Transmission-line directional couplers for impedance transforming

Normalized scattering parameters of a two-port circuit terminated in arbitrary impedances are derived and design equations of directional couplers for impedance transforming are derived. To verify the design equations, a microstrip directional coupler is designed at a center frequency of 2GHz, fabricated on a substrate (/spl epsiv//sub r/=3.5,H= 30mil, tan/spl delta/= 0.04) and measured. The measured performance shows good agreement with the simulated one.