Characterization and modeling of a wideband microstrip balun

The authors describe the characterization and modeling of a hybrid microwave balun with a wide frequency bandwidth from near DC to about 5 GHz. The modeling is carried out in the time domain by using the modified transient circuit analysis package (MTCAP) and the PSPICE package in the frequency domain for verification purposes. The phase-reversal transition region is shown to limit the balun´s bandwidth. The effect of the ground current due to phase reverse can be modeled using a high-impedance transmission line coupled with a negative signal line at the phase-reversal junction. The model obtained is in good agreement with experimental results.<>