Effective graded-index guides for millimetre-wave applications

A novel dielectric waveguide that simulates optical graded index fibre is proposed for millimetre-wave applications. It is shown that a gradually varying refractive index across the guide can result in a well confined, single-mode propagation even in a guide several wavelengths wide. The desired index profile is achieved by varying the thickness or height of the waveguide. The effective-dielectric-parameter concept is introduced and used in generating the thickness profile which is approximated by a roof-top. Experimental results for a trial guide are presented and discussed together with the relative merits of this guide.