mmWave Antenna Arrays for Early 5G Trials

Abstract

Emerging 5G trials, beginning before standardization, relied on millimeter-wave (mmWave) frequencies to unlock unprecedented bandwidth and data rates. Such early implementations faced significant hardware challenges, including high path loss at mmWave bands and the complexity of large antenna arrays. This study surveys design strategies and subsystem techniques developed prior to 2017 to address these hurdles in early 5G prototypes. Two main architectural directions—phased-array arrays implementing beamforming via hybrid precoding and lens antenna arrays implementing path-division multiplexing—demonstrate compelling trade-offs between RF chain complexity and array performance. Phased-array based hybrid precoding reduces hardware burden by mixing analog beamforming with digital baseband processing, while lens array techniques focus energy based on path direction, enabling lowcomplexity, capacity-approaching MIMO behavior. We review comparative analyses of these approaches, supported by numerical results in pre-2017 literature, and explore antenna array form factors such as SIW (substrate-integrated waveguide) or patch array configurations for mmWave directions. Results show that each configuration improves beamforming gain while managing cost and power. The paper concludes with guidelines for hardware-efficient mmWave antenna array design in early 5G testbeds and contextualizes future work on dynamic beam steering, integration, and hybrid RF architecture.