Design of a Pattern-Reconfigurable Wearable Planar Dipole Antenna Based on the Yagi-Uda Antenna Principle

With the deep penetration of Wireless Body Area Network (WBAN) in scenarios such as medical monitoring and sports health, there is a growing demand for wearable patch antennas that offer enhanced directional performance and flexibility. This paper presents a novel pattern-reconfigurable planar dipole patch antenna designed for the 5 G N79 band (4.4–5 GHz). The proposed design incorporates a reconfigurable balun structure and four parasitic metal strips loaded with PIN diodes for beam control. By switching the diodes ON or OFF, the parasitic strips can function either as reflectors or directors, enabling four-directional beam reconfiguration. In free space, when the antenna operates in State 1 or State 4, it attains an impedance bandwidth of 174 MHz (4.389–4.563 GHz), and when operating in State 2 or State 3, it reaches an impedance bandwidth of 149 MHz (4.363–4.512 GHz). The antenna features a compact size of 1.02 × 1.02 × 0.22 λ₀³ and achieves the measured peak gain of 5.084 and 4.463 dBi in State 1 and State 2, respectively. The measurement results are in good agreement with the simulation results, and both the S₁₁ parameters and the radiation patterns meet the expected performance. In addition, when the antenna is placed close to the human body, the low Specific Absorption Rate (SAR) values demonstrate its safety for wearable applications.