Interrogator/receiver system for use with a remote transponder

Interrogator/receiver apparatus for transmitting a first signal to, and receiving a second signal from a remote transponder of the type having (1) a plurality of signal conditioning means, coupled to receive said first signal, each signal conditioning means providing an intermediate signal having a known delay and a known amplitude modification to said first signal, and (2) signal combining means coupled to all of said signal conditioning means, for combining said intermediate signals to produce said second signal, said signal conditioning means and signal combining means imparting a known informational code to said second signal, said interrogator/receiver apparatus comprising:

• (a) common means for generating said first signal, said first signal being of radio frequency (RF);
• and
• (b) at least one transmitter/receiver means, remote from and coupled to said common signal generating means by means of an RF transmission line, for transmitting said first signal to, and receiving said second signal from a transponder, said transmitter/receiver means including:
• (1) a common transmit/receive antenna;
• (2) a signal mixer having two inputs and an output, one of said inputs being coupled to said transmission line;
• and
• (3) coupler means connected to said antenna, to said mixer and to said transmission line for preferentially passing said first signal from said transmission line to said antenna and preferentially passing said second signal from said antenna to said mixer,
• wherein said mixer causes four quadrant multiplication of said first signal by said second signal to produce a third signal containing frequencies equal to the instantaneous difference between the frequencies of said first and said second signals.