A microstrip diplexer filter using stepped-impedance resonators

Parallel coupled-line filter covers odd and even wave coupling of transmission lines. Cascading parallel coupled-line sections gives rise to a bandpass filter structure. Since conventional parallel coupled-line filter has poor spurious response and isolation performance, step impedance technique is added to improve its performance. A new Zig-Zag diplexer filter using stepped-impedance resonators is proposed in this paper. This diplexer filter has a narrow-band bandwidth, high isolation between its terminals, and operates at 2.4 GHz and 5 GHz, which are the frequencies for Wireless LAN applications. The simulation results show that this microstrip filter has excellent performance on return loss, insertion loss, and isolation.