Low Ripple Notch Filter Designs Using Apodized Thickness Modulation

How to make a low-ripple notch filters—a band-stop filter—by reducing side lobes with apodized process.


An apodized discrete layer thickness design method for notch filters is presented. The method produces error tolerant designs with low ripple in the pass band regions without any additional numerical optimization. Sample designs are presented.

Multiple approaches have been used in the past for producing notch filters (also called minus filters). The two main approaches can be grouped into rugate and discreet layer designs. Although narrow stop band designs can be generated both as rugate as well as using discrete layers, an advantage of rugate designs is that the ripple (sidelobes) in the transmission regions can be minimized by applying an apodization function to the index amplitude variation. The method presented in this paper, combines the relative ease of manufacturing of discrete layer designs with the natural low ripple of an apodized graded index design.

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