Annular shape interdigital filter with increased frequency selection design

The design of the interdigital bandpass filter of annular shape with increased frequency selectivity due to the convergence of the input and output lines and introduction of additional lines between them is suggested. This allows the amplitude-frequency characteristic of such a filter to be formed with attenuation poles on the edges of its bandpass, which significantly increases the steepness of its slopes. A model of such four-resonator interdigital filter is made and the results of its experimental investigations are given. They showed that the developed filter can be successfully used in measuring channels to determine the frequency of signals in modern microwave equipment for communication, radar and telecommunications.