High-Efficiency Low-Pass Reflectionless Filter Based on Modal Decomposition and Electromagnetic Absorber

The article introduces a novel, highly miniaturized, low-pass reflectionless filter that leverages electromagnetic absorber and modal decomposition technologies. The filter is implemented on an FR-4 printed circuit board that has compact external dimensions (
$13.5\times 12.7\times0.25$
mm), and it is coated with an elastic magnetodielectric material with a thickness of 0.5 mm. The filter is investigated by employing electrodynamic simulation using finite difference time domain (FDTD) in Keysight EMPro and by testing a manufactured prototype. Measurement demonstrates that the proposed device has a passband of 0.7 GHz and a wide stopband. The value of
$S_{21}$
does not exceed -20 dB in the frequency range from 2 to 7 GHz, and in the frequency range from 7 to 20 GHz, the value does not exceed -40 dB. Additionally, the standing wave coefficient in the passband remains below 1.5. The value of
$S_{11}$
does not exceed -12 dB in the full range. Broadband and narrowband interference suppression efficacy is assessed through N-norms analysis. Signal integrity is evaluated by exciting a pseudorandom bit sequence at 1 and 2 Gbps at the filter input. N-norms and eye diagrams confirm that the filter can successfully safeguard signal circuits against intentional electromagnetic interference (IEMI). In addition, its efficacy in suppressing broadband and narrowband interferences is compared with 25 existing filters. As a result, simulating frequency characteristics and calculating N-norms of the output responses reveal that the proposed filter outperforms analogs in suppressing both types of IEMI.