Figure 1

Cross-section of the annular waveguide with outer boundary which is a perfect electrical conductor (PEC). Here, the dielectric permittivities \(\varepsilon_{1} := \varepsilon_{1}(R_{\mathrm{WLR}},s)\), \(\varepsilon_{2} : = \varepsilon_{2}(R_{\mathrm{DGR}}, s)\) are dependent on the parameters \(R_{\mathrm{WLR}}, R_{\mathrm{DGR}}, s\) which are defined in Table 1.