Dual-band metallic waveguide with low dielectric constant material

A metallic waveguide with dual in-line dielectric rods can propagate electromagnetic waves more than two times higher than the cutoff frequency region without higher modes. This type of waveguide, however, requires many rods with a high dielectric constant such as 29.5. Sintered alumina, with a dielectric constant around 9, may be more suitable for dielectric rods, as it is a popular material for use in microwave systems. Attenuation constants for alumina and for a high dielectric constant material were calculated using the finite-difference time-domain method and compared. Although the attenuation constant for alumina is higher than that of the high dielectric constant material due to its high loss tangent, it is not so high to make it practicable.