Design of Low-Loss Single-Pole Single-Throw and Single-Pole Double-Throw Filtering Switches Using Coaxial Resonators

In this paper, a single-pole single-throw (SPST) filtering switch and a single-pole double-throw (SPDT) filtering switch are designed using coaxial resonators. The ON- and OFF-states are achieved by controlling the PIN diodes embedded in the coaxial filter structures. For the SPST filtering switch, four PIN diodes are all turned off to achieve the ON-state, functioning as same as a conventional four-order coaxial filter, where the cross-coupling is employed to realize high-selectivity filtering responses. When the four PIN diodes are turned on, the SPDT switch works in the OFF-state. Capacitors are connected to the coaxial resonators to change the resonant frequencies of the resonators, thus the passband cannot be formed, resulting in a high isolation between the two ports. For demonstration, a SPST filtering switch is fabricated. Measured results show a low insertion loss of less than 1 dB and a high isolation of better than 60 dB. The excellent performance makes it attractive in wireless systems. Moreover, a SPDT filtering switch is also proposed. Compared with the state-of-the-art works using DR-based resonators, the proposed design shows a more compact size.