A 10.3–14 GHz Glass-IPD Bandpass Filter Using Mutually Coupled Inductor Resonators

Glass-substrate integrated passive device (IPD) technology is attractive for heterogeneous radio frequency (RF) integration, but realizing high-selectivity bandpass filters (BPFs) with wide stopbands within a constrained footprint remains challenging. This paper presents a 10.3–14 GHz BPF that addresses limitations by introducing a novel mutually coupled inductor–resonator topology. Rather than relying on extra physical components, this architecture absorbs the function of the conventional inter-stage inductor into the magnetic coupling between two shunt resonators, reducing parasitic effects associated with inter-stage connections. An even- and odd-mode analysis is established to map the conventional lumped prototype to the proposed coupled network, thereby enabling direct and precise control over pole splitting and fractional bandwidth (FBW). Fabricated and measured results demonstrate excellent in-band performance, achieving a minimum insertion loss of 2.2 dB, a return loss better than 20 dB, and an FBW of 30.5%. Furthermore, a deep stopband rejection exceeding 40 dB is maintained across a wide range from 20.5 to 35 GHz, corresponding to 1.7–2.9 times the center frequency. These outstanding attributes demonstrate that the proposed BPF offers a low-loss, highly selective passive filtering solution well-suited for next-generation RF front-end modules.