A Millimeter-Wave Distributed Transmitter Beamforming Array in SiGe BiCMOS Technology

This article presents the design, implementation, and experimental evaluation of a custom-designed chip-scale distributed transmit beamforming (DTB) array operating at millimeter-wave frequencies. Each transmitting node incorporates a phase-locked loop (PLL), a phase shifter, and a power amplifier, all fabricated using a 0.13- $\mu \text {m}$ SiGe HBT BiCMOS process. The transmitters are packaged with a custom high-gain patch antenna array to enable millimeter-wave signal transmission. Wireless coherent beamforming was experimentally demonstrated using an array of spatially distributed transmitter nodes synchronized to a common reference signal. The array achieves over 93% of the ideal coherent gain. Solid frequency synchronization was achieved using the on-chip PLLs, resulting in a stable signal with improved phase noise results after beamforming. In addition, a comprehensive analysis of phase noise in DTB arrays is presented and experimentally validated, demonstrating near-theoretical and repeatable phase noise improvements. The impact of frequency synchronization errors and receiver displacement on signal integrity is also investigated, emphasizing the critical role of precise phase and frequency synchronization.