Robust Contactless Noncircular Choke Flange for Wideband Waveguide Applications

This paper describes the novel design concept of a wideband noncircular choke flange for connecting two contactless waveguide joints with the variable air gap. Resonant enhancement of transmission loss is observed in the experiment as well as the numerical simulation in Ansys HFSS software when a 2-D standing wave is excited in the narrow air gap. The shape of the choke groove is designed in such a way that ensures standing waves cannot be excited in the frequency band of interest, even considering possible linear and rotational misalignments between the connecting joints during practical operation, thereby making the design very robust. The eigenmode analysis is performed to decompose the mixed excitation mode into the fundamental and higher order modes, and for the case of misalignment, revealing why the electric field changes the direction of rotation above and below the resonant frequency. Experimental measurement results of the fabricated egg-choke flange showed that the transmission loss is less than 0.1 dB in the 2.5-GHz bandwidth from 8.5 to 11 GHz with possible misalignment which validates the design. Other choke shapes are possible following the same design methodology with different scaling parameters depending on the desired frequency band of the user application.