Voltage-controlled filtering attenuator with fully tunable passband and attenuation

A voltage-controlled filtering attenuator (VCFA) with tunable central frequency, bandwidth, and attenuation of the passband is proposed. Four individual tunable poles in the passband are generated by a novel tunable quadruple mode resonator (TQMR) loaded with varactor diodes, and multiple zeros adjacent to the passband are introduced by internal grounded stubs and coupled line structure, which can significantly suppress spurious passband. The four passband poles and the external quality factor (Q_e) of the TQMR can be co-tuned by only four varactor diodes, achieving fully tunable capability of the central frequency and bandwidth for a single passband. The two open ends of the TQMR can be loaded with high impedance PIN diodes, which affect the tunable resonant modes slightly, therefore, a directionally coupled feeding network with tunable attenuation is integrated designed with the TQMR. Measurement results demonstrate an 18-dB tunable attenuation range, with the center frequency (f₀) continuously adjustable from 0.94 to 1.3 GHz at a fixed bandwidth of 180 MHz, while the bandwidth can be tuned from 150 to 480 MHz when maintaining a typical f₀ of 1.12 GHz.