Modeling the transition between a coaxial line and a flat rectangular waveguide

This paper presents theoretical and experimental investigations on the coupling between a coaxial line and a very flat dielectric filled waveguide with dimensions smaller than half of the free space wavelength. The transitions in two different frequency bands, X- and L-band, have been studied. A classic closed-form expression for the impedance of the mono-filament probe is evaluated from the knowledge of the complex power flowing into the rectangular waveguide supporting the dominant mode. For an optimal coupling, the structure and the dimensions of the mono-filament probe has been modified. The modifications depend on the operational frequency. The coupling shows a wide-band transition for both frequency bands