A split band duplexer for PCS CDMA mobile phones

State-of-the-art duplexers for mobile phones show significant variations of insertion loss within the transmitter (TX) and receiver (RX) frequency bands. The result is a high in-band loss due to the high attenuation requirements. This work presents a novel concept and experimental results about minimizing loss in the transmit path. Splitting the full transmit band into two half bands reduces the insertion loss significantly by using two optimized TX filters. Both TX paths are connected to the antenna by a low loss switch of the single pole double throw (SPDT) type. Circuit simulations have been performed and FR-4 evaluation boards for the PCS band (1900 MHz) have been built. The measurement results show an improvement of up to 1.7 dB in the TX path. Consequently, the presented concept reduces the power consumption and increases the talk-time of the mobile phone.