Separation of band-gap overlap in a coaxial Bragg structure operating in higher-order mode at Terahertz frequency

Abstract

Band-gap overlap always occurs when an overmoded coaxial Bragg structure operates in the Terahertz frequency spectrum, which may cause serious competition of undesired modes with the operating mode at the operating frequency. In the present paper it is revealed that band-gap overlap of modes can be efficiently separated by setting the phase difference between the outer- and inner-conductor corrugations to be π. Moreover, the residual side-lobes interaction of the involved modes in a coaxial Bragg structure can be entirely eliminated by applying Hamming-window distribution to both the outer-conductor and inner-rod corrugations. These peculiarities provide potential advantage in constructing a coaxial Bragg cavity with high quality factor for single higher-order-mode operation of a high-power free-electron maser in the Terahertz frequency range.