Analysis of a Circular Waveguide Loaded With Dielectric and Metal Discs

Abstract

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.

Propagation Characteristics of a Variant of Disc-Loaded Circular Waveguide

“…The axial-periodicity in the interaction structure of a gyro-TWT promises the broadbanding through dispersion shaping that allows wideband coalescence between the beam-and waveguide-mode dispersion characteristics and, in turn, the broadband gain-frequency response [27][28][29][30][31][32][33][34][35][36][37]. Choe and Uhm [36] analyzed the infinitesimally thin disc-loaded circular waveguide ignoring the higher order stationaryand propagating-wave modes in the field matching technique and presented the dispersion shaping by changing the structure parameters.…”

“…The azimuthal periodicity in interaction structure may be seen, for example: in travelling-wave magnetrons [14] for π-mode operation, in gyrotrons [21][22][23][24] for mode rarefaction, in conventional helixTWTs [17] for broadbanding, in gyro-travelling wave tubes (gyroTWTs) [25,26] for higher interaction impedance and, in turn, for higher device-gain. The axial periodicity in interaction structure may be seen, for example, in conventional helix-TWT [17] for higher device-gain, in coupled-cavity TWT [17] for getting fundamentalmode backward-wave characteristics, and in gyro-TWT [27][28][29][30][31][32][33][34][35][36][37][38][39] for broadbanding.…”

“…Kesari et al [34] combined the two methods, metal and dielectric loadings, of dispersion shaping to propose an alternatively metal and dielectric discs-loaded circular waveguide with same [34] and with different [35] metal and dielectric disc-hole radii. The dispersion characteristics of a similar structure in absence and in presence of annular electron beam were also analyzed in [13] including the instability performance.…”

“…and even in the vacuum electronic devices, such as, linear/particle accelerators [11,12], backward-wave oscillators (BWOs) [13], magnetrons [14], coupledcavity and helix travelling-wave tubes (TWTs) [15][16][17][18][19], cyclotron masers [20,21], gyrotron sources [21][22][23][24] and amplifiers [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39], etc.. In these devices, one may see the periodic beam-wave interaction structures holding either azimuthal or axial periodicity [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]…”

A Novel Slotted Helix Slow-Wave Structure for Millimeter-Wave Traveling-Wave Tube

“…Millimeter-wave radiation sources with high power, wide-bandwidth, and high efficiency are attractive for many applications, such as high-date-rate communications, high-resolution radar, and space applications [1][2][3][4][5][6][7][8]. Helix TWT is one of the most important millimeterwave vacuum amplifiers due to its outstanding combined performances in bandwidth, power capacity, and electronic efficiency.…”