An Engineering Approach to Calculating and Optimizing the Parameters of a Non Radiating Half-Shielded Dielectric Waveguide

Abstract

The parameters of half-shielded dielectric waveguides optimized in terms of their frequency bandwidth are investigated as a supplement to the procedure for designing waveguide transitions. The half-shielded dielectric waveguide is a rectangular dielectric rod placed between two parallel metal plates. Such a waveguide is in its own way a "hybrid" of open and closed transmission lines. It simultaneously has the properties of both the types of transmission lines; these properties may exhibit themselves to a greater or lesser extent depending on the design. Under certain conditions, a so called non-radiating effect is observed in this waveguide, a phenomenon consisting in that the electromagnetic energy is held in the dielectric rod when it is bent or deformed (provided, however, that the plane symmetry is retained). The ratio of the distance between the metal plates to the dielectric rod width is called the rod form-factor. For a non-radiating mode, there exists a certain optimal form-factor, at which the maximum frequency bandwidth is reached. The frequency bandwidth as a function of the waveguide form-factor is presented. Dependences characterizing the optimum form factor (according to the largest frequency bandwidth criterion) versus the medium parameters are investigated, and empirical formulas for evaluating them are proposed. An engineering method is proposed for calculating the physical parameters of non-radiating dielectric waveguides, which is one of the stages in calculating waveguide transitions. Empirical formulas for estimating the dependence of optimal form-factor on the parameters of medium are investigated and proposed. Dependences of the optimal form-factor and the frequency bandwidth coefficient on the ratio of dielectric constants of the waveguide rod and external medium are presented. An engineering method for calculating the physical parameters of non-radiating half-shielded dielectric waveguides is suggested. It is found that the non-radiating dielectric waveguide's frequency ratio lies in the range from 24 to 30%. It is shown that materials with a dielectric constant higher than 5 are best suited for achieving the largest frequency bandwidth. A formula for approximating the dependence of the optimal form-factor on the rod dielectric constant in the range from 1.5 to 30 is proposed.