Propagation Characteristics of a Variant of Disc-Loaded Circular Waveguide

Abstract

Abstract-The shaping of dispersion characteristics in a variant of disc-loaded circular waveguide was studied through electromagnetic analysis for assessing the structure for wideband coalescence of the beam-and waveguide-mode dispersion characteristics that entails the wideband gyro-travelling-wave tube (gyro-TWT) performance. In this variant of disc-loaded circular waveguide, the alternate dischole radii were varying, however, the structure was periodic. The structure periodicity coupled with Floquet's theorem and fieldmatching technique resulted into the dispersion relation of the infinitely long structure. A numerical code was developed to solve the dispersion relation, and the dispersion characteristics of the structure were analyzed for the azimuthally symmetric TE-modes. The effects of structure parameters were studied for getting a straight-line portion of the dispersion characteristics over a wide frequency range. The dispersion shaping was projected for typically chosen TE 01 -mode. The results were validated against those obtained for the conventional and un-conventional known structures and those obtained using commercially available simulation tool. The variation of azimuthal electric field intensity over the radial coordinate was also studied to examine the control of structure parameter for maxima-position, where the gyrating electron beam would be positioned for optimum beamwave interaction in a gyro-TWT.

Metal- and Dielectric-Loaded Waveguide: An Artificial Material for Tailoring the Waveguide Propagation Characteristics

“…In this model (model-3) a circular metallic waveguide of inner radius r W is considered in which annular disc of thickness T, inner radius r D and outer radius r W Interwoven disc-loaded circular waveguides [2,9,14,15]. Circular waveguide loaded with metal vanes [16][17][18].…”

“…This model (model-4) differs from the conventional disc-loaded circular waveguide due to different additional disc included in between two identical consecutive discs of conventional disc-loaded circular waveguide [2,9,14,15]. Thus, this model is considered with a circular metallic waveguide of inner radius r W in which annular disc of thickness T, inner radius r D and outer radius r W are arranged periodically with periodicity L. In addition, another annular disc of thickness T BH , inner radius r BH and outer radius r W are also arranged periodically with periodicity L such that the disc of thickness T BH is placed in middle of two identical consecutive discs of thickness T. The structure is known as the interwoven-discloaded circular waveguide.…”

“…Model-4: The boundary conditions (24) and (25) are also true for the model-4 ( Figure 5) at the interface, r ¼ r D , between the regions I and II. The additional boundary conditions at the interface, r ¼ r BH , between the regions II and III may be written as [2,9,14,15]:…”

“…The boundary conditions (26) and (27) state the continuity of the axial component of magnetic and the azimuthal component of electric field intensities at the interface, r ¼ r BH , between the regions II and III, and the null azimuthal component of electric field intensity at the disc hole metallic surface ( Figure 5) [2,9,14,15].…”

“…disc-thickness ( Figure 19) of bigger-hole-disc of the interwoven-disc-loaded circular waveguide are, respectively, the most and the least sensitive parameter for controlling the passband as well as shape of the dispersion characteristics [14,15].…”