Filters are a complex topic. I have designed them for over 20 years. The topic of symetery is interesting in that most are symeterical if looked at with the frequency scale in log format and if a "full bandwidth" approximation is used.The best I can suggest is to provide some references you can use to gain a better understanding of filters. "Handbook of Filter Synthesis" by Anatol I. Zverev 1967 This is great for the tables but does not provide the necessary ne-normilization equations. "Filtering in the Time and Frequency Domains" by Herman J. Blinchikoff 1976. This is an advanced text that will require some study. "The Analysis, Design, and Synthesis of Electrical Filters" by DeVerl S. Humpherys 1970. This is a graduate course in filter synthsis. "Electronic Filter Design Handbook" by Arthur B. Williams. This is an entry level book but is filled with errors so you almost need to know the material before using it. But it can provide some useful information. and last "comprehensive Filter Design" by Lee R Watkins 1997. This has a lot of useful information and most all of the de-normaiization equations as well as a host of graphs to assist in the design of filters. Good Luck!
Thanks for the education! I have observed for many years that filter pass-bands are not symetrical, but I had not had an adequate explanation until this one. So thanks for not only explaining the cause, but also describing a solution. Of course, after those series sections are added the design is not really a simple filter any more. BUT having a good explanation is certainly worthwhile. Thanks for the educational post!
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