Constant–ε_r Lens Beamformer for Low–Complexity Millimeter–Wave Hybrid MIMO

It is well established that the utilization of unused millimeter–wave (mmWave) spectrum is inevitable due to unavailability of required bandwidth in the conventional RF band to support the high data demands of 5G. Large antenna arrays with beamforming capabilities are required to compensate for the high path–loss at mmWave frequencies. We are at the verge of a massive mmWave radio front-end deployment and low–complexity low–cost hardware beamforming solutions are required now at this stage than ever before. In this work, one such solution is demonstrated and analyzed. A high performance and low–complexity lens based beamformer consisting of constant dielectric material (r) with antenna–feeds is presented for multi– beams operation. A prototype is developed based on the classical synthesis approach, and in line with the requirements of mmWave hybrid multi–user multiple–input multiple–output (MU–MIMO) systems. A characterization at 28 GHz is performed wherein uplink signal–to–noise–ratio of user terminals is evaluated with the zero–forcing (ZF) baseband signal processing. Radiation performance of a single source beamformer is measured in an anechoic environment and end–to–end ergodic sum spectral efficiency performance is estimated based on the measured data. It is shown that the constant–r based beamformer solution is simple, yet significantly outperforms conventional antenna array beamformers with analog phase shifter network, making it a promising candidate for future hybrid massive MIMO systems.