SAW antenna duplexer for trunking communication

The trunking communication system operating on 300-400 MHz requires an antenna duplexer with low insertion loss, sharp-cutoff frequency characteristics, reactive characteristic in the mutual frequency bands and small size, which is not commercially available. We have proposed a SAW antenna duplexer to fulfill the requirements mentioned above. To satisfy the demand of reactive characteristic in the mutual frequency bands to reduce disturbing between the Rx and the Tx, we add a π-type high pass LC filter between the antenna and the Rx as phase shifter. In order to both get good stopband rejection and enhance the power endurance, we divide the Tx filter into two parts, one part before the power amplifier and the other coupling with antenna. The part before the power amplifier is composed of a ladder-type SAW filter coupled with SAW bandstop filter with insertion loss about 2.1 dB and attenuation about 60 dB in receiving frequency band (382-386 MHz). The part coupling with the antenna is composed of a ladder-type SAW filter with insertion loss about 0.6 dB and attenuation about 15 dB in receiving frequency band. The Rx filter is composed of a ladder-type SAW filter coupled with a longitudinally coupled resonator filter in the receiver with insertion loss about 3.8 dB and high attenuation of about 60 dB in the transmitting frequency band (372-376 MHz).