Design of a wideband balun using parallel strips

A new wideband balun is presented. The designed balun has a symmetrical four-port structure with one port open-ended. It consists of a wideband impedance transformer and a broadband phase inverter. To design the wideband impedance transformer, an S-plane high-pass prototype has been exactly synthesized with third order Chebyshev response. A wideband parallel strip balun operating from 0.72 to 2.05 GHz is fabricated and tested to verify the design concept. The measured results match well with the design theory.