Analysis and design of impedance transformed balun integrated microwave probe for differential circuit measurement

This paper presents an integrated broadband balun probe for differential circuit measurements. The balun consists of the two broadside coupled coplanar strips with a finite ground plane. A new analysis method for the Marchand balun is developed for optimizing design parameters. The design parameters are calculated from newly developed conformal mapping analytic expressions. This method verifies the serious effects of the ground plane width variation in a broadside coupled CPS. Final balun design shows a very wide bandwidth (20∼100GHz) with small phase difference (≪5°).