Design of tunable phase shifters by the image-parameters method

Based on the image-parameters (IP) method, a design technique is presented for electronically tunable phase shifters consisting of transmission lines periodically loaded with switched inductors and capacitors. The use of both inductors and capacitors allows large phase shifts with low return loss to be achieved, thus leading to very compact devices. Based on the analysis of the IP properties of the elementary cell, the design procedure presented allows an effective control of both the total phase shift and the return loss of the phase shifter, as well as its frequency band of operation. As a proof of concept, experimental test circuits have been fabricated and measured exhibiting a 105deg phase shift with 0.25-dB insertion loss at 4.5 GHz and a return loss of 20 dB over a two-octave frequency band