Lumped-element isolator with lower symmetrical configuration of three windings

Ideal isolator conditions are derived using circuit analysis in a lumped-element isolator with three windings at angles of /spl theta/ and /spl phi/. The angle /spl theta/ can be arbitrary; however, /spl phi/ is restricted to lie on the bisector of cross-angle /spl theta/ or the supplementary angle of /spl theta/. We found that the isolator with /spl theta/=/spl phi/=60 [deg] behaves the same as the one with conventional structure with /spl theta/=/spl phi/=120 [deg]. However, the former has a 0/spl deg/ phase shift and the latter a 180/spl deg/ phase shift between the input and output. The theoretical prediction was experimentally confirmed with an 800-MHz-band isolator.