ALLPASS MEANDER LINES FOR WIDEBAND FIXED PHASE SHIFTERS

It is shown that allpass meander lines can be used in constructing wideband fixed phase shifters. Theoretically the Schiffman phase shifter is superior, but it requires very tight coupling for wideband performance. The paper shows that the meander line is useful in practice and that the tight coupling necessary for the Schiffman phase shifter can be avoided. Meander lines of the 3rd and 4th orders are analyzed and a general equivalent circuit for a symmetric even order meander line is presented. It is shown that a wideband fixed phase shifter can be obtained by using a meander line phase shifter in cascade with Schiffman sections. This new technique gives a wider bandwidth than the usual technique, without increasing the required coupling. Wideband 90 degree phases shifters have been used experimentally in the construction of wideband attenuators in the frequency range of 2 - 18 GHz. As an example a 3rd order meander line was used in a 2 - 7. 2 GHz PIN-diode attenuator with a VSWR better than 1. 85 for all attenuation settings.