Local Oscillator Phase Shifting and Harmonic Mixing-Based High-Precision Phased Array for 5G Millimeter-Wave Communications

This paper presents a 28-GHz low-cost high-precision phased array for fifth-generation millimeter-wave communications. The local oscillator (LO) phase shifting approach and the subharmonic mixing technique are adopted to achieve a full 360 degrees phase-shifting range with up to 10-bit phase resolution and ultralow magnitude deviation. Each phased channel in this array contains a 1-bit 180 degrees intermediate frequency phase shifter and a low-voltage varactor-tuned reflective-type phase shifter at LO path. The LO phase shifting is used to achieve fine phase shifting with low-magnitude variation. The subharmonic mixing enables lower phase range and lower operation frequency at the LO path. The measured root-mean-square phase error and magnitude variation are around 0.3 degrees and 0.1 dB, respectively. The over-the-air phased array calibration and measurement are also performed. The eight-element phased array achieves +/-50 degrees beam scanning angle and fine beam resolution less than 1 degrees step. The gain flatness of the phased array is less than +/-1dB at 1-GHz signal bandwidth. The eight-element array achieves an effective isotropic radiated power of 41 dBm at 10-dB power backoff. The measured error-vector-magnitude is 1.72% with a 500-MHz orthogonal-frequency-division-multiplexing QAM-64 signal.