Reflectionless Low-Pass Filters Based on Reflection Symmetric Structure for IEMI Suppression

This article presents reflectionless low-pass filters based on a reflection symmetric structure for suppressing intentional electromagnetic interference (IEMI). The protective structures can attenuate ultra-wideband (UWB) and narrowband (NB) IEMIs, and their potential application is investigated. The frequency and time characteristics of the structures are examined in terms of suppressing IEMI and maintaining signal integrity. Full-wave electrodynamic simulation was performed using the finite element method in the frequency range of 0–10 GHz. To verify the simulation results, prototypes were fabricated, and their S-parameters were measured using a vector network analyzer. The results indicate that the structures have a passband of 1.37 GHz for the modal filter (MF) and 0.8 GHz for the meander line (ML). The value of S₂₁ for both structures does not exceed −15 dB in the frequency range from 3.5 to 10 GHz. In the full frequency range, S₁₁ does not exceed −15 dB. The comparative analysis of IEMI suppression using these filters demonstrated that the structures offer advantages in terms of attenuating conducted UWB and NB IEMIs according to the analysis of five standard N-norms. The results indicate that all proposed structures can suppress IEMI with different spectra, but the ML structure showed the best suppression performance. However, this resulted in a reduced bandwidth of the ML. The simulation with data rates normalized to the bandwidth of each filter demonstrated that the MF provides higher signal transmission quality.