Balanced Wideband Quasi-Schiffman Phase Shifters Based on Slotlines

This brief presents a quasi-design about balanced wideband Schiffman phase shifters based on slotlines, which can achieve phase shift with relatively small phase equiripple and high common mode (CM) rejection. The proposed balanced phase shifters are mainly composed of a microstrip/slotline transition structure and a C-section coupling slotline. C-section coupling slotline consisting of two long parallel coupling slotlines and two short parallel coupling slotline can achieve the phase shift function. The microstrip/slotline transition structure is employed as a balanced port, so that the differential mode (DM) response and CM one are independent of each other. Different from the traditional Schiffman phase shifter: two methods are used to compensate the different phase velocity between the odd and even modes. In order to decrease the DM transmission loss, sandwich structure is also employed in this design. To the best of authors' knowledge, the balanced wideband Schiffman phase shifter based on slotline may be the first ever reported. Finally, 45 degrees, 90 degrees and 180 degrees phase shifters with a central frequency at 2.37 GHz are achieved to verify the design method. The measured results agree well with the simulation.