Two-Resonator Microstrip Filters with Increased Single-Sided Frequency Selectivity

In this paper, we study the frequency properties of microstrip two-resonator structures that implement the characteristics of bandpass filters with increased one-sided frequency selectivity. It’s shown that these structures have a sufficient number of freedom degrees to fulfill the conditions for the parasitic passbands’ degeneration and the formation of a significant number of working attenuation poles, two to three times the number of resonators in the structure. These attributes provide a combination of low passband loss and increased frequency selectivity over a wide stopband up to and including the fifth harmonic. The noted features determine the possibility of these structures’ wide application as both independent compact filters and basic units as part of highly selective filters of a higher order. The paper also presents the results of electrodynamic 3D modeling of the proposed structures.