SELECTIVE PROPERTIES OF TWO-RESONATOR STRUCTURES AND HIGHLY SELECTIVE FILTERS BASED ON THEM

An increase in the frequency selectivity of microstrip filters is traditionally achieved by forming transient response zeros at final frequencies. In this case, the specified requirements for the selectivity of filters are provided with a smaller number of resonators, and, consequently, lower loss es in the passband are achieved in more compact structures. Thus, the effectiveness of this approach to the synthesis of microstrip filters is determined by the number of transient response zeros that can potentially be formed in various structures. One way to form damping transient response zeros is to introduce additional cross-couplings between non-adjacent resonators. However, when synthesizing highly selective filters based on such widely used N-resonator structures, a limited number of transient response zeros equal to N-2 is formed. At the same time, two-resonator structures are known in which a much larger number of transient response zeros is formed, which is several times greater than the number of resonators in them. However, each of these structures has its own specific frequency-selective properties, which limits the scope of their wide application as universal links. The aim of this work is the synthesis of highly selective two-cavity structures with various types of frequency characteristics, which expands the scope of such structures. The frequency properties of microstrip two-resonator structures of a new type, which have broad functionality and increased frequency selectivity, are studied. It is shown that in multistage structures on two half-wave hairpin resonators, under certain conditions, a significant number of transient response zeros is formed, which is two to three times greater than the number of resonators in the filter, and parasitic transmission bands also degenerate. Depending on the ratio of the coefficients of electromagnetic interaction in different sections of the length of the coupled resonators, they acquire the properties of both single-band and multi-band bandpass filters, as well as low-pass filters. The noted features predetermine the possibility of wide application of these structures as both independent compact filters and basic units as part of higher-order filters with a significantly limited number of resonators. The results of electrodynamic 3D modeling and experimental studies of the proposed structures are presented, which are in good agreement.