A.I. Zadorozhnyy

Described here is an analog microstrip phase shifter with required moderate insertion loss level, low cost, and low phase error. The phase shifter is based on varactor diodes and operates in C-band, providing a phase shift of 0 - 360°. To realize a low value of amplitude modulation for different phase states, a two-stage impedance transformation scheme was proposed. This approach is practicable by using low Q-factor diodes. The phase shifter contains two similar reflection phase shifters connected to the coupled and direct ports of a hybrid coupler. Each of the reflection phase shifters includes two tunable resonant circuits and two quarter-wavelength microstrip transformers to transform the input reflection phase shifter impedance compare to 50 ohm transmission line impedance to increase reflection coefficient. The operating frequency range of the phase shifter is bounded by the operating frequency range of the coupler, and equals 8% in C frequency band. The phase shifter module contains a digital control block for reducing the phase error to a minimum determined by the measurement equipment and DAC precision. After phase shift vs. voltage characteristic is measured, it is stored in the digital control block memory cell. Thus, the input control signal is digital (frequency and phase shift digital code). The voltage on varactors is generated by DAC according to the input control signal and memorized data. The described phase shifter was designed for phase array antenna application and has been serially produced. The low phase error and continuous phase shift allows forming the phase array antenna radiation pattern with zeros in noise directions, and enables precision steering.