Then: Microwave Filter Design Techniques

Many papers have been written on the theoretical design of microwave filters and the methods for computing the theoretical constants of a particular filter are known.

The gap between the computation of the constants of the filter parameters and the fabrication and alignment of the filter to realize the required response is one that requires some attention since this is the stage which generally consumes much of the time in any development program. This paper will discuss a filter technique whish has been developed for the design of direct coupled microwave filters permitting the design engineer to build and align the filter so that the resulting response curve will essentially duplicate the theoretical performance curve.

A direct coupled filter consists of a number of waveguide cavities, each cavity being coupled to an adjacent cavity by an aperture or iris. The theoretical design of these filters is well known and design data for networks capable of realizing a Butterworth or maximally flat response and the Tchebyscheff or equal ripple response is available^1,2,3,4 A typical arrangement and associated low frequency equivalent circuit is shown in Figure 1.