A Switched Reconfigurable High-Isolation Dual-Band Bandpass Filter

This letter presents an independently switched, reconfigurable, dual-band filter of high isolation between two closely-positioned adjacent bands. The reconfigurable fourth-order bandpass filter (BPF) prototype consists of two individual filters and a double-diplexing configuration, which enables independent synthesis of BPF on each band. This letter reports the diode-loaded resonator approach to the dual-band BPF design, achieving independent switching control of band selection without affecting the original bandpass characteristics. Measured results are in close agreement with the simulations and validate the design methodology presented in the letter, showing two mid-band frequencies f(A) and f(B) at 1.5 and 2 GHz, of fractional bandwidths 11.4% and 10.8%, respectively. The measured worst-case passband insertion loss is less than 3.1 dB, while achieving band isolation higher than 37 dB.