Pulsed wideband orotrons of millimeter and submillimeter waves

We have developed a series of low-voltage orotrons operated in the short-wave part of the millimeter and long-wave section of the submillimeter wavelength range. The use of an open resonator as the electrodynamic system of the orotron ensures high stability of the radiation frequency and a wide band of frequency tuning. The output orotron power achieved experimentally amounts to hundreds of milliwatts, which is sufficient for many promising spectroscopy methods. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 11, pp. 958–963, November 2006.     

Planar orotron experiments in the millimeter-wavelength band

The planar orotron is introduced and shown to be a viable source of moderate power and of millimeter and submillimeter wavelength radiation. The resonator is a slow-wave structure consisting of a rectangular metal grating which is opposed by a planar conducting boundary. The device operates in the surface harmonic mode: electrons interact with axially traveling waves which evanesce above the grating surface, and the amplified radiation leaves the resonator in parallel with the beam axis. Operation in both the forward and backward mode is possible. The resonator cavity is designed to enhance longitudinal reflections, and thereby enhance the output power and efficiency. The output frequency and tuning range are determined by the grating parameters. Experiments performed in the backward mode have produced radiation from 30 to 110 GHz at power levels ranging from 100 W to 2 kW. The efficiencies vary from 1 to 7%. The measured frequencies are closely predicted by a theory which is also presented     

Methods of Calculation and Parameter Control of the Eigenmodes of a Simple Two-Mirror Cavity

Methods of spectrum calculation and parameter control of open-cavity eigenmodes are presented. The potential of the proposed software and hardware is demonstrated on the basis of an orotron cavity model designed and examined for millimeter wavelengths. The numerical and experimental results are in good agreement. The developed methods and software can be used for designing open cavities in various frequency ranges.     

Resotron: A Novel Tunable Millimeter and Submillimeter Wave Source of Radiation

The need for tunable radiation sources in the millimeter and submillimeter range for spectroscopic purposes is still a research area of great interest. The tunable radiation source, proposed in this paper, is a special free electron laser device with the prerequisite of low electron energy. The output power density in the millimeter (GHz)-range is of the order of MW/cm² and in the submillimeter (THz)-range of the order of kW/cm². The device consists of an electron source with electron optics, wiggler/microwiggler, and a longitudinal magnetic field. The wiggler for the THz-regime has a very short wiggler period of approximately 400 m and could be manufactured with laser micromachining techniques. The free electron laser operates in magnetoresonance and shows surprisingly stable electron orbits and therefore narrow output frequencies. Computational results of the temporal behavior of the output power done with a multi-frequency code are reported.     

Excitation of orotron oscillations at the doubled frequency of a surface wave

We study theoretically an electron frequency self-multiplier in which a surface mode of a periodic system is self-excited at a low frequency for a comparatively low current. The electron bunches, which appear as a result of this, excite the volume mode of an open resonator at the doubled frequency (coherent Smith-Purcell radiation). The open-resonator scheme allows one to obtain the higher power and coherence degree of radiation compared with the presently popular frequency multiplication scheme with an open periodic system (diffraction grating). The weakly relativistic and relativistic variants of the multipliers with a two-mirror open resonator designed for obtaining a high-power coherent radiation in the short-wavelength part of the millimeter and submillimeter ranges are studied numerically. The developed approach can also be used for designing high-power frequency multipliers on the basis of an array of nonlinear solid-state elements.     

Submillimeter Wave ESR Measurement for Cr3+ in Ruby Crystal Using a Gyrotron as a Radiation Source

Fine structure constant of ruby has been measured using an ESR spectrometer with a pulse magnetic for high fields and a gyrotron as a radiation source in a millimeter to submillimeter wave range. The measurement was carried out at room temperature. The Zeeman energy in this frequency range is large enough compared with the fine structure constant. The higher order term in the effective spin Hamiltonian can explain the dependence of fine structure constant on the frequency. The observed fine structure constants depend on the field intensity.     

Frequency synthesizers up to 370 GHz

A new generation of frequency synthesizers up to 370 GHz is described. The main parts of them are microwave frequency synthesizer covering 11–15 GHz band, effective frequency multipliers-mixers using an opposite pair of planar Shottky diodes and a lock-in loop of a backward-wave oscillator tube covering millimeter and longer part of submillimeter wave bands with tens of milliwatts of output power. The ways of further increase in the operating frequency of such synthesizers are discussed.     

High Power, Frequency Tunable, Submillimeter Wave ESR Device Using a Gyrotron as a Radiation Source

ESR device using a submillimeter wave gyrotron as a radiation source and a pulse magnet for high field up to 30 T has been constructed. Our gyrotrons (Gyrotron FU series) were developed as millimeter and submillimeter wave radiation sources and have attractive advantages for ESR spectroscopy, for example, high power and frequency tunability over broad range. The ESR device has been successfully applied to three cases of ESR measurements. In the first case, the temperature dependence of ESR was measured for a typical antiferromagnetic material MnO at the frequency of 301 GHz. In the second case, the dependence of the fine structure constant of the ruby on the magnetic field intensity was measured in the millimeter to submillimeter wave region. In these two cases, the gyrotron was operated by complete cw mode. In the final case, a pulse technique was applied to the ESR, the gyrotron was operated in pulse mode and the pulsed magnetic field was generated in the synchronized phase with the gyrotron operation.     

The Millimeter Band Oscillator in the Large-Orbital Resonance Mode

The millimeter band oscillator operating in the specific large-orbital resonance mode is considered. A theoretical analysis of energy oscillator characteristics is made. According to the early estimates, this system is free from some shortcomings typical for a gyro-devices when an operating wavelength becomes shortened to a millimeter and submillimeter band.     

Millimeter wave phase-locking in distributed Josephson arrays

Voltage tunable oscillators operating at millimeter and submillimeter wavelengths can be designed and fabricated using series arrays of Josephson junctions. The coherent radiation obtained from such oscillators results from the mutual phase-locking of the junction through the high-frequency Josephson current generated in the array. A 40-junction array of Josephson junctions distributed over many wavelengths has been designed, fabricated and tested for operation at 100 GHz. This paper presents the experimental results obtained for this prototype array. A review of the theory for optimizing array design is presented along the implications for power generation at submillimeter wavelengths in future arrays.     

Broadband Analysis of Holographic Power Combining Circuits

Holography is a promising technique for power combining applications in the frequency range of short millimeter and submillimeter waves. In this paper, quasi-optical holographic power combining circuits are investigated. An equivalent network is utilized which rigorously models horn arrays and biperiodic dielectric structures in order to design computer-generated holograms. We apply the network model to a 5-element quasi-optical power combiner and demonstrate its capability. The hologram is designed for 150 GHz and has an efficiency of 92.5 % with a 90 % bandwidth of 5.3 %. With the aid of a broadband waveguide power divider and a vector field measurement system, the circuit is analyzed.     

Development of frequency tunable, medium power gyrotrons (GyrotronFU series) as submillimeter wave radiation sources

High frequency, medium power gyrotrons (Gyrotron FU series) have been developed at Fukui University as radiation sources covering a broad band from millimeter to submillimeter wave region. They have already been applied to high frequency electron spin resonance and to submillimeter wave scattering in plasma. Many parameters of the gyrotron series could be useful for applications in several new areas. The development and some applications of the Gyrotron FU series are summarized in this paper     

Quasi-optical antenna duplexers

The development of antenna duplexers for transceiving quasi-optical systems of millimeter and submillimeter wavelengths are considered for two groups of devices — passive and active action. Duplexers, using properties of quasi-optical hybrids, belong to the first group, and duplexers on the base of semiconductor or ferrite devices are included to the second group. Results of developments and investigations of considered devices in the millimeter wave range are presented.     

Evolution of discharge structure in capacitive radio-frequency atmospheric microplasmas

Conventional radio-frequency (rf) nonthermal atmospheric plasmas are generated in a millimeter gap. In this Letter, we present a self-consistent numerical study of rf atmospheric microplasmas in a submillimeter gap comparable to their sheath thickness. It is shown that the narrow electrode gap deforms the discharge structure, ultimately removing the bulk-plasma region and disabling electron trapping. Significantly, these properties permit rf atmospheric microplasmas to operate at very high current densities thus simultaneously achieving higher stability and greater chemical reactivity.     

Gunn diodes with different cathode contacts oscillation on harmonic frequencies

The studies of Gunn diodes on the basis of GaAs with different types of cathode contacts, the profile of doping, the active area length and temperature at frequencies of the second and third harmonics were carried out to obtain effective oscillation in the millimeter and submillimeter ranges.     

On the anomalies and role of water clusters in atmospheric absorption of millimeter and submillimeter radio waves

Experimental data are presented which do not confirm the existence of anomalies observed by many investigators in the atmospheric absorption of millimeter and submillimeter radio waves and make questionable the hypothesis on the importance of large water clusters in absorption that is invoked to explain the anomalies.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 4, pp. 483–495, April, 1996.This work was supported in part by the Russian Foundation for Fundamental Research under Project No. 94-02-05407-a).     

Theory of resonant relativistic oscillator with nonuniform focusing field

The two-dimensional model of millimeter wave resonant O-type oscillator (as orotron, ledatron, resonant BWO, etc.) with a relativistic electron beam is analyzed. The selfconsistent nonlinear simultaneous equations have been obtained for the arbitrary space distribution of the magnetic guide field. The start generation characteristics are analyzed under small-signal conditions with an analytical solution taken for the case of inclined focusing magnetic field. It is found that the efficiency of electron-wave interaction appreciably depends on the focusing field strength and the relativistic mass factor. The results of numerical optimization of the guide field structure are presented to show possibility of improvement of the start characteristics of the oscillator.     

Modern millimeter and submillimeter receiver systems for radio astronomy

In this review we consider the composition and placement of receiver complexes on millimeter and submillimeter wave radio telescopes as well as their components and circuitry. Examples of receiver complexes are given for both ground-based and space radio telescopes.     

Results of a survey on calibration standards requirements

This paper presents the results of a mail survey on the calibration and standards requirements of the millimeter submillimeter wave and far infrared research community. Brief accounts of the work in this area that is currently in progress at NBS and NPL are included.     

Microwave receiver system with quantum superconducting Josephson junctions based on LTSC and HTSC

The paper is concerned with the methods for frequency measurement in millimeter and submillimeter wave ranges using AC Josephson effect. Basing on the method the Microwave Superconductive Receiver System was designed. The main results obtained for niobium Josephson junctions and bridges made of HTSC, as a measurement element are presented.