CHARACTERISTICS OF A TWO-RESONATOR COMB-TYPE MICROSTRIP ELEMENT WITH AN OPTIMAL LENGTH OF THE COUPLING REGION BETWEEN THE RESONATORS

Abstract

When designing microwave devices, an important role is played by the introduction of additional structural elements or parameters into the filter topology, the appropriate choice of which allows you to optimize the characteristics of the device according to a given criterion. The paper considers a method for expanding the barrier band of a comb-type microstrip filter by introducing a longitudinal displacement between the resonators. It is shown that a certain choice of the length of the coupling region between the resonators makes it possible to minimize or reduce to zero the coupling between them in the vicinity of the tripled average frequency of the main bandwidth, and thereby significantly suppress the parasitic attenuation dip in this frequency range. In the process of designing the filter, a synthesis method was used based on the transition from the filter to the corresponding 2n-pole, where n is the number of filter resonators. This approach allows us to consider the filter as a set of individual resonators connected to each other, and to introduce the concept of potential bandwidth, which can be easily determined by the characteristics of the 2n-pole and positioned in the desired frequency axis interval by an easily formalized algorithm for selecting the geometric dimensions of the device. The electrical characteristics of the 2n-pole used to synthesize the device within the baseband and at the stage of optimizing the device parameters in the vicinity of the tripled value of the baseband frequencies are the intrinsic conductivities of the resonators and the conductivities of the connection between them. The aim of the work is to study the effect of the length of the coupling region between the resonators of a two-resonator microstrip comb filter on its electrical characteristics. It is shown that the choice of the optimal value of the length of the coupling region between the resonators makes it possible to expand the barrier band of the filter at a level of minus 30-35 dB by more than two times due to the suppression of the parasitic bandwidth formed in the vicinity of the tripled average frequency of the main bandwidth. This positive effect, which consists in expanding the filter barrier band, is confirmed by the results of designing a comb filter on two offset resonators in the HFSS program.