A Controllable Bandwidth Filter Using Varactor-Loaded Metamaterial-Inspired Transmission Lines

This letter presents a tunable bandwidth bandpass filter based on varactor-loaded metamaterial coplanar waveguide (CPW) lines. The CPW lines are based on series gaps and split-ring resonators. The varactors are reverse-biased semiconductor diodes connected between both sides of each series gap. This configuration, directly inspired from the so-called metamaterial technology, takes advantage of the high dispersion of the loaded transmission line. Therefore, strong permittivity and permeability responses induced by means of the resonators are obtained. A single varactor-loaded transmission line is first analyzed. Then, a third-order tunable filter with fractional bandwidth tuning range from 5.8% to 21.5% is experimentally assessed. The proposed filters can be used in several practical applications such as multichannel wireless and satellite communication systems, where reconfigurable devices are often required.