A Compact L-Band Reconfigurable Dual-Mode Patch Filter

This research presents a novel dual-mode filter design that offers significant advantages in terms of frequency agility and miniaturization compared to conventional fixed multi-resonator filters. The design and implementation of a compact tunable bandpass filter are presented. The basic design structure is based on a slotted non-degenerate dual-mode microstrip square patch. The slots are etched symmetrically, which makes the slotted dual-mode square patch equivalent to a two-coupled-resonator filter. The asymmetrical feed lines enable the excitation of dual resonant modes. The patch length, slot size, and dielectric material properties primarily determine the filter's center frequency and bandwidth. Tunability is achieved by loading the slotted square patch with reversed bias varactor diodes located at the square patch corners, allowing electronic control of the filter center frequency. The design utilizes RT/Duroid 6010.2 laminates with a dielectric constant of 10.2 and a thickness of 0.635 mm. A bias tee at one of the filter ports is used to provide reverse bias to varactor diodes. Simulations and experimental results demonstrate tunable characteristics. Among the attractive features of the proposed design, good levels of insertion loss and impedance matching are noticed in the entire tunable band. The advantages of the proposed design make it well-suited for modern wireless technology applications in communication, radar, and satellite systems.