Flexible Beam Design for Vital Sign Monitoring Using a Phased Array Equipped With Double-Phase Shifters

Recognizing the low-cost advantage of phased arrays, we investigate the improvement of the beamforming capability of a phased array via the use of double-phase shifters (DPS), i.e., each antenna is fed with the sum of the outputs of two phase shifters. The use of DPS allows for the manipulation of both the magnitude and phase of the signal transmitted by each antenna, thus enabling the formation of a flexible beam toward the desired target while suppressing the energy radiated toward unwanted directions. By sequentially steering the mainbeam to each target, while nulling other targets, one can monitor the vital signals of multiple targets with low inter-target interference. This is achieved at only a modest increase in the cost of a phased array due to the addition of phase shifters. The performance of the proposed approach is demonstrated via a prototype DPS phased array with 4 Vivaldi antennas using 8 commercial phase shifters and transmitting a continuous-wave RF signal at center frequency of 2.2 GHz.