Abstract: The present invention relates to an electronic identification system comprising one or more transponders which store identification and other information in memory, and readers, which capture information from the transponders and write new information thereto, and in which communications between transponders and readers are accomplished using radio frequency signals. The present invention has attributes which make it particularly useful in automatic fare collection systems, where transponders, typically in the form of thin cards and used as pre-paid tickets, are carried by fare paying passengers to replace printed tickets and eliminate exchange of cash. Specifically the system achieves simultaneous identification of numerous transponders by one reader, permits a reader to selectively program any of many transponders under its control, exhibits fast transaction speed to maximize passenger throughput, and achieves exceptional data storage integrity.

Abstract: A microwave detector, which integrates two circular patch antennas with a detector diode. The high impedance at the edge of the circular patch antenna is combined with 180.degree. out of phase electric fields at diametrically opposite points, so as to match to the RF impedance of a zero or small DC bias diode. The result is a very simple, high-sensitivity narrow-band microwave integrated detector.