Compact S-Band Low-Pass Filter with Enhanced Suppression using Inductive Compensated Resonators and BSF Feed Line

This paper presents an innovative technique for designing a compact L-band and S-band microstrip low-pass filter (LPF) utilizing cascaded resonators with doubly inductive compensated coupled lines. The proposed design significantly enhances signal suppression in the transition and stopbands compared to conventional stub-based LPFs. A closed-form design equation is provided for ease of implementation. Simulation and experimental results for a 2.75 GHz cut-off frequency LPF demonstrate an insertion loss of less than 0.1 dB, return loss exceeding 24 dB, and suppression performance over 52 dB at 5.5 GHz. The compact size and superior suppression performance make this filter ideal for modern microwave systems.