Scattering optimization synthesis of compact mode converters for waveguides

Discusses mode converters for overmoded waveguides. Various designs based on periodic PIBU perturbation have previously been demonstrated for conversion from say TE/sub om/ to TE/sub on/ modes in overmoded circular waveguides. These designs demonstrate high conversion efficiencies but their overall length is large compared to the radial dimensions of the waveguide. To resolve the problem of length and also to explore other possibilities, a different approach to the design of mode converters for waveguides is proposed, The method is based on a short forceful perturbation of the field rather than a periodic field disturbance caused by a grating like structure. For designing a mode converter, the problem is formulated as that of finding a scattering surface (formed by varying the transverse dimensions of the waveguide) which can scatter the incoming field in such a way as to convert it from one mode structure to the other. The shape of the required mode converter is found by optimizing the scattered power in the required output mode as a function of the surface profile of the scatterer.