Balance measurements in double-Y baluns

Amplitude and phase balances in a double-Y balun, which transforms a coplanar waveguide with finite ground plane (CPW/sub FGP/) into a coplanar line (CPS), are investigated theoretically and experimentally. Measured results are presented for two baluns with different lengths of open- and short-circuited stubs. The balun with longer stubs demonstrated better amplitude balance. In the frequency range 3 to 14 GHz the measured amplitude balance is better than 1 dB and the phase balance is better than 8/spl deg/. At the frequencies where resonances of the parasitic even mode appear, the balun has poor characteristics.