Multilayer thin film bandpass filter

Abstract From the Canadian patent

A novel design for producing band pass filters with essentially square shapes with little or no ripple in the passband zone. Filters are of the all-dielectric type consist of multiple cavities of band passes. Quarter wave thick layers of low index material separate all of the cavities from each other. Multiple half-waves may be added to the outer cavity quarter-wave stacks in particular. This invention provides the addition of half wave to some of the inner cavity stacks to remove ripple that would otherwise be present. Together these additional half wave layers added to the outer and inner cavities sharpen the transition from low transmission to high transmission without unduly adding …