Beam steering characteristics and element failure compensation of spatially superposed M-ary modulation system

We present a new wireless communications system featuring a novel M-ary modulation scheme that uses spatial-power combining technology instead of two amplitude-modulated carriers in quadrature. The system incorporates multiple QPSK modulators and two-beam simultaneous transmission. Their modulator output signals are fed to power amplifiers, where each QPSK signal is separately power amplified with high efficiency. The system enables spatial superposition of two beams efficiently by using a specially tailored circular array system. One of the features in the array system is the beam steering function. We investigated the allowable beam steering angle to satisfy the required spatial superposition and showed that the spatial superposition was achieved within the range of about +/- 8 degrees from the center when the two beams were steered by 10 degrees. We also investigated the effect of gain/phase setting errors evident among array elements and clarified that the spatial superposition angle of 5 degrees can be attained even when a gain setting error of 1 dB and a phase setting error of 15 degrees are evident. In addition, we studied the effect of the failure of elements constituting our system on spatial superposition and created a compensation method to maintain the performance after the elements fail. We found that our system was feasible and reliable and enabled broadband transmission with efficient use of power and bandwidth.