0.7-1.0-GHz Switchable Dual-/Single-Band Tunable Bandpass Filter Using a Switchable J-Inverter

Cognitive radios require tunable band-switchable bandpass filters to respond to the dynamically changing operating frequencies in cognitive systems. This study presents a novel switchable dual-/single-band tunable bandpass filter using a single switchable J -inverter. The proposed filter configuration can be easily converted from a two-pole dual-passband mode to a four-pole single-passband mode using the single J-inverter with switches. This is achieved through a novel dual-band bandpass filter configuration using hybrid resonators that consist of two parallel resonators and one J-inverter. In addition, two bandwidths and two center frequencies of the dual-passband mode are designed, and a high stopband attenuation level is achieved due to a transmission zero between the two passbands. The proposed filter is built on a Duroid substrate with a dielectric constant of 3.48 and a thickness of 30 mil. The tuning of the center frequency and the passband number change are carried out using silicon varactors and PIN diodes. In the four-pole single-passband mode, a center frequency tuning of 0.75-1.08 GHz is achieved with 1-dB bandwidths of 105-158 MHz. The two-pole dual-band bandpass filter mode has a center frequency tuning of 0.69-0.9 GHz (low-band) and 0.85-1.07 GHz (high-band). It has potential for application in wideband cognitive radios.