This invention relates generally to signal interfaces, such as antenna signal interfaces, that perform both transmit and receive functions.  An antenna is a conductive structure that can carry an electrical current.  Antennas can be used to transmit and receive electromagnetic waves.  If a time varying electrical current is electrically coupled to an antenna, the antenna will radiate an electromagnetic wave.  If a time-varying electromagnetic field is received by an antenna, the antenna will generate a time varying electrical current. 
Signal interfaces are used to efficiently transfer power.  For example, an antenna signal interface is used to efficiently transfer power between an antenna and transmit and/or receive electronics.  A transmitter antenna interface is designed to transfer power efficiently from a transmission line that electrically couples a transmitter to the antenna.  A receiver antenna interface is designed to transfer power efficiently from the antenna to a transmission line that is electrically coupled to a receiver.  A transceiver antenna interface is a bi-directional interface that is designed to transfer power efficiently from a transmission line that is electrically coupled to a transmitter to the antenna and also is designed to transfer power efficiently from the antenna to a transmission line that is electrically coupled to a receiver.