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-mum 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 360degrees 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 360degrees and 90degrees, 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 min(2), which to our knowledge is the smallest size for a passive reflective-type phase shifter with 360degrees phase-control range reported to date.