volume | PIER Journals

Abstract

The dispersion equation for a rectangular tape helix with four rectangular dielectric support rods has been deduced using precise boundary conditions employing field restricting functions. The dispersion equation is a much simplified conjoint expression obtained for axial and transverse directions derived by solving an infinite set of linear homogeneous simultaneous equations, represented as an infinite order matrix whose determinant is zero. Dispersion characteristics plotted from the simplified dispersion equation consist of the dominant and additional higher-order modes similar to an open rectangular slow wave structure (SWS), but with the existence of β⁰a(k⁰a) roots everywhere without the limitations of the forbidden region boundary. The phase velocity curves obtained for the corresponding mode of the dispersion characteristics exhibit comparable behavior to the free-space rectangular helix SWS, especially in the third ``allowed'' region, which offers a wider beam-wave interaction region with phase speed equivalent to the speed of light at higher operating frequencies. The numerically computed dispersion curves and their corresponding phase velocities were plotted. Similar dimensional variations of the structure with discrete support rods were simulated using three-dimensional simulation software. The dispersion characteristics obtained from the simplified dispersion equation along with the dimensional variation of the dielectric-loaded rectangular tape helix SWS determine the capability and limitations of such minuscule traveling wave tubes(TWTs) as planar TWTs suitable for fabrication using micro-machining techniques.

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Dr. Naveen Babu

Dr. Nameesha Chauhan