Miniaturized UWB Bandpass Filters With Notch Using Slow-Wave CPW Multiple-Mode Resonators

In this letter, a miniaturized, ultra-wideband (UWB) filter with notch using a slow-wave co-planar waveguide (CPW) multiple-mode resonator (MMR) is presented. By employing a slow-wave CPW MMR, the resonator length is reduced by 40% at mid-band frequency compared to the conventional CPW MMR. The proposed UWB filter employs stub-loaded microstrip-CPW transitions that improve the rejection skirt and defected ground structures (DGS) to provide better stopband rejection. A novel bridge structure is proposed to create a notch in the filter passband to reject WLAN interference. A passband from 3.1 to 10.6 GHz (110% bandwidth around 6.85 GHz) with a rejection notch at 5.65 GHz is achieved with insertion loss of 0.9 dB and return loss better than 10 dB. Using DGS, a rejection greater than 22 dB is achieved from 11 to 16 GHz while still having a 25% reduction in filter size compared to the conventional case. Design, simulation and measurement of filter prototypes are presented.