Excess attenuation of millimeter waves at window region due to atmospheric water vapor

Journal of Infrared, Millimeter, and Terahertz Waves - The attenuation of 245.52 GHz millimeter wave was measured through a near ground horizontal path in order to study the anomalous water vapor...     

Circular groove guide for short millimeter and submillimeter waves

A new type of groove guide, circular groove guide, has been designed for use as a low losses, high power handling, low dispersion and single mode transmission medium in the short millimetric and submillimetric waves ranges. The characteristic equations of TE modes and TM modes have been developed and the propagation characteristics of the fundamental mode have been discussed. Experimental measurements are in good agreement with theoretical results     

An interconnected 2D-TM EBG structure for millimeter and submillimeter waves

Due to their unique properties, electromagnetic bandgap (EBG) materials are of high interest for applications in communication technology for many frequency bands from microwave up to optical frequencies. We have investigated in both simulation and experiment a two dimensionally periodic EBG structure made by reactive ion etching of silicon with a bandgap for transverse magnetic waves in the millimeter wave range around 100 GHz. The structure comprises both a large bandgap and a high mechanical stability due to interconnecting dielectric bridges.     

Metal mesh couplers using evanescent waves at millimeter and submillimeter wavelengths

In this paper we introduce a metal mesh evanescent wave coupler that makes use of evanescent wave coupling between a metal mesh and a dielectric plate, as a quasi-optical component for millimeter and submillimeter wavelengths. The transmission properties of this type of couplers have been investigated experimentally and theoretically for both capacitive and inductive metal meshes in the frequency range from 40 GHz to 60 GHz. The transmittance of a capacitive metal mesh evanescent wave coupler can be adjusted more than 70% by changing the spacing between the capacitive mesh and the silicon plate less than 0.15 mm at around 57 GHz.     

A multipath model for atmospheric scintillations at microwaves and millimeter waves

The paper describes a deterministic model for the effects of atmospheric turbulences on satellite-earth links from 1 to 100 GHz. Turbulent cells are considered as dielectric volumes crossing the Fresnel's zones of the link. The transmission coefficients are calculated for point receivers as well as for actual aperture antennas. The model yields a transfer function submitted to the influence of the equivalent dielectric constant, the thickness, size, and geometry of the cells, the size of the antenna, and the operating frequency. The resulting group delay is also evaluated, as well as the impulse and step-responses.     

On the anomalies in submillimeter absorption spectrum of atmospheric water vapor

Using a tunable source of monochromatic radiation (BWO) and a pneumatic detector, the field and laboratory investigations have been performed to obtain spectral distribution of atmospheric water vapor absorption coefficient in transparent windows centered at the wavelengths of 0.88 and 0.73 mm. The measurements have not found any spectral features mentioned repeatedly in the literature, besides the usually observed excess of the measured absorption above the calculated one for water vapor monomers.     

Resonator systems for klystrons of millimeter and submillimeter wave bands

Design problems of resonator systems for klystrons of millimeter and submillimeter wave bands are considered. It has been shown that, for efficient interaction of the resonator’s field and the electron beam in such devices, it is necessary to use resonators with high wave impedance. A quality factor, which allows one to compare resonators having different shapes, has been introduced. Different means of increasing the resonator’s wave impedance and circuits coupling resonators to input and output transmission lines have been investigated.     

Theoretical performance of novel multipliers at millimeter and submillimeter wavelengths

A theoretical comparison of various low and high order multipliers for 200 GHz and 1 THz has been carried out. Novel diodes including single barrier varactors, barrier-intrinsic-n⁺ diodes and high electron mobility varactors are shown to have excellent theoretical performance, comparable or better than the conventional Schottky varactors for single and double diode frequency multipliers at millimeter and submillimeter wavelengths, whereas quantum well diodes, since they suffer from high resistive losses, are shown to be less attractive. In comparison to the conventional Schottky varactor, these new diodes have some potential advantages in their characteristics such as nonlinearity or a special symmetry. For future optimization some general comments on these advantages as well as other factors affecting multiplication is given.     

Overwater propagation of millimeter waves

A field test program conducted to determine the short-and long-term fading characteristics and atmospheric absorption effects on an overwater millimeter-wave transmission path is described. A 6.1-nautical-mile overwater link was established using a 53-GHz transmitting frequency. Low grazing angles were used with antenna heights of 15 to 30 feet above sea level. The results of the program indicate 1) that short-term fading is Rayleigh distributed in the severest cases and is caused by surface reflections, and 2) that long-term fading variations occur more frequently and with greater intensity during warm weather periods.     

Remote probing of atmosphere and wind velocity by millimeter waves

A technique is developed to probe the atmospheric turbulence strengthC_{n}^{2}and the wind velocity along a path using millimeter waves as a tool. Data obtained in a line-of-sight millimeter-wave propagation experiment are processed and used as the source of information. The averagedC_{n}^{2}and wind velocity together with their gradients along the propagation path are calculated by inverting a set of integral equations. A numerical method is used to yield the least-square-error solutions. Comparison is made between the theoretically calculated wind velocity over a 33-hour period and that measured by a conventional anemometer.     

Reflection of millimeter waves by a corrugated dielectric slab waveguide

The TM wave propagation in a corrugated dielectric slab has been studied using a singular boundary perturbation procedure, which is supported subsequently by experiments in the millimeter-wave region.     

Reflection of millimeter waves by a corrugated ferrite slab waveguide

The electromagnetic wave interactions in a corrugated ferrite slab have been investigated using a singular boundary perturbation procedure, which are supported subsequently by experiments in the millimeter-wave region.     

Investigation of iron borate on the submillimeter waves

Antiferromagnetic resonance (AFMR) in iron borate at the frequency of 300 GHz at the room temperature in weak (down to 0.1T) external magnetic fieldH has been studied. The loss in AFMR line increased or decreased depending on the direction and magnitude ofH. Such properties ofFeBO ₃ monocrystals allows to design undirectional and modulation devices.     

Laboratory millimeter wave measurements of atmospheric aerosols

Measurements made in an untuned resonator by Fourier Transform Spectroscopy of atmospheric aerosols are explained by a pumped phonon model due to Fröhlich.     

Dielectric slow-wave structures for the generation of power at millimeter and submillimeter wavelengths

Several new types of coupling structures, designed to extract energy from a megavolt electron beam at a harmonic of the frequency used to modulate the beam current, are considered. In particular, the advantages of a slow-wave device over a right cylindrical cavity are indicated. The slow-wave coupling device may be resonant or nonresonant; the latter corresponds to a Cerenkov radiator. Power measurements at the twelfth harmonic of the fundamental modulating frequency provide good correlation with the theoretical power output expected. The design of a submillimeter coupling device is described, and the theoretical pulsed power obtainable is shown to be at the milliwatt level for a harmonic current density of 74 ma/cm².     

Local and non-destructive diagnostics of high-Tc superconductor layers by millimeter waves

For the first time millimeter waves are used for non-destructive diagnostics of superconducting layers and their quality control. The quality of the whole layer depending on T_C and δT_C is determined by local transmission of millimeter waves.     

Modeling of the calculation of the atmospheric chlorine monoxide content from the data of ground-based observations at millimeter waves

Computer modeling of the calculation of the content of chlorine monoxide in the atmosphere is performed. Radiation spectra of the substance that are measured at 204 GHz with an optimized ground-based spectroradiometer, currently under development at the Lebedev Institute of Physics, are used in the calculation procedure. It is shown that these spectra can be used to determine the average chlorine monoxide content in atmospheric layers and to reconstruct the vertical profile of this content by means of an algorithm based on the Tikhonov regularization method. The accuracy of determination of the content is estimated for different heights, including the heights of the layers that are most sensitive to atmospheric pollution.     

Damage and erosion at ceramic Windows due to high-power millimeter waves

The damage that occurs at alumina windows of high-power millimeter wave gyrotrons operating in TE_0,n mode is investigated. This damage appears only on the air side of the window where it yields small spot-like features (diameter <1 mm) and circular "melting" patterns (diameter >1 cm). The damage observed is thought to be related to rf field enhancements by resonances of trapped electromagnetic modes and by protrusions and contaminations of the ceramic surface.