High-Performance Microwave Heating Device for Tubular Loads Using a Quasi-Coaxial Structure

This letter presents a novel microwave heating method that utilizes tubular loads as a substitute for the inner conductor of a coaxial waveguide, thereby improving heating uniformity and energy coupling efficiency through the TEM mode. First, the effect of replacing the inner conductor of the coaxial waveguide with dielectric on microwave propagation was analyzed. It was found that the microwave still maintains the TEM mode when its dielectric constant exceeds 20. Second, a waveguide-to-coaxial transition is designed, utilizing probe coupling methods with a tapered structure, resulting in a 53% increase in return loss (-10 dB) bandwidth. Finally, a microwave heating device was designed based on this transition. Compared with common microwave ovens, the microwave energy conversion efficiency of this method exceeds 90% for tubular materials with dielectric constants from 20 to 70, and it exhibited higher uniformity. It can be applied to the continuous industrial production of tubular materials.