A linear and broadband power amplifier (PA) for 5G phased-array is presented. The design improves the linearity by operating the transistors in deep class AB region. The design broadens the bandwidth by applying the inter-stage weakly-coupled transformer. The theory of transformers is illustrated by analyzing the odd- and even-mode model. Based on this, the odd-mode Q factor is used to evaluate the quality of impedance matching. Weakly- and strongly-coupled transformers are compared and analyzed in both the design process and applicable characteristics. Besides, a well-founded method to achieve the transformer-based balanced-unbalanced transformation is proposed. The fully integrated two-stage PA is designed and implemented in a 65-nm CMOS process with a 1-V power supply to provide a maximum small-signal gain of 19dB. The maximum output 1-dB compressed power (P1dB) of 17.4dBm and the saturated output power (PSAT) of 18dBm are measured at 28GHz. The power-added efficiency (PAE) of the P1dB is 26.5%. From 23 to 32GHz, the measured P1dB is above 16dBm, covering the potential 5G bands worldwide around 28GHz.

Low signal power and susceptibility to interference cause difficulties for traditional global navigation satellite system (GNSS) receivers in tracking weak signals. Extending coherent integration time is a common approach for enhancing signal gain. However, coherent integration time cannot be indefinitely increased owing to navigation bit sign transition, receiver dynamics, and clock noises. This study proposes a cross-correlation phase combining (CPC) algorithm suitable for distributed multi-antenna receivers to improve carrier-tracking performance in weak GNSS signal conditions. This algorithm cross-correlates each antenna’s intermediate frequency (IF) signal and local carrier to detect the phase differences. Subsequently, the IF signals are weighted to achieve phase alignment and coherently combined. The carrier-to-noise ratio (CNR) and carrier phase equation of the combined signal were derived for the CPC algorithm. Global positioning system (GPS) signals received by distributed antenna array with six elements were used to validate the performance of the algorithm. The results demonstrated that the CPC algorithm could effectively achieve signal phase alignment at 32 dB-Hz, resulting in a combined-signal CNR enhancement of 6 dB. The phase-tracking error variance was reduced by 72% at 30 dB-Hz compared with that of a single-antenna signal. The algorithm exhibited low phased array calibration requirements, overcoming the limitations associated with coherent integration time and effectively enhancing tracking performance in weak-signal environments.

A large-range switchable RF signal generator is demonstrated using a triple-wavelength fiber laser with uneven-frequency-spacing. Due to the birefringence characteristics of the triple-wavelength fiber laser, switchable dual-wavelength operation can be obtained by adjusting a polarization controller. Therefore, we can achieve a stable RF signals at microwave or millimeter-wave band.