A compact and high isolation microstrip switchable diplexer

A compact, high-selectivity, and high-isolation microstrip electronically switchable diplexer is proposed. The diplexer is formed by connecting two switchable dual-band filters to a single feed with multiple coupling paths. No extra matching network is required for this design, which results in a smaller circuit size. In addition, the p-i-n diodes are loaded at one end of the assembled resonators to allow the proposed diplexer to be switchable. For the demonstration, a third-order bandpass switchable diplexer with four operating states is designed and fabricated using microstrip technology. Each channel band can be switched on and off independently. The diplexer has a compact size of 0.27 by 0.16 Excellent isolation between channels of better than 55 dB is also achieved.