Stripline bandpass filters with alternating coupling coefficients

Abstract

This article shows the possibility in principle to design stripline comb filters with alternating signs of the coupling coefficients. The new feature of the stepped-impedance resonators of the quarterwave type was established. They provide the opposite sings of the electromagnetic coupling with adjacent resonators. Such resonators are asymmetric relative to the vertical axes, which is drawn through their middle part. The stripline passband filters with alternating signs of coupling coefficients have attenuation poles that are located to the left and to the right of the passband. Those poles improve the selectivity of such filters. The articles provide the measured characteristics of the stripline comb filter of the forth order with alternating coupling, which has the central frequency of f₀ = 1835 MHz and the passband width of 90 MHz. The filter is constructed using a dielectric material with relative permittivity of ε_r = 92 and has the dimensions of 7.4×4.2×2 mm.