Microstrip Multiplexer and Switchable Diplexer with Joint T-Shaped Resonators

This work presents a four-channel multiplexer that uses joint T-shaped resonators. The multiplexer contains four second-order bandpass filters that are combined by two joint T-shaped resonators. The joint T-shaped resonators are also inherently the resonant elements and frequency selective signal splitter. Therefore, the proposed multiplexer has compact size because of fewer resonators and no matching/combining circuit. The T-shaped resonator also makes the presented structure suitable for multiplexers having very close bands. The multiplexer is then modified to obtain a switchable FDD diplexer which is an important device in dual-band wireless communication system. The mechanism of band switching is discussed. Only two diodes are required to control the switching between the two FDD bands. Good agreement between the simulated and measured responses validates the proposed structure.