Abstract-A circular waveguide loaded with dielectric and metal discs was chosen to evaluate its dispersion characteristics and dispersion shaping with change of structure parameters for wideband coalescence of beam-and waveguide-mode dispersion characteristics for wideband gyro-TWT performance.The azimuthally symmetric TE-mode analysis of the structure was carried out in field matching technique by considering the propagating wave in cylindrical free-space region having radius equal to the hole-radius of metal disc, and the stationary waves in free-space and dielectric regions between two consecutive metal discs. The dispersion relation and, in accordance, a computer code were developed. Further, the roots of the dispersion relation for various sets of the structure parameters were obtained using the developed computer code; the dispersion characteristics were plotted; and the dispersion shaping was projected for typically chosen TE 01 -, TE 02 -and TE 03 -modes. The analytical results were validated against those obtained for the conventional and earlier published structures, and also those obtained using commercially available simulation tool. Finally, a study on azimuthal electric field available over the radial coordinate was carried out to show the control of structure parameter on the gyrating electron beam position for the chosen operating mode of a dielectric and metal discs loaded gyro-TWT.

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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.

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In this paper, triple-band stacked microstrip patch antennas (MPAs) are presented with wide impedance bandwidth and suppressed cross-polarization level. Triangular and circular shaped slots are embedded in the patch of antenna. Slot-loaded microstrip patches are fed with meandered microstrip line supported by a semi-ground plane structure. Triangular shaped slot-loaded MPA shows triple resonance at frequencies 2.2, 4.45, and 5.3 GHz having bandwidth of 45.9, 19.23, and 15.67%, respectively. Circular shaped slot-loaded MPA also shows triple resonance at frequencies 2.2, 4.42, and 5.38 GHz having bandwidth of 50.24, 33.21, and 13.43%, respectively. Using circular slot in place of triangular; bandwidth of the first and the second band is improved by 4.34 and 13.98%, respectively. Both the proposed antennas show an omnidirectional radiation pattern at all three resonance frequencies in the xz-plane with almost 0 dBi gain. Both the proposed antennas are fabricated on a FR-4 epoxy substrate and show a minimum level of cross-polarization radiations.