Design of a compact dual-band-notch ultra-wideband bandpass filter based on wave cancellation method

In this study, a compact ultra-wideband (UWB) bandpass filter (BPF) with sharp roll-off, improved out-of-band performance and dual-band-notch operation is presented and its design procedure is discussed. In the proposed structure, in order to reject the unwanted harmonic pass bands, a pair of modified cross-shaped coupled lines (CCLs) is implemented along the ports of the filter. Moreover, a pair of half-circle-shaped stubs and a stepped-impedance stub are loaded on the main resonator in order to obtain additional transmission zeros (TZs) which are controllable separately. Implementation of the CCLs and the stub loaded resonator (SLR) reduce the total size of the presented microstrip BPF. Besides, by extending and folding the upper coupled line of each CCLs and also through an open stub which is protruded inside a slot on the main resonator, dual-band-notch operation is added to the performance of the presented filter. The fabricated prototype has a small size and is capable to cover frequency band of 2.8–10.69 GHz with two band-notch functions at 4.9–5.4 and 7.83–8.25 GHz which suppresses the interference between UWB spectrum with wireless local area network (WLAN) and satellite communication frequency bands, respectively. The proposed filter has a compact size while showing good return loss and insertion loss characteristic in the frequency band of interest.