Broadband Matching of Microstrip Differential Phase Shifters

Meanderline phase shifters in microstrip are badly matched (vswr ¿ 2), due to the difference in phase velocity of the odd and even mode of the coupled transmission lines. This is overcome by a stepped impedance design, allowing to realize e.g. a 90° phase shifter with a return loss better than 30 db across an octave bandwidth. Straightforward design equations are derived and confirmed by measurements on MIC´s in the frequency range 4 to 8 GHz and X-band.