This article describes a synthesis method dedicated to the design of frequency-independent phase shifters (PSs). This innovative PS structure consists in a transmission line cascaded with a negative group delay (NGD) active circuit so that the absolute constant group delays generated by both of them are identical but of opposite signs. So, in principle, it exhibits a constant overall phase and a group delay close to zero. Broadband linear positive phase slopes are obtained through use of an NGD active circuit whose characteristics are recalled prior to the extraction of the PS synthesis relations. The design and simulations of a PS of compact size are reported. The experimental results confirm the expected frequency-independent transmission-phase value of 145° with an insertion gain of 2 dB over a 160% relative frequency band. At last, future prospects allowed by the specific properties of this PS are presented