Compact bandpass filter with tunable center frequency and reconfigurable bandwidth

In this paper, compact filters with independent control of center frequency and bandwidth are proposed. Center frequency tuning is realized by changing the electric length of varactor diode loaded resonators, bandwidth reconfiguration is achieved through a convenient way to control the inter-resonator coupling by switching on/off narrow strips connecting two resonators at different positions while good matching for widely variable bandwidth status is enabled by tapped input combined with variable capacitance or variable inductance, i.e., variable admittance inverter to control external coupling. Quarter wavelength stepped impedance resonator allows for constant absolute bandwidth (ABW) tuning over large tuning ranges from 1.178 GHz to 3.6GHz (for the widest bandwidth only), widely variable bandwidth states from 140MHz to 1.4GHz is demonstrated.