Briefly, in accordance with one embodiment of the invention, a combiner may include transmission lines to couple a receive port and a transmit port to an antenna at a common junction. Shunt admittance elements may be utilized at the transmit and the receive ports to isolate one of the transmit and the receive ports from the antenna by shunting the at least one of the transmit and the receive ports to a power supply potential such as a ground reference. During a transmit mode, the shunt admittance element at the receive port may shunt the receive port to the power supply potential, thereby isolating the receive port from the antenna. During a receive mode the shunt admittance element at the transmit port may shunt the transmit port to the power supply potential, thereby isolating the transmit port from the antenna.
The present application is a continuation of U.S. patent application Ser. No. 10/330,386 filed Dec. 26, 2002, entitled "TRANSMIT/RECEIVE COMBINER USING SHUNT ADMITTANCE ELEMENTS FOR ISOLATION", which is incorporated herein by reference.
A circuit for combining/splitting first and second RF signals having different wavelengths of x and y, respectively, the circuit comprising: (a) first and second transmission portions coupled at an intersection, the first transmission portion comprising at least two intersecting transmission lines, each having a length which is an odd multiple of about 1/4 y, the second transmission portion comprising at least two intersecting transmission lines, each having a length which is an odd multiple of about 1/4 x; and (b) first, second and third ports, the first port located at the first transmission portion, the second port located at the intersection of the first and second transmission portions, and the third port being located at the second transmission portion, the first and second ports being electrically coupled, and the second and third ports being electrically coupled.
