Prediction of fabrication yield from low-pass prototype in a Butterworth direct-coupled cavity filter

Abstract-This work presents a methodology for the prediction of fabrication yield in band-pass Butterworth direct-coupled cavity filters. The sensitivity of the reflection parameter with respect to coupling coefficient variations is calculated in the low-pass prototype. From this value, the maximum degradation experienced by the reflection parameter in a worst-case scenario is given. A practical application of the existing relationship between the standard sensitivity and the stored energy in coupled resonator structures is also proposed, allowing to predict the fabrication yield directly from the group delay of the filter in Butterworth ladder networks. By way of illustration, a 6th order waveguide filter has been designed. The prediction of its fabrication yield has been obtained given a manufacturing tolerance, that has been applied to cavity lengths and/or widths. Results are compared with full wave simulations to validate the new methodology.