A 38-GHz 32-Element Phased-Array Transmitter Based on Scalable 8-Element Phased-Array Modules for 5G MMW Data Links

This paper presents a 38-GHz 32-element phased-array Tx (transmitter) for the 5G millimeter wave (MMW) communications. The 8-element phased-array Tx modules with 2 GHz IF/5 GHz LO are implemented, and four pieces of the module are stacked to realize an 8×4 brick array. The 38 GHz measurements of the 32-element Tx show 41.8 dBm EIRP at $OP_{1dB}$ with -41.8 dBc image rejection ratio (IMRR) and -35 dBc ×8 LO rejection ratio (×8 LORR). The EIRPs at $OP_{1dB}$ in beam scanning around ±60° azimuth/± 30° elevation planes are 41.8 to 38.3 dBm. The Tx is utilized for data links with a horn antenna module in 35 m that demonstrates 256 QAM/100M-BR (baud rate) with -33.1 dB EVM. The data links of the Tx with a 4-element phased-array Rx (receiver) in 6 m demonstrates 64 QAM/200M-BR with -26.4 dB EVM. The scalable Tx module shows potential for 5G sub-6 GHz/MMW coexistent applications and can be expanded as a massive phased-array using the simple/low-cost stacked methods.

I. Introduction

The 5G sub-6 GHz mobile communication is going to be commercialized in 2020, and 5G MMW communication will launch following sub-6 GHz as advanced applications. For base station (BS) configurations, the IF/LO frequencies of MMW systems should be lower than 6 GHz since they are compatible with the established sub-6 GHz systems [1]–[3]. Besides, in 5G MMW transceivers, phased-array modules integrated with 4-channel beamformer ICs and broadside radiated patch antennas in a PCB as the tile arrays are the conventional type for large-scale arrays (32+ elements) with very compact physical sizes [1]–[2], [4]–[5]. However, the number of antenna elements is restricted by the initial PCB/array design which is unable to be extended for the more elements, and the small PCB size with lots of ICs suffers a thermal issue. On the other hand, phased-array modules using end-fire radiated antennas can be integrated into a massive-array with multiple “stacked” modules as brick arrays, and the thermal issue is alleviated for heat convection between gaps of the separated PCBs [6]–[7].