Compact Triple-Band Millimeter Wave Flexible Antenna for Wearable Applications

Abstract

With the wide demand for wearable gadgets, flexible antennas have emerged to fulfill the requirement of uninterrupted connectivity with stringent radiation behavior. A compact triple-band antenna is proposed to operate at mmWave band. A liquid crystal polymer substrate is used as it has good mechanical and resistive properties against bending and is very cost-efficient. The chosen dimension of the substrate is $0.635\lambda_{0}\mathrm{x}0.635\lambda 0$, where $\lambda$0 is the lower operating mmWave wavelength. The proposed antenna operates at 31.76 GHz, 34.46 GHz, and 49.87 GHz with good impedance matching, having reflection coefficients of −23.3dB, −15.81dB, and −27.97dB, respectively. The fractional bandwidth of the designed antenna is 10.97%, 0.99%, and 7.45%. The antenna is validated for bending analysis at angle 6 varying from $8.6^{0}$ to $5.7^{0}$ along the two-dimensional axis. The specific absorption rate (SAR) is 3.3 W/kg and 2.14 W/kg at 15 mm and 20 mm distances. The structure has attained the maximum gain of 6.59, 4.54, and 9.25 dBi, respectively. The radiation pattern is bidirectional with HPBW of $44^{0}, 42^{0}$, and $36^{0}$ in the E-plane. The radiation pattern is turned to directional over the phantom model with an HPBW of $20^{0}$ and a maximum gain of 10.4 dBi. Finally, the proposed structure is simulated by placing it over a helmet for military hostile surveillance applications.