Compact ultra-wideband planar filter with RF-MEMS-based tunable notched band

This paper presents the design of a compact ultra-wideband (UWB) bandpass planar filter with a tunable notched band within the bandwidth. The filter can be used for wireless communications within the unlicensed UWB range (3.1-10.6 GHz). The UWB filter is based on external interdigitated quarter-wavelength microstrip resonators and a central half-wave microstrip resonator embedding a reconfigurable open-circuited stub. The stub introduces a narrow rejection band inside the UWB filter bandwidth. The frequency tuning of the notched band is obtained by sequentially activating three RF MEMS ohmic switches placed in series along the embedded stub. HFSS^® simulations of a 5^th order UWB filter show very low return (>;13dB) and insertion losses (<;0.3dB) in all stub states and good selectivity performance of the notched bands (up to -18dB of rejection). The device has been fabricating at FBK on quartz substrate; experimental results will be available soon.