Improving the Performance of Antenna-on-Chip by Effectively Illuminating the Artificial Magnetic Conductors through Coupling Enhancement Structures

An antenna-on-chip (AoC) suffers from low radiation efficiency and gain because of the highly conductive silicon substrate used in standard complementary metal–oxide–semiconductor (CMOS) processes. Placing an artificial magnetic conductor (AMC) surface underneath the AoC not only isolates the antenna from the lossy substrate but also boosts its performance through in-phase reflection. Ideally, the AMC, which has a periodic structure, should be infinite in size, but practical chip sizes limit its dimensions. The gain of an AMC-backed AoC shows a positive correlation with the AMC lateral area. However, in the ultrathin stack-up of standard CMOS processes, the AMC cannot be irradiated uniformly by the antenna because of the physical illumination issue, so the AoC gain does not increase with the AMC area after the initial increase. To improve the illumination of the AMC by an AoC, this work introduces coupling enhancement structures (CES) that employ the available metal layers of the stack-up. The proposed AMC-backed AoC with CES demonstrates a gain of 9.8 dBi and radiation efficiency of 71% at 94 GHz, which are improvements of 4.3 dB in gain and 23% in radiation efficiency, respectively, compared to an AoC backed by a conventional AMC.