Miniaturized Bandpass Filter Based on IPD-GaAs Technology with Mushroom-Substrate Integrated Waveguide Structure

This paper introduces a millimeter-wave miniaturized filter using GaAs-Ipd(Integrated Passive Device) technology, applied in the 5G N258 band (24.25-27.5GHz). The filter integrates mushroom structures within the Substrate Integrated Waveguide (SIW). The introduction of mushroom structures into the SIW introduces resonant modes independent of the SIW, enabling effective tuning of resonant frequencies by adjusting the upper and lower dielectric thickness ratio, thereby reducing the filter size. In the SIW, coupling exists between the mushroom structures, allowing multiple mushroom structures to be reasonably loaded into the SIW cavity to achieve a single-cavity multi-mode effect. In this work, a filter with a Cascaded Triplet (CT) structure is designed by integrating three mushroom structures into a single SIW cavity. Simulation results demonstrate that the filter, with a size of 1.3×1.3mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, achieves an insertion loss (IL) of 1.4 dB at the center frequency. The out-of-band rejection exceeds 20 dB in the ranges of 14-21.6 GHz and 29.2-40 GHz, with a transmission zero at 30.44 GHz. The performance of the designed filter closely matches the synthesized results.