Sensitivity Analysis of Coupled Microstrip Directional Couplers

Sensitivities of the parameters (coupling, bandwith and impedance) of a coupled-line directional coupler with respect to even- and odd-mode impedances have been evaluated. These are used to determine the accuracy required from the closed-form expressions for even- and odd-mode impedances of microstriplines. Closed-form expressions satisfactory for a coupling coefficient greater than 0.3 are proposed and used for evaluating the effect of dimensional tolerances on the performance of microstrip directional couplers. This effect is significant when compared with effects of unequal phase velocities and dispersion.