Xiaohan Zhang

This article presents the design and evaluation of a millimeter-wave (mm-Wave) antenna subset modulation (ASM) transmitter (TX) array. The array consists of an application-specific integrated circuit (ASIC) packaged with on-board antennas, operating in the 28-GHz 5G NR band. For each transmission symbol, the ASM array dynamically selects a subset of antennas for radiation, leading to scrambled I/Q symbols outside the intended direction and thereby enabling resilience against eavesdropping attacks. Compared with prior efforts in this space, which suffer from compromised radio performance and insufficient confidentiality against intelligent eavesdroppers, our system incorporates three key ASIC and antenna innovations, achieving a high level of security protection with minimal performance overhead and development overhead. Specifically, we integrate an on-chip high-speed true random number generator (TRNG), achieving I/Q symbol scrambling in a truly random fashion at the symbol rate. As a result, it is almost impossible for eavesdroppers to predict any future antenna subset (AS) selections, even with the knowledge of all transmitted symbols in the past. In over-the-air (OTA) measurements, the ASM TX array is able to support 1.2-Gb/s 64-QAM communication with a sharp information beamwidth (IB) of $\pm$ 2 $^{\circ}$ , while achieving competitive radio performance on par with state-of-the-art 28-GHz CMOS phased-array transceivers. To the best of our knowledge, this is the first demonstration of incorporating ASM into the existing mm-Wave communication frameworks. Our results highlight the great potential and practicality of integrating ASM technology into future mm-Wave radios.

This article presents the design and analysis of a millimeter-wave (mmWave) four-way Doherty power amplifier (PA), aiming to enhance the PA energy efficiency when amplifying orthogonal frequency-division multiplexing (OFDM)-based 5G new radio (NR) signals with a 10–12-dB peak-to-average power ratio (PAPR). We first introduce a systematic approach to extending a conventional two-way Doherty PA to $N$ ways, followed by a new transformer-based $N$ -way Doherty network synthesis flow. The proposed network synthesis achieves $N$ -way Doherty load modulation using ( $N-1$ ) transformers, one fewer transformer and thus lower loss than conventional designs. In addition, it enables the desired impedance transformation from $R_{\text{ANT}}$ to $R_{\text{OPT}}$ and effectively absorbs the parasitic capacitance of the power cells. Along with the Doherty network, we also introduce a high-speed adaptive biasing circuit, addressing the modulation bandwidth bottleneck in prior Doherty PA demonstrations. As proof of concept, a four-way Doherty PA prototype is implemented in the 47-GHz 5G band (band n262) using the GlobalFoundries 45-nm CMOS silicon-on-insulator (SOI) process. It achieves 24.0-dBm saturated power ( $P_{\text{SAT}}$ ), 23.7-dBm output 1-dB compression point ( $P_{1\,\text{dB}}$ ), 26.8% peak power-added efficiency ( $\text{PAE}_{\text{PEAK}}$ ), 26.3% PAE at $P_{1\,\text{dB}}$ ( $\text{PAE}_{1\,\text{dB}}$ ), 21.7% PAE at 6-dB back-off ( $\text{PAE}_{6\,\text{dB}}$ ), and 13.1% PAE at 12-dB back-off ( $\text{PAE}_{12\,\text{dB}}$ ), demonstrating state-of-the-art performance. In the modulation tests, the PA achieves 14.1-dBm average output power ( $P_{\text{avg}}$ ) and 13.7% average efficiency ( $\text{PAE}_{\text{avg}}$ ) when amplifying a 2000-MHz 5G NR 64-QAM OFDM signal. To the best of our knowledge, this is the first silicon PA demonstration of 2000-MHz channel modulation bandwidth for 5G NR OFDM along with back-off efficiency enhancement up to 12-dB back-off.

This article presents a new notch steering scheme for hybrid beamforming transmitters (TXs) aimed at suppressing spatial interference, thereby enhancing the signal-to-interference-plus-noise ratio (SINR) to support spatial multiplexing. Built upon existing phased arrays, this scheme integrates an auxiliary-path vector modulator (VM) into each antenna element, which in turn, forms an interference-canceling beam. By spatially combining the array factors (AFs) of the main beam and the interference-canceling beam, a deep spatial notch is created while ensuring minimal main-beam power degradation. Unlike the conventional zero-forcing method that requires matrix inversion in digital for spatial notch creation, our scheme enables the computation of antenna weights in analog, significantly reducing the computational cost and latency. Leveraging this new notch steering scheme, we develop a 28-GHz four-element fully connected (FC) hybrid beamforming TX array using the GlobalFoundries 45-nm CMOS Silicon-on-Insulator (SOI) process. It is capable of simultaneously transmitting two independent, wideband data streams (DSs) in the same polarization toward two directions. In probing-based measurements, each TX channel delivers 19.7-dBm OP1 dB, 20.4-dBm $P$ SAT, and 30.6% peak power-added efficiency (PAE) at 29 GHz, demonstrating state-of-the-art TX linearity and efficiency. In over-the-air (OTA) measurements, the packaged TX array achieves 29.8-dBm EIRP1 dB and is able to steer a spatial notch outside the $-$ 10-dB beamwidth of the main beam, with a notch depth of $>$ 35 dB and a main-beam power degradation of $<$ 0.8 dB. Moreover, in spatial multiplexing demonstrations, the TX array is capable of transmitting a 400-MHz 64-quadrature amplitude modulation (QAM) signal to the intended receiver (RX) in the first DS, while suppressing the co-channel continuous-wave or wideband modulated interference created by the second DS with a high SINR.

This article presents a millimeter-wave (mmWave) power-combined Doherty power amplifier (PA) topology. To reach watt-level output power and simultaneously enhance back-off efficiency, we propose a multifunctional PA network based on an extended rat-race coupler, which enables the following: 1) parallel Doherty load modulation; 2) multiway series power combining; and 3) differential to single-ended conversion. As proof of concept, a 38-GHz PA prototype is implemented in the GlobalFoundries 45-nm CMOS SOI process. It demonstrates 27.5-dBm saturated power ( $P_{\rm SAT}$ ), 26.9-dBm output 1-dB compression point ( $P_{1\,\text{dB}}$ ), and 15.0% power-added efficiency (PAE) at 6-dB back-off. Among recently reported 30–50-GHz silicon-based high-power PAs with $>$ 23-dBm $P_{\rm SAT}$ , our design demonstrates the highest $P_{1\,\text{dB}}$ and PAE at 6-dB back-off. Tested under 200-MSym/s 64-QAM modulation, the PA achieves 20.0-dBm average output power ( $P_{\rm avg}$ ) and 12.2% average efficiency (PAE $_{\rm avg}$ ).

This article presents a millimeter-wave (mmWave) three-way Doherty output network and its silicon implementation at 38 GHz for 5G new radio (NR) orthogonal frequency-division multiplexing (OFDM). The proposed network synthesis methodology can realize impedance levels that are close to the ideal three-way Doherty operation, reduce the impedance transformation ratio at back-off, and directly absorb the device’s parasitic capacitance. Its design procedure and tradeoffs are discussed in detail. A 38-GHz power amplifier (PA) prototype is implemented in the GlobalFoundries 45-nm CMOS SOI process, achieving 13.7%/11.0% power-added efficiency (PAE) at the 9.5-/11.5-dB back-off, which is among the highest compared with recently reported silicon PAs operating at 35 GHz and above. Tested under 1- and 2-component carrier (CC) 5G NR FR2 64-QAM OFDM signals in the Band n260, the PA demonstrates state-of-the-art average output power (11.3 dBm) and average efficiency (14.7%) with −25-dB error vector magnitude (EVM). The design robustness and reliability are further demonstrated through the testing of multiple samples and PA lifetime.