Junction Effects Reactance on X-Band and Dimensional Tolerance 3-Db Directional Couplers

Theoretical characteristics are presented for X-band 3-dB rat-race and branch-line couplers using gold microstrip lines with a semi-insulating GaAs dielectric. The rat-race configuration is shown to be less influenced by junction reactance and dimensional tolerances and has a greater bandwidth than the two-branch coupler. However, the rat-race coupler has the disadvantage that the output arms are not adjacent. Three-branch couplers are shown to have bandwidth comparable to the rat-race coupler but are much more sensitive to junction reactance and dimensional tolerances.