Microwave endless phase shifter using dual‐gate FET

Abstract

AbstractEndless phase shifters in which phase angles up to 360° can be endlessly varied are required in such areas as space diversity. Conventional endless phase shifters are large in size because they employ waveguides. To make these phase shifters in an MIC form, this paper adopts a method in which the input signal is divided into two with a 90° phase difference and then vector‐combined with appropriate amplitude ratios. To reduce the loss caused by an MIC, we use the dual‐gate GaAs MESFET as an active element. Realization of an FET endless phase shifter requires a dual‐gate FET amplitude adjustment circuit with a small amount of phase shift for a second gate bias. A method of optimizing the second gate terminating impedance to minimize the phase shift has been experimentally studied, although no theoretical analysis is available to date. In this paper, we analyze an equivalent circuit including the bias dependence of the circuit parameters of the FET and numerically compute the amplitude and phase of a dual‐gate FET. The results are compared with those of experiments. It is found that a theoretical design of the second gate terminating impedance is possible. Finally, the results for a fabricated FET endless phase shifter are described.