Near-field Probing Array for Enhancing 5G mm-wave Beamforming Transmitter Performance

Abstract

As sub-6 GHz fifth-generation (5G) communication networks begin to deploy commercially, the industry is seeing a paradigm shift towards the millimeter wave (mm-wave) bands as they provide multi-gigahertz of frequency spectrum and the potential of multi-gigabit data rates with ultra low latency. Intensive research efforts have been put into realizing competitive mm-wave hardware to support the increasing demand for high speed connections and data throughput. This hardware relies on modern semiconductor technologies that still face the challenges of low gain and output power at such high frequencies. When compounded with the high path loss at mm-wave, and the needs of multi-input multi-output operation, the transceivers must be implemented as beamforming phased arrays. Although beamforming phased arrays offer many advantages, there are short-comings associated with them that need to be addressed. In the current landscape, a beamform- ing array with self-calibration capability, linear power amplifier (PA) response, and low production cost is highly desirable. This thesis is written amid these challenges. This work designed and fabricated an antenna-on-PCB (printed circuit board) RF beamforming array at 28GHz with 4 GHz operation bandwidth and +/-50 deg steering range. The array incorporates a novel embedded near-field probing array for the purpose of providing feedback signals for self-calibration and PA linearization using digital pre-distortion (DPD). Using the proposed near-field based calibration procedure, the array output’s amplitude and phase root-mean square variations between elements are 0.27 dB and 2.8 deg, respectively. Using the near-field based DPD, the adjacent channel power ratio and error vector magnitude improved from 30 dB and 8.8% to 39 dB and 2.5%, respectively, for a 400MHz OFDM signal.