Compact inverted E-shaped open-circuited impedance matching stub bandpass filter for wireless applications

Abstract

The front and back ends of antennas in wireless communication systems primarily depend on filter design. This experimental study designed a compact inverted E-shaped open-circuited impedance matching stub with a uniform stepped impedance resonator (SIR) bandpass filter for the ultra-wideband (UWB) range of frequencies used in 4G and mid-band 5G wireless applications. The main challenge is to reject the spurious response of upper and lower stopbands with the help of uniform SIR BPF. The proposed filter design generates excellent selectivity and effective stopband rejection at both passbands ends using the symmetrical structure of SIR and inter-digital coupled feed lines. By modifying and positioning two open-circuited stubs on every side of the stub resonators for impedance matching, a bandpass filter (BPF) was made to attain a broad bandwidth and a high degree of selectivity. This study also investigated on various dielectric constant FR-4, Rogers RO-3003, Rogers RO-4003C, and RT/Duriod-6010 for the achievement of filter performances (4.6–7.3), (5.34–8.68), (5–8), (3–5) GHz respectively with the same design structure. Among these dielectric constants, the filter on RT/Duroid-6010 has good FBW (51.6%) and return loss (50 dB). For cost-effectiveness, the filter on the FR-4 substrate was fabricated and measured using a network analyzer, and the simulation results were as expected. Electromagnetic (EM) and Tubular schematic Circuit models were simulated using an Advanced Design System (ADS) tool. This filter exhibits a compact, efficient, wide passband with high selectivity and stopband rejection at both passband ends.