Design and Characterization of a Three-layer PCB Low-pass Filter for Enhanced Harmonic Suppression in Wi-Fi Frequency Bands: An Application of Characteristic Mode Analysis

To address the low-cost demands for harmonic suppression in WLAN circuits, this paper proposes a Printed Circuit Board (PCB) based low-pass filter aimed at harmonic suppression in the Wi-Fi frequency spectrum. The filter is designed with a three-layer structure to enhance its performance and efficiency in high-frequency applications. To gain an in-depth understanding of the filter’s operation and optimize its design parameters, Characteristic Mode Analysis (CMA) were employed. The CMA method not only enables precise prediction of the filter’s frequency response but also assists in identifying and exploiting the principal modes in the electromagnetic field to optimize filtering effectiveness. This approach allows us to accurately control the filter’s cutoff frequency and insertion loss, achieving effective suppression of undesired harmonics in the Wi-Fi band. Simulated and experimental results show that this design markedly improves signal quality and system stability, with an insertion loss of 0.2 dB in the 4–6G Hz passband and harmonic suppression exceeding 20 dB in the 10–20 GHz range, offering valuable insights for the development of future high-performance, low-cost wireless communication systems.