RANGE CUTOFF SYSTEM FOR DUAL FREQUENCY CW RADAR

• US 3,766,554 A
• Filed: 03/01/1971
• Issued: 10/16/1973
• Est. Priority Date: 03/01/1971
• Status: Expired due to Term

• Current Assignee: Carl P. Tresselt
• Original Assignee: Carl P. Tresselt
• Inventors: Tresselt, Carl P.
• Primary Examiner(s): Tubbesing, T. H.
• Application Number:
  US05/119,780
• Time in Patent Office: 960 Days
• Field of Search: 343/8,9,12R,14,17.5
• 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

A system for making a CW radar system insensitive to targets lying beyond a preselected maximum range is described. Two discrete frequencies are alternately transmitted so that two doppler frequencies are produced in the receiver. The phase relationship between the two doppler signals is indicative of the range between the target and transmitting antenna. Range cutoff is achieved by turning off the transmitter for an interval between the transmission of the two frequencies and by gating the homodyne receiver so that video output is provided only during the last quarter of each transmitted signal. Because the transmitter and receiver are inactive at chosen time intervals, complete receiver insensitivity is realized for targets beyond the cutoff range, irrespective of the size and other physical characteristics of the targets.

Claims

1. A range cutoff system for a dual frequency continuous wave radar system, said radar system having a variable output frequency transmitter so that at least two discrete frequencies, f1 and f2, are alternately transmitted and a two-channel receiver for producing two doppler frequencies fd1 and fd2 in response to the reception of reflections of said transmitted frequencies;

said range cutoff system including;

modulation means for modulating said transmitter so that said two frequencies f1 and f2 are alternately transmitted and said trasmitter produces no effective output for a preselected time period between the transmission of said frequencies f1 and f2.

2. The range cutoff system of claim 1 wherein said receiver further includes switching means for alternately actuating said two channels in synchronism with the transmission of said f1 and f2 frequencies;

and said modulation means modulates said switching means so that said channels are respectively responsive to received energy only during a portion of the time periods during which said f1 and f2 frequencies are respectively transmitted.

3. The range cutoff system of claim 1 wherein said transmitter includes a Gunn diode, said Gunn diode transmitting said f1 frequency when a first biasing voltage is applied, said f2 frequency when a second biasing voltage is applied, and no effective output when an off-voltage approximately equal to a third biasing voltage or less is applied;

sAid modulating means sequentially and cyclic providing biasing voltages in an order;

said first biasing voltage, said off-voltage, and said second biasing voltage and said off voltage again.

4. The range system of claim 3 wherein said receiver further includes switching means for alternately actuating said two channels in synchronism with the transmission of said f1 and f2 frequencies;

and said modulation means modulates said switching means so that said channels are respectively responsive to received energy only during a portion of the time periods during which said f1 and f2 frequencies are respectively transmitted.

5. The range cutoff system of claim 4 wherein said modulating means modulates said switching means only during the last one-fourth of said time periods.

6. The range cutoff system of claim 5 wherein said receiver includes amplifier-limiting means so that the relative range sensitivity is substantially flat up to a preselected range and rapidly drops to zero slightly above said preselected range.

7. The range cutoff system of claim 6 wherein said modulation means includes means for generating a clocking pulse train, said clocking pulse train forming a timing basis for the generation of said biasing voltages and having a period such that said preselected range is less than 300 feet.

8. The range cutoff system of claim 7 further including a varactor interposed between said modulation means and said Gunn diode so that said biasing voltages are applied to said Gunn diode through said varactor.

9. The range cutoff system of claim 1 wherein said frequency f1 is transmitted when a first control signal is applied to said transmitter, said frequency f2 is transmitted when a second control signal is applied to said transmitter, and no effective output is transmitted when a third control signal is applied to said transmitter;

and said modulating means includes means for sequentially and cyclically generating said first control signal, said third signal, said second control signal and said third signal again.

10. The range cutoff system of claim 9 wherein said modulating means generates first and second biasing voltages and an off-voltage approximately equal to or less than a third biasing voltage, wherein said first and second biasing voltages are said first and second control signals and said off-voltage is said third control signal.

11. The range cutoff system of claim 10 wherein said modulating means generates an off-voltage between 0 and slightly less than said third biasing voltage.

12. The range cutoff system of claim 10 wherein said modulating means generates and off-voltage slightly less than said third biasing voltage.

13. The range cutoff system of claim 10 wherein said modulating means generates an off-voltage between 0 and slightly more than said third biasing voltage.

14. The range cutoff system of claim 10 wherein said modulating means generates an off-voltage slightly higher than said third biasing voltage.

15. The range cutoff system of claim 9 wherein said variable output frequency transmitter includes a tuning element responsive to said modulating means for modulating the output frequency of said transmitter between said two frequencies f1 and f2;

said modulating means modulating said transmitter between a no effective output state and effective output states coincident with the transmission of said frequencies f1 and f2.

16. The range cutoff system of claim 15 wherein said tuning element is a varactor.

17. The range cutoff system of claim 15 wherein said tuning element is a ferrite material.

18. The range cutoff system of claim 14 wherein said tuning element is a PIN diode.

19. A method of providing range cutoff in a radar system having a multifrequency output transmitter for transmitting energy of varying frequencies in response to varying control signals and a multiChannel receiver for producing different doppler frequencies in response to the reception of said transmitted frequencies as reflected signals from targets including the steps of:

providing a first control signal to said transmitter so that a frequency f1 is transmitted, providing a second control signal to said transmitter so that no effective energy is transmitted, providing a third control signal to said transmitter so that a frequency f2 is transmitted, again providing said second control signal, and cyclic repeating the provision of all of said control signals.

20. The method of claim 19 including the step of:

switching said receiver between said channels so that a different channel is actuated for each of said transmitted frequencies; and

controlling said channels to be actuated only during a portion of the time period during which energy is transmitted.

21. The method of claim 20 wherein said step of controlling said channels, controls actuation of said channels only during the last one-quarter of said time period.

22. The method of claim 20 wherein said transmitter includes a Gunn diode having a characteristic of transmitting said frequency f1 when a first biasing voltage serves as said first control signal, transmitting no effective energy when an off-voltage approximately equal to or below a second biasing voltage serves as said control signal, and transmitting said frequency f2 when a third biasing voltage serves as said third control signal;

and including the steps of sequentially providing said first biasing voltage, providing said off-voltage, and providing said third biasing voltage so that no effective energy is transmitted after the transmission of each of said f1 and f2 frequencies.

23. The method of claim 22 wherein said step of controlling said channel controls the actuation of said channels only during the last one-quarter of said time period.

24. The method of claim 22 including the step of providing said off-voltage at a level between 0 and said third biasing voltage during the period when no energy is transmitted.

25. The method of claim 24 including the step of providing said off-voltage at a level slightly less than said third biasing voltage during the period when no energy is transmitted.

26. The method of claim 24 including the step of providing said off-voltage at a level slightly higher than said third biasing voltage during the period when no energy is transmitted.