Microwave waveguide-grating dielectric filters

Studies of resonance anomalies in waveguide gratings have demonstrated unique filtering capabilities of such structures. This new type of optical filter combines the principles of diffraction by periodic structures with waveguide theory and antireflection thin-film properties to yield filters with 100% reflectance at a desired wavelength. By appropriate choice of the multilayer waveguide-grating parameters, one can design narrowband or broadband reflection filters with arbitrarily low, symmetric sidebands extended over a large frequency range. Multilayer structures yielding high reflection off resonance can be used to design high efficiency transmission bandpass filters with similar features. The paper illustrates the characteristics of reflection and transmission bandpass filters in the microwave spectral region. Owing to the larger sizes of the gratings and the availability of materials with larger dielectric constants, there is increased flexibility in the design of microwave filters as compared to their optical counterparts.