wherein the transmitted frequency resulting in said third doppler signal lies midway between the transmitted frequencies resulting in said highest and lowest doppler signals;

and wherein said portion is the last half of each transmission period.

19. The system of claim 15 wherein said oscillator includes a device having a negative resistance characteristic.

20. The system of claim 18 wherein said oscillator includes a device having a negative resistance characteristic and a varactor;

said varactor receiving the voltage applied to said oscillator so that said at least three frequencies are generated.

21. The system of claim 1 further including a threshold circuit, said threshold circuit receiving the output of said second phase detector and generating said inhibit signal when the output of said second phase detector is above a preselected level.

22. The system of claim 3 further including a threshold circuit receiving the output of said second phase detector and generating said inhibit signal when the output of said second phase detector is above a preselected level.

23. The system of claim 11 further including a threshold circuit receiving the output of said second phase detector and generating said inhibit signal when the output of said second phase detector is above a preselected level.

24. The system of claim 19 further including a threshold circuit receiving the output of said second phase detector and generating said inhibit signal when the output of said second phase detector is above a preselected level.

25. A method of providing an inhibit signal beyond a preselected range in a doppler radar system including the steps of:

generating a plurality of at least three frequencies;

sequentially transmitting said frequencies as transmitted signals and receiving said frequencies as reflected signals;

producing a doppler signal for each transmitted signal by mixing a portion of the transmitted signal with the corresponding reflected signal of the same frequency;

individually gating each doppler signal to a separate doppler channel;

combining two of said doppler signals having a preselected frequency spread to produce a range signal; and

combining another two of said doppler signals having a frequency spread less than said preselected frequency spread to produce said inhibit signal.

26. The method of claim 25 wherein said step of transmitting includes the transmission of three frequencies so that three doppler signals are produced;

said combining step includes combining the extremity carrier frequency dopplers of said three dopplers to produce said range signal;

said step of combining another two dopplers includes combining one of said extremity carrier frequency dopplers and the third of said dopplers to produce said inhibit signal.

27. The method of claim 26 wherein said three frequencies are evenly spaced and said third doppler signal is the middle doppler signal.

28. The method of claim 27 wHerein said gating step includes gating said doppler channels so that each doppler gate is open only during the transmission of the transmitted frequency creating said doppler.

29. The method of claim 27 wherein said gating step includes gating said doppler channels during a portion of the time period that the corresponding frequency is transmitted.

30. The method of claim 29 wherein said portion is the last half of the transmission period.