Removal of beam squint in series fed array antennas using abnormal group delay phase shifters

Phase shifting networks are ubiquitous in microwave devices and applications such as antenna feed networks where precise phase shifters are necessary for radiation pattern synthesis. Ideally, a phase shifter must provide low insertion loss, good matching, and achieve the desired phase shift over the required bandwidth. For a phase shifter with an approximately linear phase response, the phase bandwidth – the frequency range over which the phase error is within a given tolerance – is inversely proportional to the group delay [1]. Therefore, a phase shifter optimized for maximal phase bandwidth should ideally exhibit zero group delay. To achieve some of the above goals designers often periodically load a matched host transmission line (TL) with lumped elements to synthesize new dispersive properties [2–3]. For example, a microstrip TL is loaded with surface-mount components to construct 2-port networks exhibiting negative group delay (NGD) [2] and negative phase delay [3].