Compact and High Isolation Microstrip Six-Channel Diplexer Using Multi-Mode Stepped-Impedance Resonators

A compact and high isolation microstrip six-channel diplexer has been proposed. The diplexer is formed by connecting two tri-band bandpass filters (BPFs) to a single feed with multiple coupling paths. By using the distributed coupling technique, the input matching circuit is not needed anymore, resulting in a smaller circuit size. In addition, by employing the multi-mode stepped-impedance resonators (SIRs), a diplexer with compact size and flexible frequency allocation can be implemented. For a demonstration, a six-channel diplexer with third-order Chybeshev bandpass response is designed and fabricated using microstrip technology. The size of the fabricated diplexer is only about 0.69 λ
_g
× 0.21 λ
_g
. Moreover, the isolation between the output channels is larger than 35 dB.