A Non-Quadrature Vector Modulator Approach for Wideband Phased Array Systems

Abstract

Phased array systems are widely used in wireless/satellite communication, as well as radar systems, to improve data rate, Signal-to-Interference Ratio (SIR), and Signal-to-Noise Ratio (SNR), thereby enhancing the system's Quality of Service (QoS). RF phase shifters are essential to the operation of phased array systems. The production of phase array components, including antennas, is relatively cost-effective thanks to the advancement of printing manufacturing technology. However, the design of cost-effective RF phase shifters remains challenging in implementing phased array beamformers. Additionally, new-generation telecommunication and radar systems often require stringent phase shifter performance metrics, such as phase resolution and bandwidth, to perform fine beam scanning, which helps increase pointing accuracy. Meanwhile, practical phase shifters display limited performance. On the one hand, On-chip passive phase shifters offer low power consumption and high linearity, but suffer from low resolution, large chip area, and high insertion loss. On the other hand, active phase shifters like vector modulators present relatively high gain at the expense of poor linearity, high power consumption, and relatively low resolution. To attain decent performance in phase precision, commercial phase shifters typically use the GaAs or GaN technology to achieve a 360º digital phase shift, which is costly. Additionally, most phase shifters have a fractional bandwidth below 25 %. This dissertation presents a comparative study and classification of state-of-the-art phase shifter designs and investigates the noise and linearity of vector modulator phase shifters. Then, a novel vector modulator phase shifter approach is proposed for the first time to address the phase resolution limitation, high power consumption and narrow bandwidth issues of state-of-the-art phase shifters.

The proposed vector modulator is based on the generation and subtraction of two unbalanced non-quadrature vectors to produce a 360º analog phase range. A PCB prototype designed at 5 GHz center frequency generates more than 360º continuous phase range with a fractional bandwidth greater than 50%. Moreover, an RF module, comprising input and output Single-Pole Double-Throw (SPDT) switches and the proposed vector modulator with amplification, was designed and laid out in the 130 nm BiCMOS technology for phased array transceiver applications. From the results, the 2.66 mm2 RF module exhibits a respective maximum gain and minimum isolation of 3.3 dB and 49.8 dB from 6.4 GHz to 13 GHz. In addition, an input 1-dB compression power and third-order intercept point (IP3) of 3.78 dBm and 9.1 dBm, respectively, were obtained at the center frequency. Furthermore, the novel X-band non-quadrature vector modulator generates a phase range of more than 360º with a 68% fractional bandwidth, while consuming 18.9 mW of DC power and occupying an area of 1.6 mm².