| 摘要 |
In a first aspect, the present invention relates to a transponder (TR) comprising: (i) a receiver and associated receiving antenna (A<SUB>TR</SUB>) for receiving incoming radar pulses in a first frequency band (F<SUB>1</SUB>) at an unknown pulse repetition rate, (ii) means for calculating the pulse repetition rate, (iii) a frequency synthesiser for generating a signal in a second frequency band (F<SUB>2</SUB>), (iv) modulation means for modulating the signal generated by the frequency synthesiser so as to encode information into the signal, and (v) a transmitter and associated transmitting antenna (A<SUB>TT</SUB>) for transmitting said modulated signal, wherein the transmitted signal is synchronised with the calculated pulse repetition rate of the incoming radar pulses and modulation of the transmitted signal is such that accurate positioning of the transponder (TR) can be determined at a remote receiver (RE). The invention also relates to a transponder receiver comprising: (i) a receiving antenna (A<SUB>RE</SUB>) for receiving modulated signals transmitted from a transponder (TR) in accordance with the first aspect, (ii) signal processing means for extracting data and positioning information from said signals and (iii) information output means.
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