Theoretical investigation of dielectric-loaded waveguides for millimeter wave generation

Charges traveling inside or in the vicinity of dielectric media can generate radiation ranging from the microwave spectrum to visible light. The effects are known as Cerenkov radiation (CR) for constant dielectric medium, and transition radiation (TR) for alternating dielectric media. When the dielectric is constructed as a waveguide with a vacuum tunnel built inside for an electron beam to travel, the effects can be utilized for the generation of coherent millimeter waves. A device based on CR, called the Cerenkov maser, has been reported to generate radiation up to 150 GHz from an unbunched beam, and therefore it functions as an oscillator. Although the device has the drawback of having a very high threshold for the beam energy, it offers high power loading and simplicity for theoretical analysis. In this work we present an analysis based on field theory in order to calculate the gain and spectrum of the device and discuss key parameters including interaction length, off-resonant frequency, filling factor, etc. for optimization.