Lumped‐Element Filters

This chapter provides an introduction to the theory, design procedure and practical construction of radio frequency (RF) filters based on lumped elements, inductors and capacitors. To start to understand the complexities of filter theory, it is necessary to briefly study transfer functions and Bode plots. The chapter describes three of the most common filter types for approximating the ideal filter characteristics, namely the Butterworth, Chebyshev, and Elliptic filters. The Butterworth filter can only give a steeper transition from passband to stopband by increasing the order of the filter. The elliptic filter exhibit sequi-ripple behaviour in both the passband and the stop band. The characteristic behaviour provides a more rapid transition from passband to stopband than does the Chebyshev or Butterworth filter, but at the expense of a finite attenuation level in the stopband. Zeros are placed in the stopband in order to maintain sufficient stopband attenuation.