Circuit engineering methods for increasing frequency selectivity of microstrip filters
based on half-wave co-directional hairpin resonators are studied, the principle of operation
which is based on the rational use of the effect of inequality of normal wave phase velocities.
It is shown that in these structures with N resonators, it is possible to form N + 1 operating
attenuation poles at finite frequencies without introducing additional electromagnetic couplings
between non-adjacent resonators. The conditions for splitting the operating attenuation poles in
compact multiply coupled structures are determined. The results of experimental studies of this
type of highly selective filter are presented.
Keywords: Attenuation pole, Coupled structures, Equivalent circuit, Elliptical characteristic, Frequency response, High-selective filter, Hairpin resonator, Lattice section, Strip resonator, Microwave range.
