Small-signal gain calculations for electrostatically focused klystrons

The small-signal gain of an electrostatically focused klystron (ESFK) will be different from that of a conventional klystron because the drift tube is not dc field free and the RF bunching process is altered. A method for calculating the small-signal gain of an ESFK, based on a space-charge wave analysis of the lens cell, is presented. Calculated and measured values of small-signal gain for several different ESFK's are given.     

A Medium Power Electrostatically Focused Multiple-Beam Klystron

This paper presents data on a new device, a 7-beam, electrostatically focused klystron oscillator/amplifier with planned output of 2-kW continuous wave (CW) at 5.8 GHz for an RF-excited ion thruster. An abridged presentation of this paper was given at the International Vacuum Electronics Conference/International Vacuum Electron Sources Conference (IVEC/IVESC) 2006 Conference in Monterey, CA. Advantages over conventional magnetic focusing are discussed. A tube was constructed that exhibited expected performance. It produced about 500 W with three beams at saturation and was operated as both an oscillator and an amplifier. DC beam transmission was 99% but degraded rapidly at saturation. We discuss ways to mitigate this problem. Cavity gaps were used as focus lenses by applying a dc voltage across them, and this improved overall beam focusing. A technique for splitting cavities without lowering Q is presented. An unconventional construction technology was employed and is described.     

A Barkhausen-Kurz oscillator at centimeter wavelengths

This paper describes a new device for the generation of high-frequency oscillations in the centimeter wavelength region with high efficiency and low starting currents. The tube is fundamentally a Barkhausen-Kurz oscillator [1] utilizing a resonant cavity and a magnetically focused electron beam, but with no accelerating grids. The important features of this tube are the use of a parabolic potential distribution to utilize multiple transit electron motion, and the use of the magnetic field to control coupling between the electron stream and the resonator field and to reduce to negligible value the current intercepted at the resonator gap. A preliminary theory of the electronic energy interchange of this oscillator is provided, and the background theory of the oscillator design is discussed. Both X-band and K-band tubes have been tested. In the X-band tube, a maximum output power of 1.8 watts and a maximum efficiency of 13.5 per cent were obtained. At K band, the maximum power output was 430 milliwatts, and the maximum efficiency was 12.2 per cent. Starting currents belaw 0.1 ma have been observed at X band.     

Sinusoidal and digital high-speed modulation of p-type substrate mass-transported diode lasers

The modulation characteristics of GaInAsP diode lasers grown onp-type substrates have been studied on devices in which the parasitic bonding pads have been eliminated. The lasers have thresholds as low as 4.5 mA. The small-signal sinusoidal response is comparable to similar lasers made onn-type substrates. A small-signal -3-dB frequency as high as 16.4 GHz has been measured with a 175- μm-long laser. The laser responds to large-signal digital word sequences at rates of 16 Gbit/s.     

Generalized likelihood signal resolution

This paper defines anM-ary generalized likelihood ratio test (MGLRT) that overcomes Root's early objection to the application of generalized likelihood ratio testing to the resolution of correlated signals. The proposed test extends the form of a conventional binary generalized likelihood ratio test (GLRT) in a manner that permits a generalization of the minimax properties of the binary test to theM- hypotheses case. When the estimated signals are orthogonal, the test reduces to a sequence of conventional binary tests duplicating the performance of a narrow-band matched filter envelope-detector receiver.     

Electrodynamics of rotating relativistic electron beams

On the basis of the Minkowski formulation, this paper discusses the basic laws governing the small-signal fields propagated along an electron beam which is rotating around its axis with constant angular frequency of rotation and drifting in the axial direction at constant relativistic velocity. In the first preliminary section are described the dc conditions for getting a stable relativistic electron beam in the presence of neutralizing ions with arbitrary number density and externally applied static magnetic field. Then, after a brief discussion of the ac-field equations, the constitutive relations for small-signal fields are obtained in both the laboratory frame, which is assumed to be an inertial frame, and the rest frame of the electron beam, which is not an inertial but a rotating frame. The rotating relativistic electron beam is found to be a nonuniformly moving dispersive medium or, more specifically, an inhomogeneous bianisotropic medium with space and time dispersion. With the use of the constitutive relations derived above, the following sections consider the energy and momentum for the small-signal fields, and their conservation relations, together with their transformation laws between the laboratory frame and the rest frame of the electron beam. Our discussion includes, as the special cases, all the important cases of an ion-neutralized or axially confined beam and the Brillouin beam.     

Analysis of a low magnetic field TE m11 gyroklystron amplifier†

Large- and small-signal numerical calculations are presented for a two-cavity, low magnetic field gyroklystron amplifier operating in the TE _m11 whispering-gallery mode. The gyroklystron system modelled consists of a bunching cavity and an output cavity separated by a drift tube. For operation of both cavities at TE₅₁₁, gain and emission efficiency are studied for a high energy (γ = 1·6), low axial velocity (β_Verbar; = 0·1) electron beam. Prebunching prior to the output cavity in the gyroklystron leads to an increase of the maximum efficiency by more than a factor of two over that obtained from operating the output cavity as an oscillator. Model calculations are presented which show that magnetic field tapering greatly reduces the effects of any initial axial velocity spread in the electron beam, allowing high gain (?40 dB) and high efficiency (25-30%) to be achieved.     

Small-signal gain and time-resolved spectroscopy of the D2-F2/CO2pulsed chemical transfer laser system

Measurements made of the small-signal gain and time-resolved spectral output of a flash-initiated D2-F2/CO2chemical transfer laser system are reported. Small-signal gain measurements indicate a possible lack of rotational equilibration among the rotational levels of the CO2during the DF-CO2V-V energy transfer process. Time-resolved spectral output of this system, operated as a laser oscillator, is presented as verification of the small-signal gain results.     

Kinetic theory of a novel carm oscillator with axisymmetrical quasi—Optical cavity of oblique rotation at arbitrary angle

A novel CARM oscillator with axisymmetrical quasi—optical cavity of oblique rotation at arbitrary angle (AQCORAA) is studied using the kinetic theory. By means of the method of local field expansion in the coordinates of the guiding centre and the Laplace transform, the beam—wave interaction power, starting current density and frequency shift are derived. The formulas presented here may have some potential applications for more further studies of the CARM oscillator with AQCORAA.     

Controlled energy extraction and sharp nanosecond pulses from an HF amplifier

We report complete spatial control of laser energy extracted from an electron-beam-initiated HF amplifier. Control was achieved by application of a weak oscillator beam, which, by extraction of all of the available energy, overcame amplified spontaneous emission. In a separate experiment, temporal control was also demonstrated. Short (4-ns) sharp (contrast ∼20) amplified pulses were obtained by rapid polarization rotation and selective reflection in the amplified beam.     

A new electron gun for picture display with low drive signals

The paper discribes an approach to the problem of picture tube guns for small signal service. A Pierce-type cathode delivers a collimated parallel beam of 1600 microamperes at 250 volts (microperveance: 0.4). This beam is injected into a cylindrical cavity of appreciable length (3/4-inch long, 1/4-inch diameter). It is focused upon a small aperture at the far end using a parabolic axis potential. This axial focusing field is approximated by three cylinder segments at two intermediate voltages. To modulate the beam by lateral deflection, the cavity is again bisected through an axial plane and signal voltage is set up between half cylinders. This modulation by two crossed-electrostatic fields ("CFM" modulation) has been successfully applied in transistorized television, using a seven-volt video signal on a beam of 900 microamperes.     

A small-signal analysis of the electron cyclotron backward-wave oscillator

In an earlier report on the construction and performance of the electron cyclotron backward-wave oscillator, it was shown, through physical arguments, that in an unloaded waveguide supporting the dominant mode, an electron having transverse rotation at its cyclotron frequency will interact with RF fields of approximately equal frequency. This transverse motion will deliver energy to the RF E fields and interact with the RF H fields, thus producing longitudinal bunching. A small-signal analysis is presented in this paper. With the use of the normal mode expansion analysis, the circuit equation is obtained by considering the normal mode in approximate synchronism with the beam. The RF current is computed by considering electron motion under the dc and circuit fields, but neglecting RF space-charge fields. Combining these equations leads to a sixth-order equation of propagation constants. Two waves are far from synchronism and are therefore neglected; the remaining four are two waves which originate from the "fast cyclotron waves" and two waves which originate from the forward and reflected circuit waves. The "fast cyclotron wave" so obtained has a different meaning from the usual definition and is discussed in detail. Theoretical start-oscillation current is found to depend critically on the reflection coefficient at the electron gun end. Proper adjustment of this parameter leads to excellent agreement between the theoretical and experimental start-oscillation currents.     

GTD analysis of the E-plane patterns of conical horns

An analytical procedure for predicting accurately theE-plane patterns of conical horns with moderate aperture widths (ka < 10), based on uniform geometrical theory of diffraction (UGTD) and supported by measured data, is presented. This analysis predicts theE-plane patterns more accurately (over the main beam) than the one presented earlier.     

Stimulated Brillouin and Raman scattering for the generation ofshort excimer laser pulses

In this experimental work, the SBS and SRS processes were used in order to produce UV laser beams of good optical quality and short time duration. An XeCl oscillator and a double-pass amplifier with a phase-conjugate mirror via stimulated Brillouin scattering, generate the laser beam at 308 nm to pump a Raman cell. The oscillator pulse was 11 ns long, while the amplified phase-conjugate beam duration could vary from 3.3 to 1.5 ns, due to the compression operated by the Brillouin mirror. When this last laser beam was focused into a Raman cell containing methane at 30 atm, the shortest backward stimulated Raman scattering pulse at 338.4 nm was 170 ps long with 0.4 ml of energy. The 338.4-nm wavelength is interesting for the production of short bunches of cold electrons from Mg and Zn targets     

Forward scattering from cylinders of triangular cross section

The induced-field ratios (IFR) of conducting cylinders of a triangular cross section have been calculated. When the width of the cross-section is in the range of 1-2 wavelengths, theE-wave IFR's are substantially less than the corresponding values for square or circular cross sections. From the standpoint of RF aperture blocking of a reflector antenna, the triangular cross section thus offers an advantageous cross section for feed-support struts.     

Phase Feedback for Nonlinear MEM Resonators in Oscillator Circuits

In this paper, a phase feedback approach for using nonlinear microelectromechanical (MEM) resonators in oscillator circuits is investigated. Phase feedback makes use of the oscillation phase condition for oscillator circuits and enables fine-tuning of the frequency at which the resonator oscillates by means of setting the phase in the feedback amplifier. The principle of the approach is illustrated for a nonlinear Duffing resonator, which is representative of many types of MEM resonators. Next, the approach is applied to an electrostatically actuated nonlinear clamped–clamped beam MEM resonator, on simulation level. Phase feedback allows for operation of the resonator in its nonlinear regime. The closed-loop technique enables control of both the frequency of oscillation and the output power of the signal. Additionally, optimal operation points for oscillator circuits incorporating a nonlinear resonator can be defined. Application of phase feedback results in more robustness with respect to dynamic pull in than in open-loop case, however, at the cost of a deteriorated phase noise response.      

An approximate formula for calculating the directivity of an antenna

An approximate general formula to calculate the directivity of an antenna based upon theE-plane andH-plane patterns is proposed. For narrow beam patterns, the directivity is expressed in terms of the half-power beam widths of the main patterns. The better approximation of the formula presented here over the geometrical mean formula is pointed out.     

Circumferential distribution of scattering current and small hole coupling for thin finite cylinders

The scattering current induced on a thin finite conducting cylinder immersed in a"theta"-polarizedE-field is studied. Particular attention is paid to the circumferentially nonuniform mode as theE-field angle of incidence varies. This nonuniformity is shown significant (peak-to-average ratio of 3 dB at cylinder midlength) at certain incidence angles for wavelength long cylinders with diameters as small as0.067lambda. Also investigated is the relationship between scattering current and cavity response patterns for narrow thin-walled cylindrical cavities with small holes through which energy is coupled. It is demonstrated theoretically, with experimental verification, that the circumferential variation of scattering current strongly affects the fields within thin cylindrical cavities having apertures with small circumferential extents. It is noted, however, that for most thin-body radiation and scattering problems (in contrast with aperature coupling) only the uniform current mode is significant.