IMPROVED MINIATURIZED WIDE-BAND 90-DEGREE SCHIFFMAN PHASE SHIFTER

In a standard Schiffman phase shifter a coupled section and a uniform transmission line are used to give a differential phase shift. In order to achieve larger bandwidth, it is necessary to use tight coupled sections which are difficult to realize especially high phase shift and low permittivity. In this paper, an improved wide-band 90 degrees Schiffman phase shifter is presented by using a back to back microstrip line. In this design, the gap of the coupled lines is larger for matching the microstrip back to back than the coupling between the two transmission lines (coupled and uncoupled) can be neglected. Therefore the size of the Schiffman phase shifter can be reduced. Compared with the former microstrip multisection coupled-line configuration, our newly proposed planar one with back-to-back microstrip line is small in size and, meanwhile, has a good performance. As an example, the improved Schiffman phase shifter is simulated. The bandwidth of the phase shifter is around 26% within +/- 1 degrees errors over the frequency band from 8 to 12 GHz.