Synthesis of Angular Bandpass Filters

Angular bandpass filters find application in advanced antenna feed systems for space applications as diplexers or as devices to reduce the effects of unwanted grating lobes. In this paper a new approach for the design of angular bandpass filters composed of cascaded metal-strip gratings is proposed. Contrary to the conventional "diffraction" approach where the resonating element is the grating itself, in the new approach the basic resonator is composed of two cascaded gratings. The distance between the two gratings represents the length of the resonator while the inter-resonator coupling can be adjusted by varying the widths of the metal strips. This alternative approach, called the "guided" approach, does not add significant complication to the structure but greatly enhances its electrical performances. It will be shown in fact that, following the approach we propose, the frequency behavior of the filter can be completely decoupled from its angular behavior in the design process thereby considerably increasing the design freedom.