A microwave filter is a two-port component usually employed when there is a need to control the frequency response at any given point in a microwave system. They provide transmission at certain frequencies, which are known as the passband frequencies, and attenuation at other frequencies, which are referred to as the stopband frequencies. The frequencies outside the passband are attenuated or reflected. Microwave filter is often named after the polynomial used to form its transfer function (i.e., Chebyshev, Butterworth [or maximally flat], Elliptical, etc.). The filter can be further sub-divided into four categorises (i.e., lowpass, highpass, bandstop, and bandpass filters) according to its frequency responses. This chapter gives a detailed discussion on filter classification and transfer function. It also covers the analysis, design, and implementation of a test microwave filter using the 21st century SIW transmission line. The simulation and measurement results of the test filter is also presented, compared, and discussed.
