Numerical analysis of Huygens-like on-chip antennas for mm-wave applications

As we transition to 5G and beyond, the frequencies increase and the efficiency of the antennas becomes a pressing issue. Silicon technologies are preferred when it comes to en masse user equipment production, but the antennas in silicon suffer from high dielectric losses and strong substrate waves coupling. The use of a Huygens source as the antenna element has a potential of decreasing these negative effects, as was demonstrated in several non-silicon PCB designs. In this paper, we investigate if a similar performance enhancement can be achieved in thin back-gated silicon antenna chips. We present a numerical comparison of an electric dipole, a magnetic dipole and a Huygens source antenna at 120 GHz on a lossy silicon substrate sitting on a ground plane. Antennas are defined in MATLAB as distributed currents and imported as near-field sources into CST Microwave Studio. This way we treat the problem in a very general way without regards for any particular physical antenna implementations. Radiation efficiency and gain are shown as functions of substrate thickness. We found that there is no apparent advantage of using a Huygens source over either electric or a magnetic dipole in the described setup. We argue that this result is based on the fact that the Huygens source is derived assuming infinite current sheets at the interface of two infinite homogeneous regions, and propose another definition for a Huygens source in multi-layer structures