Compact Superdirective Microstrip Antenna Array Using Capacitively Loaded Loops on High-Dielectric Substrate

To address the fundamental tradeoffs between antenna efficiency, directivity and size of superdirective antennas, a compact microstrip antenna array using a high- dielectric substrate (
ϵ
_r
= 24) is presented. Leveraging the quasi-Yagi–Uda principle, we construct the antenna elements using capacitively loaded loops (CLLs) and arc-shaped monopoles for high directivity. A pair of monopoles are placed in parallel to achieve good impedance matching. A two-element superdirective antenna array is designed based on the magnetic coupled mode. The antenna elements perpendicularly stand on the metal ground face to face, and a power divider is introduced for equal amplitude and in-phase excitation through the respective arc-shaped monopoles. The maximum directivity is achieved when the antenna elements are in resonance, where the distance between the monopole elements is optimized to be 24 mm for the maximum directivity of 7.32 dBi.