Foundations For Microwave Engineering

This paper presents a comprehensive theory of the cyclotron resonance maser (CRM) interaction in a circular waveguide. The kinetic theory is used to derive the dispersion relationships for both TE and TM modes. The TE mode case has been investigated by several authors, but there has been comparatively little work on the TM mode case. However, the TM mode interaction competes effectively with the TE mode interaction at relativistic electron energies. The conditions for maximum temporal and spatial growth rates are shown. The TM mode growth rates are found to vanish when the RF wave group velocity equals the beam axial velocity (‘grazing incidence’). The single particle theory is used to derive a compact set of self-consistent non-linear equations for the TE and TM mode interactions. These equations are particularly appropriate for the cyclotron auto-resonance maser (CARM) regime but applicability extends to other regimes as well. The conditions for optimum efficiency are investigated for oscillator and amp...

Linear and nonlinear theory of the Doppler-shifted cyclotron resonance maser based on TE and TM waveguide modes

We present the theory of a new amplification regime in traveling wave tubes (TWTs) composed of a slow wave periodic structure that supports multiple electromagnetic modes that can all be synchronized with the electron beam. The interaction between the multimodal slow wave structure and the electron beam is quantified using a multi-transmission line (MTL) approach based on a generalized Pierce model and transfer matrix analysis, leading to the identification of modes with complex Bloch wavenumber. In particular, we address a new possible operation condition for TWTs based on the supersynchronism between an electron beam and four modes exhibiting a degeneracy condition near a band edge of the periodic slow wave MTL. We show a phenomenological change in the band structure of a periodic MTL, where we observe at least two growing modal cooperating solutions as opposed to a uniform MTL, interacting with an electron beam where there is rigorously only one growing modal solution. We discuss the advantage of using such a degeneracy condition in TWTs that leads to larger gain conditions in amplifier regimes and also to very low starting beam current in high-power oscillators.

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Theory and New Amplification Regime in Periodic Multimodal Slow Wave Structures With Degeneracy Interacting With an Electron Beam

In this paper, we describe the design and experimental results from the rebuild of a 250 GHz gyrotron used for Dynamic Nuclear Polarization enhanced Nuclear Magnetic Resonance spectroscopy on a 380 MHz spectrometer. Tuning bandwidth of approximately 2 GHz is easily achieved at a fixed magnetic field of 9.24 T and a beam current of 95 mA producing an average output power of >10 W over the entire tuning band. This tube incorporates a double disk output sapphire window in order to maximize the transmission at 250.58 GHz. DNP Signal enhancement of >125 is achieved on a 13C-Urea sample using this gyrotron.

Continuously Tunable 250 GHz Gyrotron with a Double Disk Window for DNP-NMR Spectroscopy

The effect of broadening the bandwidth with a dielectric load in a cylindrical gyrotron is investigated for a hollow electron beam. The linear dispersion relation for the azimuthally symmetric, transverse electric (TE) modes is obtained by the method of the wave impedance matching. It is found that the TE perturbations exhibit three unstable modes characterized by their phase velocities vph : one fast wave, the long wavelength mode (LWM, vph ≳c), and two slow waves, the intermediate (IWM, c≳vph ≳ce−1/2) and the short (SWM, vph <ce−1/2) wavelength modes. The optimum conditions for the wide band operation are obtained individually for each mode. Although the bandwidth in excess of 40% is possible for the slow waves (IWM, SWM) at a small axial momentum spread, it decreases rapidly as the spread increases. On the other hand, the LWM yields approximately 10% of the bandwidth insensitive to the spread. It is also shown that for a small spread (<5%), the slow wave (IWM) is preferable for the wide band operation,...

Analysis of the wide band gyrotron amplifier in a dielectric loaded waveguide

SUNRAY-1D and 2.5D codes have been developed for multi-signal large signal analysis of a complete helix TWT. 3rd, 5th and higher order Intermodulation components including higher-order harmonics can be simulated accurately both for high electronic efficiency, narrow band communication TWTs and for octave bandwidth EW TWTs.

Simulation of inter-modulation components using SUNRAY code for large-signal analysis of a TWT

A general analytical approach was proposed to estimate the ohmic quality factor of circumferentially corrugated cavities having a finite-single-valued and continuous radius-profile in circular symmetry within the boundary of its length. In the present paper, two field profiles, namely, the sinusoidal and the Gaussian one, and four radius profiles, namely, the sinusoidal, the cosinusoidal, the triangular-sinusoidal and the triangular-cosinusoidal, of the cavity were considered and the results were presented in order to demonstrate the helpfulness of the proposed approach. Out of the eight cavity versions considered, the minimum and the maximum ohmic quality factors were obtained for the cavity with sinusoidal field profile and triangular-sin radius profile and for the cavities with Gaussian field profile with sinusoidal and cosinusoidal radius profiles. It has been found that for higher values of the cavity-length to corrugation-period ratio (≥3), the ohmic quality factor performances of the cavities in sinusoidal and cosinusoidal radius profiles overlap.

Analysis of Ohmic Quality Factor of Circumferentially Corrugated Circular Cavities

The short-length TE6,2-to-Gaussian mode launcher for a millimeter-wave transverse output gyrotron was designed and simulated using two different software tools, namely Launcher Optimization...

Simulation of TE6,2-to-Gaussian mode launcher for a millimeter-wave gyrotron

In [1] , the first name of the third author in the byline under the title of the paper [1, p. 3257] as well as in the biography of the third author [1, p. 3261] should read “Rengaswamy” instead of “Ramaswamy.”

Correction to “Boron Nitride and Sapphire Windows for 95-GHz Gaussian RF Beam”

A simple and volume efficient circular antenna-array design with a low profile programmable beam rotation mechanism was presented. The proper selections of the rotation vector and the excitation coefficients of rectangular array-elements were made for rotation of the beam. The proposed rotation mechanism was capable to rotate the radiation pattern at any desired speed and to transmit in any desired direction, and the design included the ease of construction. Although simulating the radiation pattern using FEKO EM simulator, two basic functions, the power splitter and the introduction of phase difference, were included in feed network of microstrip circuit to divide the power and then individually feeding the each patch after introducing the desired phase difference.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1759078714000312

Vishal Kesari

Papers

Simulation of inter-modulation components using SUNRAY code for large-signal analysis of a TWT

Analysis of Ohmic Quality Factor of Circumferentially Corrugated Circular Cavities

Simulation of TE6,2-to-Gaussian mode launcher for a millimeter-wave gyrotron

Correction to “Boron Nitride and Sapphire Windows for 95-GHz Gaussian RF Beam”

Beam-steering in a three-element circular antenna-array