System for generating simulated radar targets

• US 6,346,909 B1
• Filed: 09/06/2000
• Issued: 02/12/2002
• Est. Priority Date: 09/06/2000
• Status: Expired due to Fees

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: The United States Of America As Represented By The Secretary Of The Army
• Inventors: Johnson, James B. Jr., Connolly, Michael P.
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US09/656,194
• Time in Patent Office: 524 Days
• Field of Search: 342/165, 342/167, 342/169, 342/170, 342/171, 342/172, 342/173, 342/174, 434/2
• US Class Current: 342/169
• CPC Class Codes: G01S 13/767 Responders; Transponders teaching or practice apparatus for gun-aiming or gun-laying using reflecting targets or active targets F41G3/26
• CPC Class Codes: G01S 7/024 using polarisation effects in waveguides H01P1/165; for aerials H01Q, e.g. H01Q15/22, H01Q15/24, H01Q19/195
• CPC Class Codes: G01S 7/4052 by simulation of echoes
• CPC Class Codes: G01S 7/4082 using externally generated reference signals, e.g. via remote reflector or transponder

Abstract

A system is disclosed for generating simulated radar targets that eliminates the necessity for large outdoor test ranges and is relatively low in cost. The simulated radar target generating system provides complex targets of given simulated dimensions at given simulated distances when stimulated by signals emitted by the radar sensor in the sensor'"'"'s operational frequency. The dimensions are simulated by the use of multi-tap delay device while the distances (or, range) are simulated by routing the signal, in the form of light, through a fiber optic delay of a desired length. This system, which costs less than $50 thousand, can be located as close as eight feet to the sensor under test.

Claims

1. A system for generating simulated radar targets of pre-selected dimensions at pre-selected simulated distances for testing a radar sensor, the radar sensor having an operational frequency range, said radar target generator comprising:

a source of input radiation in the radar sensor'"'"'s operational frequency range;

a means for receiving said input radiation and, in response, producing intermediate frequency signal;

a means for simulating said pre-selected dimensions;

a means for simulating said pre-selected distances, said distance-simulating means being coupled between said intermediate-frequency producing means and said dimension simulating means;

a means for rendering said intermediate frequency into an output in the radar sensor'"'"'s operational frequency; and

a means for transmitting said output to the radar sensor to be used in testing the radar sensor, said rendering means being connected between said dimension-simulating means and said transmitting means.

2. A system for generating simulated radar targets of pre-selected dimensions at pre-selected simulated distances for testing a radar sensor as set forth in claim 1, wherein said intermediate frequency signal is Input radiation-32 GHz.

3. A system for generating simulated radar targets as set forth in claim 2, wherein said means for producing intermediate frequency signal comprises a first mixer coupled between said input radiation source and said distance-simulating means;

an oscillator for generating a predetermined frequency signal, said first mixer receiving and mixing said pre-determined frequency signal with said input radiation to produce said intermediate frequency signal prior to sending said intermediate frequency signal to said distance-simulating means.

4. A system for generating simulated radar targets as set forth in claim 3, wherein said distance-simulating means comprises a radio frequency-to-light-to-radio frequency converter positioned to receive said intermediate frequency signal from said first mixer and convert said signal to light;

and an optical fiber of pre-chosen length, both ends of said fiber being connected to said converter such that said light departs said converter and enters said fiber at one end, travels the length of said fiber, thereby achieving simulated distance, and re-enters said converter through the other end of said fiber, said converter re-converting said light to intermediate frequency signal.

5. A radar target simulator as set forth in claim 4, wherein said means for rendering said intermediate frequency into an output in the radar sensor'"'"'s operational frequency comprises a second mixer for mixing input signals;

a hybrid coupler coupled simultaneously between said first and second mixers and said oscillator, said coupler splitting said pre-determined frequency signal generated by said oscillator into two portions and forwarding one portion to said first mixer while forwarding the other portion to said second mixer;

an orthomode transducer;

a waveguide tee coupled to said second mixer to receive signals therefrom, said waveguide tee separating any received signal into a first part and a second part, said waveguide tee being further coupled to said orthomode transducer via a first path and a second path, said paths being of unequal lengths and said waveguide tee transmitting to said orthomode transducer said first part via said first path and said second part via said second path, said orthomode transducer producing, in response, an output signal having linear vertical polarization and linear horizontal polarization; and

a polarizer coupled to receive said linearly polarized output signal from said orthomode transducer and yield a final output signal having simultaneous left-hand and right-hand circular polarizations, said final output signal being in the radar sensor'"'"'s operational frequency range.

6. A radar target generating system as set forth in claim 5, wherein said dimension-simulating means comprises a power divider coupled to receive said intermediate frequency signal from said converter;

a power combiner coupled to said second mixer; and

a plurality of coaxial cables, said coaxial cables extending between said power divider and said power combiner and time-spreading by varying degrees said intermediate frequency signal in its travel from said power divider to said power combiner.

7. A radar target generating system as set forth in claim 6, wherein said plurality of coaxial cables is three in number.

8. A radar target generator as set forth in claim 7, wherein said transmitting means comprises a circular horn for transmitting said final output signal from said polarizer to the radar sensor.

9. A radar target generating system as set forth in claim 8, wherein said target generating system further comprises an attenuator coupled between said converter and said power divider, said attenuator imparting a pre-determined power level to said intermediate frequency signal.

10. A radar target generator as set forth in claim 9, wherein said target generator still further comprises a linear horn positioned between said input radiation source and said first mixer, said linear horn transmitting said input radiation as input frequency signal toward said first mixer.

11. A radar target generator as set forth in claim 10, wherein said target generator yet further comprises a means for supplying DC power to said oscillator.

12. A radar target generator for simulating targets of pre-selected dimensions at pre-selected distances for testing a radar sensor, the radar sensor having an operational frequency range, said target generator comprising:

a source of input radiation in the radar sensor'"'"'s operational frequency range;

a means for converting said input radiation to input frequency signal;

a first mixer for receiving said input frequency signal and a pre-determined frequency signal and producing intermediate frequency signal therefrom;

a radio frequency-to-light-to-radio frequency converter coupled to receive said intermediate frequency signal and convert said intermediate frequency signal to light;

an optical fiber of pre-chosen length, said fiber being positioned to provide a path for light from said converter to travel prior to returning to said converter, thereby simulating said pre-selected distance, said converter re-converting said returned light to said intermediate frequency signal;

a power divider and a power combiner with several coaxial cables connected therebetween, said cables imparting differentiated delay effects to said intermediate frequency signal, thereby simulating said pre-selected dimensions;

a means for rendering said intermediate frequency into an output in the radar sensor'"'"'s operational frequency; and

a means for transmitting said output to the radar sensor to be used in testing the radar sensor, said rendering means being connected between said dimension-simulating means and said transmitting means.

13. A radar target generator for simulating targets of pre-selected dimensions at pre-selected distances for testing a radar sensor as described in claim 12, wherein said means for rendering said intermediate frequency into an output in the radar sensor'"'"'s operational frequency comprises an oscillator for producing an input signal of a pre-determined frequency;

a second mixer for mixing input signals;

a hybrid coupler coupled simultaneously between said first and second mixers and said oscillator, said coupler splitting said pre-determined frequency signal generated by said oscillator into two portions and forwarding one portion to said first mixer while forwarding the other portion to said second mixer;

an orthomode transducer for producing an output signal having linear vertical polarization and linear horizontal polarization;

a waveguide tee for separating any incident signal into a first part and a second part, said waveguide tee being coupled to said orthomode transducer via a first path and a second path, said paths being of unequal lengths, said waveguide tee transmitting to said orthomode transducer said first part via said first path and said second part via said second path; and

a polarizer coupled to receive said linearly polarized output signal from said orthomode transducer and yield a final output signal having simultaneous left-hand and right-hand circular polarizations, said final output signal being in the radar sensor'"'"'s operational frequency range.

14. A radar target generator as described in claim 13, wherein said generator farther comprises at least one dB isolator coupled between said second mixer and said waveguide tee, said isolator shielding said generator from effects of any random external signals.

15. A radar target generator as described in claim 14, wherein said generator still further comprises a DC source;

and a voltage regulator, said regulator being coupled between said DC source and said oscillator.

16. A radar target generator as described in claim 15, wherein said generator yet farther comprises an attenuator coupled between said converter and said power divider, said attenuator receiving said intermediate frequency signal from said converter and imparting a desired power level to said intermediate frequency signal prior to forwarding said intermediate frequency signal to said power divider.