A 2–20-GHz 360° Variable Gain Phase Shifter MMIC With Reverse-Slope Phase Compensation

This paper presents a 2–20-GHz highly accurate vector-sum variable gain phase shifter (VGPS) monolithic microwave integrated circuit (MMIC) for ultra-broadband phased-array applications. An active power splitter followed by a dual-path I/Q network is utilized for precise I/Q signals generation. A reverse-slope phase compensation technique is proposed to improve broadband I/Q phase balances. Two active single-to-differential convertors further divide the I/Q signals into four quadrature signals. The vector modulator consisting of variable gain amplifiers (VGAs), passive analog adder and differential-to-single convertor synthesizes the desired output phase with tunable gain by orthogonal modulation and summation of the four quadrature signals. The designed VGPS, fabricated in 0.25- $\mu \text{m}$ GaAs pHEMT technology, achieves 360° of full-span phase shift with tunable gain and a one-decade instantaneous bandwidth. Measurement result shows that the peak gain and input referred 1-dB compression point of the proposed VGPS are–3.1-dB and +6.5-dBm, respectively. With the aid of off-chip frequency-independent logic circuits and digital-to-analog convertor (DAC), the VGPS exhibits 6-bit phase resolution with root-mean-square (RMS) phase error of less than 2.92°over 2–20-GHz. The VGPS also results in a 4-bit gain control performance with 7.5-dB gain tuning range (RMS gain error < 0.34-dB) and a 5-bit gain control performance with 15.5-dB gain tuning range (RMS gain error < 0.62-dB). The VGPS MMIC consumes 115-mA current from a 5-V voltage supply and occupies chip area of 4.5-mm2 (excluding pads).