Compact variable reflective-type SiGe phase shifter using lumped elements for 5 GHz applications

The design and results of a compact reflective-type phase shifter with transformed single-resonant loads for integrated SiGe phased-array implementations are presented. This circuit has been fabricated using a commercial 0.35 μm SiGe HBT process. A 3-dB 90° coupler with lumped elements instead of microstrip lines is used to allow for a more compact implementation. Phase control is enabled using a SiGe varactor with a capacitance tuning range of only 2.23. Equations are derived to precisely describe the phase control range versus capacitance control range for a transformed single resonated load (TSRL) configuration to allow efficient optimization. It is found that the varactor should be chosen as small as feasible to minimize sensitivity to parasitic resistance. A design procedure for reflective-type phase shifters is given. A phase shifter operating around 4.5 GHz has been designed using the design procedures outlined. The measured phase shift range is 230° for a control voltage varying from 0-4 V.