Compact Self-Shielding Components for Beamforming Networks Implemented in Substrate Integrated Coaxial Line Technology

A substrate integrated coaxial line (SICL) technology implemented in standard printed circuit board (PCB) technology is proposed to realize shielded miniaturized millimeterwave (mmWave) components, eliminating spurious feed network radiation that may influence the antenna array’s radiation pattern. Additionally, coupling to neighboring signal lines is avoided by the self-packaging characteristic of SICL lines, thereby minimizing undesired crosstalk in the routing network. A thorough comparison to more traditional transmission lines, such as grounded co-planar waveguides (GCPWs), shows excellent packaging behavior by minimizing radiation and increasing the routing flexibility between the compact functional components. Further validation of this technology is done by implementing several essential components for beamforming networks: a coaxial via transition, a packaged hybrid coupler and an improved, miniaturized hybrid coupler with direct interfacing. The proposed shielded coaxial via transition from SICL to SICL exhibits a measured insertion loss smaller than 0.74 dB in a broad operational frequency range from 23.75 to 32.5 GHz (31%), covering the n257, n258, and n261 5G bands. In this frequency range, the (miniaturized) SICL hybrid coupler has a measured amplitude imbalance (AI) below 1 dB (0.8 dB) and the phase imbalance does not exceed 6° (3°). The proposed miniaturized SICL hybrid coupler has a footprint of only 4 mm in diameter.