Harmonic suppression by leaky-wall waveguide filters

This paper discusses a particular type of nonreflecting waveguide filter in which the upper stop band is quite broad, typically extending three, four or more times the pass band center frequency. Because of its wide stop band range, this filter is useful for suppression of harmonic frequencies. This filter has been called the leaky-wall type because filtering action occurs by mounting an array of terminated secondary waveguides, acting as high pass absorbers, on a primary waveguide transmission line. The secondary waveguides are coupled to the primary guide by large apertures, properly dimensioned and oriented so that coupling may occur to the many higher order modes of propagation in the primary guide. The design of these apertures (i.e., their size, orientation and number) to achieve a desired stop band insertion loss as a function of frequency at least for the lower order modes is presented in this paper by a series of empircal curves. In addition, the techniques used to evaluate filter performance for a high power capacity S-band experimental model filter are presented.