Metamaterial-inspired waveguide filters with compact size and sharp skirt selectivity

Abstract

In this paper, a metamaterial-inspired miniaturization method for waveguide filter design is proposed. The transmission response and effective medium parameters of I-shaped resonator in metallic rectangular waveguide are first discussed. By embedding such an I-shaped resonator, a novel λ_g/2-type inverter is then proposed (λ_g: the guided wavelength). The large effective refraction index with low loss which appears below the resonant frequency of the I-shaped resonator is skillfully exploited, and then the size of λ_g/2-type inverter is greatly reduced with acceptable low insertion loss. The most negative permittivity of the I-shaped resonator at its resonant frequency produces an additional transmission zero which leads to sharp skirt selectivity in the upper side band. Using the novel λ_g/2-type inverter, two improved waveguide filters are further designed with good performances. One has an extremely compact size. The other has further improved selectivity. Two such filters are finally fabricated and the measured results agree well with the simulated ones.

Acknowledgments

This work was supported in part by the National Natural Science Foundation of China under Grant No. 60901022, in part by the Research Fund for the Doctoral Program of Higher Education under Grant No. 20090185120005, and in part by the Fundamental Research Funds for the Central Universities under Grant No. ZYGX2010J021.