Distance measuring equipment

• US 3,969,725 A
• Filed: 06/12/1974
• Issued: 07/13/1976
• Est. Priority Date: 06/12/1974
• Status: Expired due to Term

• 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 Agriculture
• Inventors: Couvillon, James Benedict, Maher, Robert Allen, Daniels, William Dorsey, Gassner, Ronald Lee
• Primary Examiner(s): Tubbesing, T.H.
• Application Number:
  US05/478,651
• Time in Patent Office: 762 Days
• Field of Search: 343/6.5 R, 343/17.2 PC
• US Class Current: 342/47
• CPC Class Codes: G01S 13/282 using a frequency modulated carrier wave G01S13/286 takes precedence
• CPC Class Codes: G01S 13/76 wherein pulse-type signals are transmitted

Abstract

Disclosed is improved distance measuring equipment comprising an airborne FM coded, chirp, interrogator transmitter in combination with a weighted matched receiver in a ground transponder. The airborne transmitter produces a long low power frequency modulated output pulse. Detection in the transponder receiver is accomplished by pulse compression matched filter techniques.

Claims

1. Distance measuring equipment for measuring the distance from an airborne interrogator to a ground based transponder comprising;

an interrogator encoder for providing a linear frequency modulated pulse modulated signal with selectable slope sign;

interrogator transmitter means for mixing a preselected radio frequency signal with the interrogator encoder pulse and transmitting the resulting radio frequency pulse;

transponder receiver means for receiving interrogator transmissions and providing an intermediate frequency output in response thereto;

a matched pulse compression filter coupled to the transponder receiver for providing time compression and signal to noise gain for intermediate frequency signals having a preselected center frequency and linear frequency modulated frequency modulation with separate detection for both modulation slope signs;

transponder decoder means coupled to the pulse compression filter for detecting the arrival of the leading edge of a received pulse and providing an output pulse indicating said arrival;

transponder transmitter means coupled to said transponder decoder means for transmitting a pulse of radio frequency signals at a preselected frequency in response to the decoder output;

interrogator receiver means for receiving transponder transmissions and providing an intermediate frequency output in response thereto;

interrogator decoder means coupled to the interrogator receiver for detecting the arrival of a transponder pulse having a preselected center frequency and providing an output indicating said arrival; and

range calculating means coupled to the interrogator encoder and the interrogator decoder for measuring the time between an interrogator transmission and reception of a transponder transmission and providing an output proportional to the distance from the interrogator to the transponder.

2. Distance measuring equipment according to claim 1 wherein the interrogator encoder comprises a local oscillator, a one-shot for providing a preselected width video pulse, a mixer coupled to the local oscillator and one shot for providing a pulse of intermediate frequency signal having the preselected width, and a surface wave device pulse expander coupled to the mixer for providing a time expanded frequency modulated output pulse.

3. Distance measuring equipment according to claim 1 wherein the pulse compression filter comprises a surface wave device.

4. Distance measuring equipment according to claim 1 wherein the transponder receiver means includes a limiter amplifier for limiting the amplitude of the intermediate frequency output to a single preselected level.

5. In distance measuring equipment for measuring the distance from an airborne interrogator transmitter to a ground based transponder receiver, the method of providing pulsed radio frequency interrogation signals comprising:

time expanding and linear frequency modulating said radio frequency pulses transmitted by said interrogator transmitter;

time compressing and frequency demodulating said radio frequency pulses received by said transponder; and

reversing said linear frequency modulation of said pulses on alternate interrogations in order to cancel transmission errors.