Design of Dual Stopband Filters for Interference Suppression

When a broad band receiving system is co-located with high power emitters, receiver saturation is a major issue. Rejection of the local high power signals with minimal effect on the rest of the receiver passband is required. In this context, we present in this paper a method for providing two rejection bands (dual band rejection rather than dual passband) in a new and unique waveguide application. Cavity resonators are combined with resonant irises to provide a pair of relatively narrow rejection bands (at least 25 MHz wide) located within a wide passband, achieving at least 50 dB rejection while maintaining passband loss values to less than 1 dB. The filter structure that we propose is based on a simple modification of the traditional narrowband reject band filter. In this paper, we first describe the basic dual-band reject filter structure, and then we outline its design for a practical example. The paper is concluded with a comparison between simulations and measurements, showing very good agreement, thereby fully validating both the structure and the design procedure.