Four- and Five-Resonator Microstrip Structures with Increased Frequency Selectivity

In this paper, the authors investigate the design features of compact high-selective microstrip filters based on structures with a significantly limited number of folded half-wave hairpin resonators. A significant number of the working attenuation poles, which is several times greater than the number of resonators in the filter, is formed in these structures with increased frequency selectivity under certain conditions. In this case, the order of this type filters transfer characteristic is determined in the passband by the number of resonators in the structure and in the stopband - by the number of working attenuation poles. This filter order feature provided a combination of low loss in the filter's passband and increased frequency selectivity over a wide stopband.