RESEARCH ARTICLE A multi-stub loaded compact UWB BPF with a broad notch band and extended stopband characteristics Puja Kumari 1 | Pankaj Sarkar 2 | Rowdra Ghatak 1 1 Microwave and Antenna Research Laboratory, ECE Dept., National Institute of Technology Durgapur, Durgapur, India 2 ECE Dept., School of Technology, North Eastern Hill University, Shillong, Meghalaya, India Correspondence Pankaj Sarkar, ECE Dept., School of Technology, North Eastern Hill University, Shillong 793022, Meghalaya, India. Email: pankajsarkar111@gmail.com Abstract A compact ultrawideband (UWB) bandpass filter (BPF) employing the principle of multiple mode resonance characteristics to create UWB passband with high selec- tivity and simultaneously having extensive stopband characteristic is presented. Utilizing five stubs attached along with the asymmetric trisection stepped imped- ance resonator (ATSSIR), the proposed resonator enables seven transmission poles inside the passband. As an additional attributes the projected filter triggers one transmission zero at 5.0 GHz which helps to mitigate WLAN signal interference. No additional circuitry is used to generate a notch band. The proposed prototype of UWB BPF is fabricated and estimated. Simulated and estimated results are in great understanding. The prospective filter displays a deliberate passband from 2.9 to 11.02 GHz. The filter unveils deceptive free wide upper stop band attributes till 25 GHz with least attenuation of 10 dB all through the stop band. KEYWORDS Asymmetric Tri-Step Stepped Impedance Resonator, Extended stopband, Multiple Mode Resonance, Notch band, Ultra wideband 1 | INTRODUCTION Ultra wideband (UWB) communication system frame- work has evolved with a vast transmission data transfer capacity utilizing a band covering 3.1 to 10.6 GHz. 1-3 Frontend circuits such as filters assume indispensable part in governing the overall performance. This necessitates higher efficacy of such filters with low passband insertion loss, better selectivity, higher stop band, and plane group- delay. Realization of circuits in planar domain to achieve a wide passband puts forward stringent design con- straints. A farrago of methods has been adopted over the years to design bandpass filters (BPF) to cover this wide- band. Combination of highpass filters and lowpass filters, 4 coupling of multimode resonators (MMRs) 5,6 are some of the techniques adopted in this regard. In certain cases, 6-8 multimode resonators have been coupled to either cancel or add the desired modes resulting in band notched UWB BPFs. Several UWB BPFs using stub loaded multimode reso- nators are reported in References 9-12. In Reference 9, few stubs are loaded with a ring resonator to implement UWB BPF. Even and odd mode method is used to ana- lyze the resonant characteristics of the proposed resona- tor. To make the coupling stronger aperture backed parallel-coupled lines are used. Parallel-coupled lines are used to design UWB BPF which is reported in Reference 10. The proposed structure comprises of two parallel- coupled lines, one is open circuited and the other one is short-circuited. One transverse transmission line is used which creates transmission zeros at lower and upper cut- off frequencies to improves the selectivity. A multiple- mode resonator based UWB BPF is designed in Reference 11 which includes a triangular ring loaded stub resonator (TRLSR) connected at the middle of SIR along with C- shaped and E-shaped resonator. Triple notch bands are constructed by using C- and E-shaped resonator. A stub- loaded multiple-mode resonator based UWB BPF is Received: 15 October 2019 Revised: 16 December 2019 Accepted: 21 December 2019 DOI: 10.1002/mmce.22138 Int J RF Microw Comput Aided Eng. 2020;e22138. wileyonlinelibrary.com/journal/mmce © 2020 Wiley Periodicals, Inc. 1 of 8 https://doi.org/10.1002/mmce.22138