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.

I. Introduction

Electronics are widespread in many systems such as industrial, aerospace, automotive, energy, and telecommunications. As a consequence, the safety and stability of all industries, especially critical ones, depend on the proper functioning of electronics [1]. This problem is aggravated by the increasing design complexity of electronic circuits, the increasing total number of simultaneously operating components, the increasing upper frequencies of useful signals, and the increasing power of radio transmitters. In addition, the performance of electronics is affected by susceptibility to electromagnetic interference (EMI). This is an important factor, especially given the increasing performance of intentional EMI generators [2]. Conductors in printed circuit boards (PCBs) and integrated circuits, power supply buses, and connectors are effective antennas capable of interference reception that propagate by conductive means [3]. For example, in power circuits, increasing the switching speed leads to EMI problems [4]. In automotive systems, due to the high level of integration of circuits and systems on the PCB, interconnect design has become a critical parameter [5]. It is important to note that it is necessary to design circuits with conductive interference protection in mind from the early stages of development [6]. There are a number of measures currently available to improve the susceptibility of electronics to interference. These measures are designed to minimize EMI excitation and ensure proper operation and reliability of electronic systems. Some of these measures include shielding, filtering, grounding, component selection, etc.