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The complex dielectric permittivity of electrically lossy AlN-SiC composites has been measured over the 26.5-40 GHz frequency range (Ka band), at temperatures from -180 to 200 °C. The dielectric permittivity is found to be strongly sensitive to temperature. Additional broadband, room-temperature dielectric measurements indicate that the Ka-band response is situated on the high-frequency tail of a broad Maxwell-Wagner relaxation. Analysis of the temperature-dependent losses at 30 GHz in a composite containing 20% SiC by weight, using an effective cluster model, indicates the existence of two conduction processes within the SiC, with activation energies of 0.0064 and 0.095 eV. The low-energy process is consistent with a hopping conductivity and the higher-energy process is attributed to a nitrogen donor ionization. [ABSTRACT FROM AUTHOR]

In nearly any application of a microwave tube, noise characteristics are important figures of merit. This paper reviews and presents new results of recent studies of such noise. The areas discussed are ion noise in linear beam tubes, one of the oldest studied noise phenomena, and electron noise in gyroklystrons, one of the newest areas of interest. [ABSTRACT FROM AUTHOR]

In this article, the optimization of gyroklystron efficiency is investigated by employing a two–step procedure. As a first step, the prebuncher is analyzed using a small signal approximation, since the cavity(ies) here serve mainly to modulate the velocities of the electrons slightly, which will be bunched in the field-free drift section(s). It is found that the electrons entering the energy extraction cavity can be characterized entirely by only two dimensionless parameters: a bunching parameter q and a relative phase ψ. The numerical simulation of the extraction cavity, based on the nonlinear pendulum equations describing the interaction between the electrons and the rf field, supplemented by the initial conditions specified by q and ψ, constitutes the second step. The final result of this two-step analysis is the efficiency, η⊥,opt optimized with respect to q, ψ, and the magnetic detuning parameter Δ. This efficiency depends only on the normalized cavity length μ and the normalized rf field F of the energy extraction section. The efficiency as well as the conditions required to attain this optimum (qopt,Δopt, and qopt) are presented as contour plots on the (F,μ) plane and can be used efficiently to design gyroklystrons of any frequency and output power. [ABSTRACT FROM AUTHOR]

The nonlinear efficiency for a gyrotron oscillator operating at harmonics of the cyclotron frequency has been calculated and is presented as a function of generalized parameters for the second through fifth harmonics. The numerical results are valid for a wide range of operating conditions, including voltage, current, beam radius, cavity dimensions, and operating mode. Relatively high efficiencies are found even at high harmonics; the maximum transverse efficiencies for harmonics 2, 3, 4, and 5 are 0.72, 0.57, 0.45, and 0.36, respectively. The calculation of the efficiency in terms of generalized parameters allows the straightforward design and optimization of harmonic gyrotrons. The influence of the axial profile of the rf field in the gyrotron cavity on the efficiency is also investigated. Improved efficiency can be achieved with asymmetric field profiles. The implications of these results for the generation of millimeter and submillimeter wave radiation by harmonic emission are discussed. [ABSTRACT FROM AUTHOR]

A technique for realising nonlinear functions of order a 5 using cascaded third-order nonlinear functions is described. The technique can be used to efficiently generate higher-order nonlinearities for predistortion linearisation applications. The use of two cascaded third-order functions is experimentally demonstrated to be comparable to a fifth-order implementation in performance. [ABSTRACT FROM AUTHOR]

Two important new results are presented from a study of second harmonic (2ωc) emission from a pulsed gyrotron designed for fundamental (ωc) emission of 200 kW at 28 GHz in the TE021 mode. Simultaneous output at ω1≊ωc and ω2≊2ωc, with the condition ω2=2ω1 applying as ω1 was varied, has been observed for the first time. Strong, single mode 2ωc emission (80 kW at 50 GHz) is also observed, and such emission is shown to be characteristic of gyrotrons designed for high-power emission at the fundamental. [ABSTRACT FROM AUTHOR]

Studies of a cyclotron autoresonance maser are presented. The measurements are carried out at a frequency of 35 GHz using a mildly relativistic electron beam (1.5 MeV, 260 A) generated by a field emission electron gun followed by an emittance selector that removes the outer, hot electrons. Perpendicular energy is imparted to the electrons by means of a bifilar helical wiggler. Measurements give a small signal gain of 90 dB/m and a saturated power output of 10 MW. The corresponding electronic efficiency is 3%. Computer simulations are also presented. [ABSTRACT FROM AUTHOR]