Modern filter design has evolved through the years from a subject known only to specialists in the field (because of the advanced mathematics involved) to a practical well-organized catalog of ready-to-use circuits available to anyone with a knowledge of eighth grade level math. In fact, an average individual with absolutely no prior practical filter design experience should be able to sit down, read this chapter, and within 30 minutes be able to design a practical high-pass, low-pass, bandpass, or bandstop filter to his specifications. It sounds simple and it is once a few basic rules are memorized.

The approach we will take in all of the designs in this chapter will be to make use of the myriad of normalized low-pass prototypes that are now available to the designer. The actual design procedure is, therefore, nothing more than determining your requirements and then finding a filter in a catalog that satisfies these requirements. Each normalized element value is then scaled to the frequency and impedance you desire, and then transformed to the type of response (bandpass, high-pass, bandstop) that you wish. With practice, the procedure becomes very simple and soon you will be defining and designing filters.

The concept of normalization may at first seem foreign to the person who is a newcomer to the field of filter design, and the idea of transforming a low-pass filter into one that will give one of the other three types of responses might seem absurd. The best advice I...