Dual-Band Circular-Polarized Microstrip Antenna for Ultrawideband Positioning in Smartphones With Flexible Liquid Crystal Polymer Process

This article proposes a dual-band circular-polarized (DBCP) microstrip antenna using flexible liquid crystal polymer (LCP) manufacturing process for ON-smartphone ultrawideband (UWB) positioning application. To achieve dual-band circular polarization in a low profile, the proposed antenna is designed with a cross-slot-loaded patch with four L-shaped feeding probes and a sequential phase feeding network. A circle of capacitive via fence is loaded surrounding the patch for area miniaturization, which is adaptive for the limited space of flexible printed circuit (FPC) in smartphones. Based on the UWB positioning protocol, a three-element antenna array is constructed in a low profile of $0.015\lambda _{0}$ with required isolation of 17 dB. Experimental results show the overlapped bandwidth of the efficiency and the axial ratio (AR) covering the demand bands of 6.30–6.80 and 7.75–8.10 GHz. With the properties of dual wideband operation, circular polarization, and ultralow profile, the proposed antenna exhibits feasible solutions for the UWB positioning application in space-limited smartphones.