Dual Channel Diplexer based on Stepped Impedance Filter and Microstrip Open-Loop Resonator

This paper presents a dual-channel, wide-band diplexer design using coupled stepped impedance resonators (SIRs) for lower frequency (0-3.3 GHz) and open-loop resonators for upper-frequency channels (3.3-4.5 GHz). The impedance length ratio of SIRs is tuned to the desired resonant frequency. A cross-shaped open loop square ring resonator is used for the upper-frequency channel. The insertion losses in the pass bands are less than 3 dB. The two operating channels have measured better than 26 dB of isolation.