1RU GSM duplexers with extracted poles

Two low cost full band GSM combline duplexers have been developed for 1RU 19" rack mounting. They achieve a typical insertion loss of <0.3 dB, with isolation of >40 dB and >50 dB respectively. The duplexer is implemented with round resonators in rectangular slabline with no internal walls to reduce costs. Coupling to the common and Tx/Rx ports is implemented with interdigitally oriented rod transformers, for best physical orientation and low intermodulation products. The Tx and Rx filters each use an extracted pole resonator (to achieve the isolation), which is easier to assemble and tune than the more usual cross-coupled resonator approach