Highly Selective Compact Cascaded Suspended Stripline Bandpass Filter

Abstract

This letter presents a novel compact, highly selective, wideband (WB) bandpass filter (BPF) based on the suspended substrate stripline (SSS) technique, realized by cascading a low pass filter (LPF) and a high pass filter (HPF) for $K_{u}$ -band applications. To enhance compactness without compromising the filter specifications, the longest stubs in the layout were minimized to their shortest feasible lengths. The filter operates within a passband of 13–14.8 GHz, achieving a fractional bandwidth of 13%. Schematic and electromagnetic (EM) simulations were conducted using the Advanced Design System (ADS) software, and the corresponding layout sections were fabricated on a 5-mil RT/Duroid 5880 substrate, which has a compact footprint of $2.7\times 1.4$ cm². The scattering parameter responses of the fabricated filter were measured, demonstrating an insertion loss (IL) of 1.5 dB within the passband and a return loss (RL) of approximately 15 dB. Furthermore, the design achieves a sharp rejection greater than 60 dB at a frequency offset of 4% from the band edges and maintains a wide stopband extending up to 24 GHz with a minimum rejection of 30 dB.