Investigation of bandpass filters based on layered dielectric structures

Abstract

The designs of band-pass filters on multilayer dielectric structures consisting of half-wave resonators exclusively, as well as with quarterwave resonators at the edges of the considered structures are investigated. The principles of constructing devices with specified characteristics are described and the basic laws of the behavior of frequency-selective properties of multilayer structures on their design parameters are explained. It is shown for the first time that in multilayer bandpass filters on one-dimensional dielectric structures, the frequency responses remain unchanged when the steps of the characteristic impedance between adjacent layers of the structure are inverted. The boundaries of the realized characteristics of filters are determined using the existing set of modern materials widely used in radio engineering (1 ≤ ε ≤ 1000). It was found that the achievable values of relative passband in constructions consisting exclusively of half-wave layers ranged from 21% to 93%, while the most narrow-band filters can be realized with interface media having characteristics of Z0 ≈ 85 Ohm (ε ≈ 19.7) in the case of a forward step of the characteristic impedance at the edge interfaces of the structure and Z0 ≈ 53 Ohm (ε ≈ 50.4) – in the case of the reverse step (inversely proportional to the original). It is demonstrated that for the structures with the edge quarter-wave layers (all the inner layers are half-wave), other things being equal, the selective properties become better, but the relative passband can vary from only 45% to 115%, while the lower limit is achievable only in the case of air interface media (Z0 ≈ 377 Ohm, ε = 1).