End-Fire Gain Enhancement Using Symmetrical Director Pairsfor 28 GHz RF Systems

Abstract

This paper presents a gain-enhancement technique for a compact and low-profile dipole–Yagi antenna operating at 28 GHz for millimeter-wave 5G applications. Unlike conventional Yagi–Uda antennas, where director elements are arranged in a single plane, the proposed design employs symmetrically paired directors placed on both the top and bottom layers of the antenna structure. These director pairs are strategically positioned away from the conventional central front region of the driven dipole, leading to improved electromagnetic field confinement and enhanced end-fire radiation. Based on this concept, a four-element end-fire array antenna is designed, fabricated, and experimentally validated. The measured results, including reflection coefficients, radiation patterns, and realized gain, show good agreement with simulations, confirming stable impedance matching and strong directional performance across the 28 GHz band. Furthermore, the multiple-input multiple-output (MIMO) performance of the array is evaluated for smartphone and compact RF system applications, demonstrating satisfactory diversity characteristics. Owing to its high gain, compact size, low-profile structure, and favourable MIMO performance, the proposed antenna represents a promising solution for millimeter-wave instrumentation systems.