A Helmet-Based Hemispherical-Conformal Wearable Array Antenna With Broad Bandwidth, Wide-Angle Coverage, and Reconfigurable Dual Circular Polarizations for WBAN Applications

This article presents a helmet-based hemispherical-conformal wearable array antenna with broad bandwidth, wide-angle coverage, and reconfigurable dual circular polarizations (CPs) that is suitable for wireless body area network (WBAN) applications. First, a broadband and polarization-reconfigurable conformal radiating element is designed, which features a single-feed reconfigurable crossed dipole incorporated with parasitic patches above a ground plane for attaining unidirectional radiations. By integrating four p-i-n diodes on four arms of the crossed dipole, the element can flexibly switch its polarization states among two orthogonal CP modes. Four sector-shaped parasitic patches placed in four quadrants of the crossed dipole help to expand the operating bandwidth. Furthermore, we design a 12-element helmet-based hemispherical-conformal polarization-reconfigurable wearable array that is arranged in a special configuration for increasing the gain, coverage range, and orientation flexibility for WBAN systems. The measured results show that the proposed conformal wearable array exhibits an overlapped 3-dB axial ratio bandwidth (ARBW) of up to 29.6% and −10-dB impedance bandwidth (IMBW) of 69.8% at around 3 GHz for two reconfigurable CP modes. Besides, it has a relatively wide beam coverage range of $110^{\circ } \times 360^{\circ }$ and a peak measured gain of more than 8 dBi for both polarization modes.