0.7–1.0-GHz Reconfigurable Bandpass-to-Bandstop Filter With Selectable 2- and 4-Pole Responses

A 0.7-1.0-GHz reconfigurable bandpass-to-bandstop filter with selectable 2- and 4-pole responses is presented. The proposed filter can act as a 2- or 4-pole bandpass or bandstop filter by changing the coupling paths using zero-value coupling coefficients. The 4-pole bandpass filter mode also includes bandwidth control. The filter is built on a Duroid substrate with ε r=10.2 and h=25 mil. The center frequency tuning, as well as the bandpass-to-bandstop transformation and the selection of the number of poles are achieved using silicon varactor diodes and RF microelectromechanical systems switches. In the 2- and 4-pole bandpass modes, an insertion loss of 4.9-2.9 and 6.1-4.8 dB is measured at 0.71-0.99 and 0.72-1.01 GHz, respectively. The 4-pole bandpass mode also shows a bandwidth tuning of 28-85 MHz at 0.9 GHz. In the 2- and 4-pole bandstop modes, rejection levels of 24-28 and 32-41 dB are measured at 0.64-0.96 and 0.71-0.96 GHz, respectively. The application areas are in reconfigurable filters for wideband radios under high interference environments.