Superdirective Unidirectional Mixed-Multipole Antennas: Designs, Analysis, and Simulations

Highly directive antenna systems that will address the needs of space-limited Internet-of-Things (IoT) devices and their NextG applications are in demand. Compact high-frequency high-directivity alternatives to complex, power-hungry phased arrays are desired. Several compact, unidirectional mixed-multipole antennas (UMMAs) based upon mixtures of primarily dipoles and quadrupoles are reported. The simulated performance characteristics of these 28-GHz near-field resonant parasitic (NFRP) antennas, notably their large peak directivities and front-to-back ratios (FTBRs), are presented; they are all demonstrated to be superdirective while having attractive radiation efficiencies. Uniform endfire arrays of active closely spaced equal-length idealized wire dipoles are exemplified as reference cases. The Rayleigh quotient (RQ) method typically used to determine their amplitude coefficients is extended for the first time to achieve unidirectional versions. Comparisons between these unconstrained and constrained RQ-designed arrays are made. While the performance characteristics of the single-source broadside-radiating UMMAs approach those of the reference arrays, a direct comparison of a realizable UMMA with the analogous unequal-length, nonuniformly spaced idealized dipole array demonstrates its superiority. A two-element UMMA array that is scalable to a larger number of elements is also presented and shown to be superdirective, illustrating that the attractive properties of its individual elements are maintained even when mutual coupling occurs.