Converting baluns into broad-band impedance-transforming 180° hybrids

A technique for converting baluns into 180° hybrids by adding an in-phase power splitter is presented in this paper. Incorporating the broad-band antiphase and in-phase power splitting characteristics of the balun and power splitter results in a 180° hybrid with broad-band characteristics. This technique also provides a means of achieving perfect matching and output isolation for three-port lossless baluns. Applying this technique to a Marchand balun will result in a broad-band impedance-transforming 180° hybrid. Simple design equations based on the scattering matrix are presented. These theoretical results are validated by an experimental 180° hybrid using a coupled line Marchand balun. It achieves amplitude balance of 0.5 dB and phase balance of less than 5° from 1.2 to 3.2 GHz.