Foundations For Microwave Engineering

Analytic expressions for axial and radial electric fields in axisymmetric interaction gaps of klystrons and coupled cavity traveling wave tubes are derived. Introduction of the field shape parameter m results in both limiting cases of the field at the tunnel tips, that is, E equal to a constant and E approaching infinity as well as a continuous transition between these two limits. The transition represents actual, practical fields. This representation may be used to replace the somewhat arbitrary expressions being applied by various researchers to describe the fields.

Generalized representation of electric fields in interaction gaps of klystrons and traveling wave tubes with axial symmetry

Principles of Electron Tubes

The large-signal behavior of traveling wave tube amplifier for a linear beam dielectric loaded anisotropically conducting tape helix slow wave structure (SWS) is realized through a swift and reliab...

Large-signal field analysis of a linear beam travelling wave tube amplifier for the anisotropically conducting tape helix slow-wave structure supported by dielectric rods

Numerical and computational analysis of radiation characteristics of dielectric loaded helical antenna

The homogeneous boundary value problem existing in the electromagnetic wave propagation in a dielectric-loaded perfectly conducting tape helix with infinitesimal tape thickness is investigated in this study. The ill-posed boundary value problem is regularised using the mollification method. The homogeneous boundary value problem is solved for the dielectric loaded perfectly conducting tape helix taking into account the exact boundary conditions for the perfectly conducting dielectric loaded tape helix. The solved approximate dispersion equation takes the form of the solvability condition for an infinite system of linear homogeneous equations namely, the determinant of the infinite order coefficient matrix is zero. For the numerical computation of the dispersion equation, all the entries of the symmetrically truncated version of the coefficient matrix are estimated by summing an adequate number of the rapidly converging series for them. The tape-current distribution is estimated from the null-space vector of the truncated coefficient matrix corresponding to a specified root of the dispersion equation. The numerical results suggest that the propagation characteristic computed by the anisotropically conducting model (that neglects the component of the tape-current density perpendicular to the winding direction) is only an abstinent approximation to consider for moderately wide tapes.

Propagation of electromagnetic waves guided by perfectly conducting model of a tape helix supported by dielectric rods

The practically important case of dielectric loaded tape helix enclosed in a perfectly conducting coaxial conductor is analysed in this paper. The dispersion equation for the infinitesimally thin and anisotropically conducting tape is derived from an exact solution of a homogeneous boundary value problem for Maxwell's equation. The boundary value problem is solved to yield the dispersion equation which takes the form of the solvability condition viz., the determinant of the infinite-order coefficient matrix is zero. For the numerical computation of the approximate dispersion characteristics, all the entries of the symmetrically truncated version of the coefficient matrix are estimated by summing an adequate number of the rapidly converging series for them. The numerical computation of dispersion characteristics and phase speed variations for different values of b/a (outer conductor to inner helix radius) and effective dielectric permittivity is presented.

Wave propagation characteristics in anisotropically conducting dielectric loaded tape helix slow wave structures

This article presents the design and analysis of a staggered double-vane (SDV) slow-wave structure (SWS) for $W$ -band amplifier, with 20-dB gain and a very high bandwidth (~25%). The use of dual Bragg reflector at either end of the interaction structure increases the impedance matching and the radio frequency (RF) coupling efficiency at the input and output ports, thereby reducing the RF leakage at the electron gun and collector ends, from 15% to 25% to less than 0.6%. The attenuator section is simple to fabricate and optimally designed in order to provide an effective isolation (>20 dB) between the input RF signal in the input section and the RF signal reflected from the output section. The dispersion analysis, the transmission analysis of each section, and the beam–wave interactions were simulated using the Dassault system’s computer simulation technology (CST) eigenmode solver, time-domain solver, and the particle-in-cell (PIC) solver, respectively. The proposed design of the SDV SWS conclusively provides an enormous bandwidth of ~25 GHz with 20-dB gain for $W$ -band amplifier, when compared to its solid-state counterparts and earlier reported work as per the author’s knowledge.

Design and Analysis of a Wideband Staggered Double-Vane Slow-Wave Structure for W -Band Amplifier

A W Band staggered double vane (SDV) loaded traveling wave tube amplifier (TWTA) with two sections separated by a lossy dielectric loaded rectangular wave guide is studied in this paper. The dispersion characteristics and transient analysis of the slow wave structure are analyzed in Computer Simulation Technology Microwave studio (CST MWS) and High Frequency Software Simulator (HFSS). In this amplifier, we propose to use Bragg reflectors on both sides of the slow wave structure (SWS), at the windows for the sheet beam at the electron gun and collector ends; this increases the impedance bandwidth of the RF structure. The attenuator section is comprised of a rectangular waveguide loaded on either side with single lossy dielectric material spanning over 5.5 pitches. The loss profile of the attenuator and loss magnitude is optimized to provide a 20dB loss in separating the input and output sections. A bandwidth of 15GHz ranging from 90-105GHz is obtained through the analysis. In the PIC simulations, a sheet beam of 50mA current is fed with an operating voltage of 18.3kV. The TWTA yields 20dB gain in the 90-105GHz range.

Richards Joe Stanislaus

Papers

Propagation of electromagnetic waves guided by perfectly conducting model of a tape helix supported by dielectric rods

Large-signal field analysis of a linear beam travelling wave tube amplifier for the anisotropically conducting tape helix slow-wave structure supported by dielectric rods

Wave propagation characteristics in anisotropically conducting dielectric loaded tape helix slow wave structures

Design and Analysis of a Wideband Staggered Double-Vane Slow-Wave Structure for W -Band Amplifier

Investigation of a Sheet Beam RF Structure with Bragg Reflector for W band Amplifier