Bandpass filters for use in millimeter wave quasi-optical systems

Techniques are developed to model the behavior of grids of annular apertures and to analyze stacks of grids separated by layers of dielectric. The resonant properties of annular rings make them well suited for filter and oscillator circuits in the millimeter-wave region. Two-dimensional, periodic arrays of annular apertures in a metallic screen can be used as bandpass filters with 100% transmission, occurring when the wavelength is equal to the ring circumference. The shape and location of the passband are a function of the inner and outer ring radius and the period of the mesh. By stacking planar filters and using dielectric slabs, sharp filtering can be achieved. Narrow rings can have relatively high quality factors, making them particularly appropriate for the incorporation of active devices. A theory for designing bandpass filters with annular rings is presented, and compared with measurements in the range of 29-40 GHz.<>