Interdigital, Band-Pass Filters

The filters discussed in this paper consist of arrays of TEM-mode transmission line resonators between parallel ground planes. Each resonator line is a quarter-wavelength long at mid-band and is short-circuited at one end and open-circuited at the other--the resonator elements being arranged in a parallel array with the positions of the short-circuited ends alternating. Figure 1 shows a strip-line interdigital filter with its upper ground plane removed.