Ultracompact reflective-type phase shifter MMIC at C-band with 360° phase-control range for smart antenna combining

An ultracompact reflective-type monolithic microwave integrated circuit (MMIC) phase shifter is presented, fabricated using a commercial 0.6-μm GaAs MESFET process. The circuit has been developed for low-cost smart antenna receivers, operating in accordance to the IEEE 802.11a and the high-performance radio local area network (HIPERLAN) wireless network standards at C-band. Capacitance control, required for phase control, is performed by usual MESFETs with capacitance control ratios (C_max/C_min) of less than four. The impact of the reflective terminations on the maximum phase-control range and the corresponding loss is discussed. This investigation comprises single capacitive terminations, single resonated terminations, and terminations with two resonated loads-in parallel (DRL). With the DRL terminations, phase-control ranges of over 360° have been reached even with such limited capacitance control ranges. A transformation network is proposed for the DRL termination to reduce loss and loss variations. In this configuration, maximum signal losses of 9 and 3 dB, and 1-dB input compression points of higher than 2 and 8 dBm were measured for the phase shifter at 5.2 GHz within phase-control ranges of 360° and 90°, respectively. The branch-line coupler of the phase shifter has been realized by using lumped elements, thereby minimizing the circuit size. The total chip area is only 0.9 mm², which to our knowledge is the smallest size for a passive reflective-type phase shifter with 360° phase-control range reported to date