Double-channeled omnidirectional filtering properties of the sandwich structures composed of single-negative materialsL. W. Zhang, G. Q. Du, J. P. Xu, Z. G. Wang and Y. W. ZhangEur. Phys. J. Appl. Phys., 47 1 (2009) 10501DOI: https://doi.org/10.1051/epjap/2009069