A Frequency Multiplexer/Demultiplexer for Dual Frequency Waveguide

Conventional rectangular metallic waveguides are seldom used at frequencies higher than twice the cutoff frequency because of higher mode propagation. Single-mode propagation is available for a metallic waveguide using two arrayed dielectric rods. Although coaxial-waveguide converters are generally used for the introduction of electromagnetic wave to metallic waveguides, impedances cannot be matched by only one converter, because of the narrow bandwidth. Accordingly a frequency multiplexer or demultiplexer that connects to two coaxial-waveguide converter is necessary for impedance matching in each frequency range. S-parameters for three waveguide ports were calculated using Ansoft's HFSS. Although the frequency width for the reflection coefficient of each port is not so wide, port isolation is above 20 dB from 14 GHz to 17.5 GHz between two output ports.