Differential tunable phase shifter

This b paper describes theoretical study, modeling and simulation of tunable coupled line phase shifter. This structure is based on basic Schiffman model in which a coupled dispersive microstrip transmission line was used combined with uniform transmission line. The main idea of this work is to design a mixed structure of tunable phase shifter loaded by Varactor diode. A differential phase between two paths of transmission signal was created and tuned using variable capacitance, this phase keeps approximately the same value on the operating frequency band between 0.8 and 1.4GHz. We have evaluated the performances and good variation of phase shifting was denoted with good insertion loss, less than 1.0dB and return losses for both of two signal paths.