volume | PIER Journals

Abstract

This study presents a compact and tunable microstrip of a dual-path wideband filter that employs coupled-lines and varactors to address the needs of 4G/sub-6 GHz 5G communication systems. This work integrates tunable methods inspired by wideband parallel coupled line-based topologies to realize a reconfigurable solution achieving a 34% frequency tuning range (1.13-1.51 GHz) while maintaining a low insertion loss of approximately below 1 dB. Specifically, the proposed microstrip-based filter, which is designed, uses parallel coupled-line resonators with a quarter-wavelength length, enabling a broad tuning range between 1.27 and 1.54 GHz. Adjusting the coupling strengths of both adjacent and non-adjacent resonators, the filter can be shifted within this frequency band without compromising performance. Therefore, to achieve the desired level of control, two identical varactor diodes and biasing circuitry are meticulously selected for their stable and repeatable capacitance-voltage characteristics to adjust the filter's resonant frequency. The optimal positions for these tuning circuits are determined based on the resulting capacitance, which is crucial for achieving a wide tuning range. Simulation and measurement confirm that this reconfigurable microstrip filter, implemented on a 60.7 x 35.4 mm² footprint, benefits not only from a reduced footprint but also from the ability to target multiple frequency bands with minimal hardware modifications, delivering the intended performance for modern wireless front ends.

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Dr. Siti Aminah Nordin

Dr. Muhammad Asraf Hairuddin

Dr. Zakiah Mohd Yusoff

Mr. Gaetan Prigent

Dr. Nur Dalila Khirul Ashar