A 28-GHz Phased-Array Receiver Front End With Dual-Vector Distributed Beamforming

This paper presents a 28-GHz four-channel phased-array receiver in 130-nm SiGe BiCMOS technology for fifth-generation cellular application. The phased-array receiver employs scalar-only weighting functions within each receive path and then global quadrature power combining to realize beamforming. We discuss both the theory and nonidealities of this architecture and then circuit design details for our phased-array front-end prototype. Differential low-noise amplifiers and dual-vector variable-gain amplifiers are used to realize each front end in a compact area of 0.3 mm². Across 4-b phase settings, each array element achieves 5.1-7 dB noise figure, -16.8 to -13.8 dBm input-referred 1-dB compression point, and -10.5 to -8.9 dBm input-referred third-order intercept point. The average gain per element is 10.5 dB at 29.7 GHz, whereas the 3-dB bandwidth is 24.5% (26.5-33.9 GHz). Root-mean-squared gain and phase errors are less than 0.6 dB and 5.4° across 28-32 GHz, respectively, and all four elements provide well-matched and well-isolated responses. Power consumption is 136 mW per element, equaling 546 mW for the four-element array.

I. Introduction

Future cellular systems will support higher capacity along with faster peak- and edge-data rates. This need has the potential to be partially met by shifting toward millimeter-wave frequencies [1], [2]. In particular, the 28-GHz frequency band is an attractive candidate for fifth-generation (5G) networks due to available spectrum, favorable channel characteristics [3], [4], and the ability to realize highly integrated high-performance hardware in silicon [5]–[8]. Link budgets for 28 GHz [1] suggest moderate beamforming for user equipment (one to eight elements) and stronger beamforming at the basestation (up to hundreds of elements).