Compact digital phase shifter for active phased array antenna system

A compact digital phase shifter for an active phased array antenna system is made using a folded hybrid coupler. The theoretical analysis is given for the folded structure of a branch-line hybrid coupler. To validate its feasibility, the 4-bit digital phase shifter is designed using commercial simulators and implemented on a Teflon soft substrate (/spl epsiv//sub r/=2.17). Its circuit size is less than 3.5 cm /spl times/ 3.0 cm and it exhibits at least 50% size reduction as compared with the conventional configuration. Its experimental results are also presented.