SAW antenna duplexer having a phase shifter with less than 50 ohm characteristic impedance

An antenna duplexer comprising:

• a transmitter surface acoustic wave (SAW) filter having an output port;
• a phase shift circuit having a first port and a second port, said first port being electrically connected with said output port of said transmitter SAW filter;
• and
• a receiver SAW filter having an input port that is electrically connected with said second port of said phase shift circuit,
• wherein said transmitter and said receiver SAW filters have different frequency bands, providing attenuation with each other,
• wherein said phase shift circuit is operable to shift a phase of said receiver SAW filter in its transmitter-band and has a phase angle and a characteristic impedance with which a magnitude of a reflection coefficient at a center frequency in the transmitter-band of said receiver SAW filter is to be not less than 0.8 and the phase angle of reflection coefficient at a center frequency in the transmitter-band of said receiver SAW filter is to be from 0° to 45°, and
• wherein the characteristic impedance of said phase shift circuit is 42±8 ohms excluding 50 ohms, and the phase angle of said phase shift circuit is 90±10°.

An antenna duplexer comprising:

• a transmitter surface acoustic wave (SAW) filter having an output port;
• a phase shift circuit having a first port and a second port, said first port being electrically connected with said output port of said transmitter SAW filter;
• and
• a receiver SAW filter having an input port that is electrically connected with said second port of said phase shift circuit,
• wherein said transmitter and said receiver SAW filters have different pass bands and attenuate the other pass band with each other, and
• wherein said phase shift circuit is operable to shift a phase of said receiver SAW filter in its transmitter-band and has a less-than-50 ohm characteristic impedance.