A Low‐Cost Via‐Less Air‐Filled Waveguide in Multilayer PCB for High‐Frequency Circuits Based on Artificial Magnetic Conductors

Abstract This paper proposes a novel, low‐cost, AMC‐based via‐less approach to implementing air‐filled waveguides (AFWs) embedded within multilayer printed circuit board structures to achieve low propagation loss. Three layers of low‐cost FR4 substrates are sandwiched together using prepreg to form the basic AFW structure. To overcome the technical impossibility of seamless vertical metalization in multilayer LCP or FR4 processes, an electroplating technology combined with planar artificial magnetic conductor (AMC) surfaces is employed to construct the waveguide sidewalls. The AMC structures effectively create a virtual magnetic wall that suppresses electromagnetic (EM) leakage through the unplated prepreg layers. To further enhance field confinement and reduce junction leakage, a modified AMC structure incorporating longitudinal metal strips is introduced. Numerical simulations at 77 GHz demonstrate that the proposed AFW achieves a remarkably low theoretical propagation loss of 0.08 dB/cm. A prototype was fabricated and measured to validate the design. While transition‐region fabrication sensitivities affected the absolute insertion loss, the intrinsic propagation loss of the waveguide core was extracted using a multi‐length transmission line method, yielding an experimental result of 0.16 dB/cm. The proposed architecture provides a highly integrable, cost‐effective, and high‐performance solution for millimeter‐wave (mmWave) and sub‐terahertz applications, such as automotive radar and 5G/6G communications, where traditional substrate‐integrated waveguides (SIW) suffer from high dielectric losses.