Absorbing waveguides absorption coefficient

Concerning the absorption of evanescent waves, a 50-mm circular parallel-plate metallic waveguide whose TMi mode has a cutoff at 3 GHz is explored. For a wideband attenuation, the PML of [26] is selected. All implementations are performed with operators (3.42) optimized for k = 1.437. Various setups are constructed and their reflection coefficient is shown in Figure 7.6. Observe that all absorbers display a promising annihilation of evanescent waves below the cutoff frequency, while HO counterparts attain a considerable decrease of PML depths for specific reflection coefficient values. 

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