Compact Filtering Switch With Harmonic Suppression Based on Coupling Control

In this paper, a compact filtering switch with harmonic suppression based on coupling control is presented. The ON- and OFF-states are enabled by turning on and off the PIN diodes in the feeding lines of a bandpass filter (BPF). In the ON-state, the PIN diodes are turned off, which do not cost extra loss. The whole circuit is the same as a conventional BPF. Meanwhile, a coupling structure between resonators is utilized to suppress the second harmonic, resulting in wide stopband. In the OFF-state, discriminating coupling is introduced, where the coupling coefficient between the feeding line and resonator is controlled as zero. Thus, high isolation is obtained. For demonstration, the filtering switch is implemented. The measured results show that the proposed filtering switch exhibits low ON-state loss, wide stopband performance and high OFF-state isolation.