Transponder-responder system

Abstract

A transponder-responder system is provided which comprises a home station and at least one remote station. A transmitter at the home station periodically generates interrogation pulses by means of a directional sweep antenna across a search area. Each remote station includes a receiver and transmitter. Upon receipt of an interrogation pulse by the remote station receiver and while enabled, the remote station transmitter transmits a digitally encoded response signal which is received by a receiver at the home station. Upon receipt of the response signal by the home station receiver, timing circuitry at the home station determines the distance between the home and remote station by measuring the elapsed time between the transmission of the last interrogation pulse and the receipt of the response signal. Additionally, the home station includes circuitry which determines the rotational position of the sweep antenna and circuitry which decodes the response signal.

I claim: 
     
       1. A transponder-responder system comprising a home station and at least one remote station, said home station having means for transmitting a periodic interrogation pulse via a directional antenna and means for varying the rotational position of said antenna, said remote station comprising means for receiving said interrogation pulse, means for transmitting an encoded signal is response to the receipt of said interrogation pulse, and means for varying the encoding of said encoded signal, and   said home station further comprising means for receiving said encoded signal, means for decoding said encoded signal, means for determining the elapsed time between the transmission of the last interrogation pulse and the receipt of said encoded signal, means for determining the rotational position of the directional antenna and means for storing two encoded signals from two remote stations, said storing means further comprising a receiving register for storing the rotational position of said antenna, the decoded signal and said elapsed time upon the receipt of said encoded signal, the output of each receiving register being connected to the input of a holding register, the output from each holding register being connected to the input of a display register and means for displaying the contents of each display register, and upon receipt of two successive encoded signals by the home station, means for automatically loading the display registers with information pertinent to the first received encoded signal and for automatically loading the holding registers with information pertinent to the second received encoded signal.   
     
     
       2. The invention as defined in claim 1 and including manually operated means for loading said display registers with the contents of said holding registers. 
     
     
       3. The invention as defined in claim 1 wherein said remote station includes means for indicating the transmission of said encoded signal from said remote station. 
     
     
       4. The invention as defined in claim 1 wherein said means for varying the encoding of the encoded signal at the remote station comprises a multibit parallel-to-serial shift register having a clock input and a data input for each bit position, switch means for presetting at least two data inputs, and oscillator means operating at a predetermined frequency coupled to the input of said shift register, wherein the serial output from said shift register is operatively coupled to a transmitter at the remote station. 
     
     
       5. The invention as defined in claim 4 wherein said decoding means comprises a multibit serial-to-parallel shift register having a serial data input and a clock input, a second oscillator operating at said predetermined frequency coupled to the clock input of said serial-to-parallel shift register, and the output from said home station receiving means being coupled to the serial input of said last-mentioned shift register, whereby the parallel-to-serial shift register at the remote station is synchronized in operation with the serial-to-parallel shift register at the home station. 
     
     
       6. The invention as defined in claim 1 wherein said remote station receiving means and said home station transmitting means are tuned to a first frequency and wherein said remote station transmitting means and said home station receiving means are tuned to a second frequency. 
     
     
       7. The invention as defined in claim 1 wherein said means for determining the rotational position of said antenna comprises an Azimuth wheel coupled to said antenna so that said wheel rotates in unison with said antenna, said wheel having markings formed at predetermined intervals around its periphery, stationary pickup means for detecting said markings on said wheel and generating an output signal in response thereto, and counting means having an input connected to the output from said pickup means whereby the count in said counter is representative of the rotational position of said Azimuth wheel. .Iadd. 8. A transponder-responder system comprising a home station and at least one remote stations, said home station having means for transmitting a periodic interrogation pulse via a directional antenna and means for varying the rotational position of said antenna; said remote station comprising means for receiving said interrogation pulse, means for activating a first predetermined frequency oscillator contained in said remote station upon receipt of said interrogation pulse, said means for activating said first oscillator comprising a single shot multivibrator comprising a multivibrator responsive to the receipt of said interrogation pulse for generating an output pulse of a predetermined duration, said multivibrator output pulse being connected as an input signal to said first oscillator, said oscillator being activated only during the duration of said multivibrator output pulse, and means responsive to the output from said first oscillator for transmitting a serially encoded signal at a frequency correlated to the frequency of said first oscillator, wherein the duration of transmission of said encoded signal is substantially the same as the duration of said multivibrator output pulse;   said home station further comprising means for receiving said encoded signal, a second oscillator contained within the home station and having a frequency substantially the same as said first oscillator, means for activating the second oscillator upon receipt of said encoded signal, a deserializer having a data input and/or clock input, the output from said home station receiving means being connected to said deserializer data input and the output from said second oscillator being connected to said deserializer clock input, means for determining the elapsed time between the transmission of the last interrogation pulse and the receipt of said encoded signal, means for determining the rotational position of the directional antenna, means for storing the value of said elapsed time, the rotational position of the directional antenna and the output from the deserializer upon receipt of said encoded signal. .Iaddend. .Iadd. 9. The invention as defined in claim 8 wherein said means for determining the elapsed time further comprises a free running oscillator, having an output connected to a counter, means for resetting said counter a predetermined period following the transmission of said interrogation pulse to thereby compensate for internal delays in said home and remote stations. .Iaddend..Iadd. 10. The invention as defined in claim 8 wherein said remote station includes means for varying the encoding of said encoded signal. .Iaddend..Iadd. 11. The invention as defined in claim 10 wherein said serially encoded signal comprises a plurality of binary level bits, the first and last bit of said signal being encoded at a predetermined level, said deserializer having outputs corresponding to said first and last binary level bits, connected to said deserializer means for detecting said first and last bits at said predetermined level and for generating a strobe signal in response thereto, said strobe signal being connected to and activating said storing means. .Iaddend..Iadd. 12. The invention as defined in claim 11 wherein said means for detecting the level of said first and last bits of the encoded signal comprises an AND gate having its inputs connected to the first and last bit outputs of the deserializer. .Iaddend..Iadd. 13. The invention as defined in claim 11 wherein said storing means comprises a plurality of registers each having data inputs and a clock input which loads the signals on the data inputs into each respective register, said strobe being connected to said clock inputs of said registers. .Iaddend. .Iadd. 14. The invention as defined in claim 1 wherein said deserializer is a serial to parallel shift register. .Iaddend..Iadd. 15. The invention as defined in claim 8 wherein said remote station receiving means and said home station transmitting means are tuned to a first frequency and wherein said remote station transmitting means and said home station receiving means are tuned to a second frequency. .Iaddend..Iadd. 16. The invention as defined in claim 8 wherein said means for determing the rotational position of said antenna comprises an Azimuth wheel coupled to said antenna so that said wheel rotates in unison with said antenna, said wheel having markings formed at predetermined intervals around its periphery, stationary pickup means for detecting said markings on said wheel and generating an output signal in response thereto, and counting means having an input connected to the output from said pickup means whereby the count in said counter is representative of the rotational position of said Azimuth wheel. .Iaddend.