Compact Triple-Band Millimeter Wave Flexible Antenna for Wearable Applications

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.