Superdirective, Electrically Small, Endfire-Radiating Huygens Quadrupole Antenna

A self-resonant electrically small endfire-radiating Huygens quadrupole antenna is designed and experimentally validated to have superdirective performance. It consists of two near-field resonant parasitic (NFRP) Huygens dipole radiators (HDRs) excited by a single-feed electric dipole. Both seamlessly integrate a rectangular Egyptian axe dipole (EAD) element acting as the electric dipole together with a specially engineered, folded capacitively loaded loop (CLL) element serving as the requisite orthogonal in-phase magnetic dipole. Orientation reversal of one HDR facilitates both radiating their unidirectional fields in the same direction. They are arranged in a planar two-element Yagi endfire configuration. Theoretical analysis underscores the quadrupole nature of the design. A prototype of this Huygens quadrupole electrically small antenna (HQ-ESA) was fabricated with 3-D-printing, assembled, and tested. The measured results, in good agreement with their simulated ones, confirmed that a high directivity of 7.61 dB, high realized gain (RG) of 7.06 dBi, high overall efficiency (OE) of 88.1%, and front-to-back ratio (FTBR) of 8.1 dB were realized even with its electrically small size: ka =0.98. These admirable properties are used to explicitly demonstrate that it is a superdirective system. Comparisons with reported single-feed ESAs and two-element superdirective parasitic arrays further highlight the superiority of its performance metrics.