Frequency Multiplier-Based RF Beamforming Front-End for Vector Modulated Signal Transmission

Abstract

In the rapidly evolving era of wireless communications, the advent of sixth-generation (6G) technology promises unprecedented advancements in terms of high data rates and ultra-low latency, which will lead to significant improvement in different applications such as internet-of-things, autonomous driving, and virtual/augmented reality. The key enabler for these advancements lies in exploiting the untapped spectrum bands at millimeter-wave (mm-wave) and sub-terahertz (sub-THz) frequency bands to meet the new stringent data rate and latency requirements. Nevertheless, generating highly-efficient vector modulated signals at these elevated frequency bands face different challenges. For example, the increased free-space path loss and the degradation of the RF performance of most semiconductor technologies at these bands hinder the generation of high-quality signals with sufficient output power. Additionally, vector modulated signals suffer from a high peak-to-average-power ratio, necessitating more strict linearity requirements. Therefore, in light of these challenges, the development of transmitter front-ends capable of surmounting these obstacles becomes imperative to meet the stringent demands of high data rates and ultra-low latency of future wireless communication. The aim of this thesis is to develop a frequency multiplier-based (FM-based) RF beamforming front-end suitable for high-frequency vector modulated signal transmission and to design frequency doublers capable of generating such signals with adequate output power, power efficiency, and linearity. This work begins with proposing a new design methodology for designing high-efficiency frequency doublers with improved AM-PM characteristics. Using the proposed methodology, frequency doublers targeting an output frequency of 60 GHz were designed. Their measurement results showed promising RF performance in terms of output power, power efficiency, and conversion gain. Moreover, by employing digital pre-distortion (DPD) linearization technique, the fabricated designs were able to generate vector modulated signals with acceptable error vector magnitude (EVM) and average efficiency. Next, the work delves into the design considerations of the phase shifters in the context of an FM-based front-end. Accordingly, an RTPS tailored for the FM-based front-end was designed, and its performance was validated experimentally. Subsequently, a V-band RF beamforming front-end module prototype was developed. Its measurement results showed the ability to cover a 360 phase tuning range with high gain and phase accuracy. Also, it effectively generated a vector modulated signal with a flat EVM across the full 360. Lastly, this work advances to even higher frequencies by designing frequency doublers targeting the D-band frequency range. The transition to higher frequency evolved different design challenges. Hence, a novel design approach for designing frequency doublers was developed. The proposed approach was applied to the design of two frequency doubler prototypes targeting an output frequency of 120GHz. These prototypes were validated experimentally, reporting promising output power and power efficiency at the D-band frequency range. Also, by utilizing the DPD linearization technique, they successfully generated vector modulated signals with acceptable performance metrics at this elevated frequency range.