Compact Tunable Bandpass Filter with Continuous Control of Center Frequency and Bandwidth Independently

This paper presents a compact electrically tunable bandpass filter with continuous control of center frequency and bandwidth independently. The filter consists of two coaxial dielectric resonators loaded with two varactors for center frequency tuning. A symmetrical Y-type capacitor network used for tuning bandwidth is proposed. A prototype made of dielectric ceramics with dielectric constant of 88 has been designed, fabricated, and measured. The center frequency varies from 0.562 GHz to 0.845 GHz, and 3 dB bandwidth is tuned from 117 MHz to 194 MHz at the center frequency of 845 MHz. A constant absolute bandwidth of 141 MHz is realized by varying simultaneously bias voltages. The volume of fabricated filter containing bias networks is 24 x 22 x 6.5 mm3 (0.045 lambda 0 x 0.041 lambda 0 x 0.012 lambda 0). The measured results agree with the simulation outcome.