Postscript to Two Papers on Waffle-Iron Filters(Correspondence)

Waffle-iron filters are waveguide "low-pass" filters, that is, they have a wide stop band above their pass band. They are useful for both low-power and high-power applications. A brief history of the development of this filter at Stanford Research Institute is given by Young and Schiffman. A new design principle which makes it possible to extend the pass band from, (typically) about 10 percent to about 40 per cent is also described; the pass band of that filter covers almost the whole of the recommended waveguide band, while its stop band extends from the second to the fourth harmonic, inclusive.