Dual-Polarized Patch Antenna Array Integrated with Capacitive Proximity Sensor for 5G Millimeter-Wave Smartphones

We present a novel concept of a millimeter-wave patch antenna that integrates the functions of a dual-polarized antenna and a capacitive proximity sensor to detect the state of a hand grip on a smartphone and compensate for the effect. The antenna has a dual-polarized, proximity-coupled, square patch structure, and acts as a proximity sensor by utilizing the change in capacitance of the patch when the user's hand approaches. By observing the change in capacitance at the center of a square patch operating in two fundamental TM modes, antenna and sensor functions can be performed concurrently and without mutual interference. The antenna is designed using a low-cost four-layer FR-4 substrate and fabricated using a cost-effective standard printed circuit board (PCB) process. The antenna is configured as a 1 \times 8$ array, and after mounting it on a smartphone model, the gain, beam steering performance, and change in capacitance according to hand proximity are predicted and measured. The peak gain measured at 28 GHz exceeds 11.8 dBi, with a gain variation of less than 2.2 dB within the 5 G 257 band (26.5-29.5 \mathrm {GHz}$ ). The measured capacitance change due to hand proximity is 130 fF, which is sufficient for real-time detection of the hand grip state. An example of improvement in the gain of the proposed antenna by detecting the hand grip state is presented through a simulation.