Electromagnetic field measurements a millimeter wave linearaccelerator

Perturbational field strength measurements suitable for use on a proposed 120-GHz 50-MeV electron linear accelerator are described. The measurements are used to determine the R/Q of the device, where R is the shunt impedance. The perturbation is achieved by the use of hollow metallic cylinders with diameters ranging from 25 to 127 μm which are approximately 500 μm long. The cylinders were fabricated by sputtering aluminum through a shadow mask onto silica optical fibers as well as nylon surgical thread. The perturbational “form factors” for such a geometry are experimentally determined using a pillbox cavity. The measured values for the form factors are compared to theoretical estimations, which result in simple analytical expressions. The measured form factors are also compared to values calculated from a finite difference model of the perturbing object. The R/Q for various accelerating modes is measured on a 12-GHz model of the 120-GHz structure. Results are compared to predictions from a finite difference model of the accelerating structure     

毫米波室内传播的场强测量

介绍了毫米波室内传播的场强测量。通过对测量的数据进行处理,可得无论使用全向天线还是定向天线作为接收天线,路径损耗指数都约等于２。慢衰落的累积概率分布符合对数正态分布。快衰落的累积概率分布在没有直达波的民政部下符合瑞利分布,而在有直达波的情况下,如果使用全向天线则趋向瑞利分布,使定向天线符合莱斯分布。     

亚洲地区黑碳气溶胶外场在线观测研究进展

黑碳气溶胶是化石燃料和生物质不完全燃烧的产物之一, 不仅影响着空气质量和人体健康, 还通过吸收太阳辐射改变辐照平衡从而影响区域乃至全球气候。亚洲地区作为世界七大洲中人口最多、面积最广的地区, 黑碳气溶胶排放量占全球排放量二分之一以上。对当前黑碳气溶胶观测所用主要仪器与方法, 以及亚洲地区从上世纪九十年代至今有关黑碳气溶胶的观测结果进行了系统性总结。通过总结发现亚洲地区大气黑碳浓度分布特征与人口分布特征相一致, 中国地区黑碳浓度分界线与胡焕庸线大致吻合, 佐证了黑碳主要受人为活动影响的结论;并进一步分析了亚洲地区黑碳排放来源及影响因素,以及黑碳光学性质的最新研究成果;最后总结了当前研究中存在的不足, 并对黑碳气溶胶未来研究方向提出了展望。     

Method for radar cross section measurements in millimeter and submillimeter wave regions

We present a new method for electromagnetic modeling radar scattering processes. In this method we use a quasi-optical waveguide of the type of "hollow dielectric waveguide" as a fundamental component of radar cross section (RCS) instrumentation systems. Such waveguide structure produces required target-illuminating quasiplane wave and suppresses unwanted waves as well as transmits the legitimate signal from test object, mounted inside this waveguide, to the reception zone. Presented method is especially effective one in millimeter and submillimeter wave regions, in particular, for investigation RCS of targets with small reflectivity.     

Laboratory measurements of polarization radios of wind wave surfaces

Polarization ratios (sigma_{vv}/sigma_{HH}) of wind-generated rough water surfaces are studied experimentally by means of radar backscatter power measurements. The measurements were made at 9.23 GHz with incidence angles between45degand55degfor wind speeds between 3 m/s to 10 m/s. Scattering surface statistics at all wind speeds were also measured by means of a wave height gauge and a laser slope gauge. The polarization ratio data are presented against parameters pertinent to scattering theory, which are obtained from the measured surface statistics. The results are compared to "composite surface" theory calculations for an assumed wave-height spectral density of the formF(k) propto k^{-m}, wheremis an adjustable parameter.     

Centimeter and millimeter wave attenuation by atmospheric gases and rainfall at a tropical station

The radiowave attenuation due to oxygen and water vapour has been computed over the frequency range 3–350 GHz making use of the mean surface air pressure, temperature and water vapour at Ile-Ife (geog. lat 7.5°N, long 4.5°E) in Southern Nigeria. It is observed that the attenuation at this tropical location is generally higher than at temperate climates. A similar analysis was performed for rainfall attenuation using rainfall intensity measurements. The results obtained with three different expressions for the rain height showed that a rain height of 3 km is a reasonable assumption for estimating earth-space rainfall attenuation at this location. It is found that for frequencies above 200 GHz, the polarization dependence of the specific attenuation due to rainfal becomes negligible. The computed attenuation is lower that that predicted using the corresponding CCIR rain climate data. The results show that whilst the contribution of oxygen and water vapour to the total atmospheric attenuation could be neglected when compared with rainfall attenuation up to about 150 GHz, the contribution becomes significant for frequencies above 190 GHz.     

W波段的毫米波通信

由于其载波频率更高,W波段可支持更大的带宽和更高的传输速率。因为大气损耗小,W波段信号能够进行远距离传输。进行了W波段信号的链路分析,开展了W波段毫米波通信实验的研究。由光生毫米波方法测得W波段传输系统的频率响应在10 dB变化范围内,然后采用电生毫米波系统,进行距离分别为0.8 km,1.2 km及4.4 km的W波段信号的无线传输实验。测得的接收功率分别为-19.77 dBm,-30.85 dBm及-38.61 dBm,验证了W波段信号的远距离传输特性。     

Synchronous measurements of the atmospheric radio emission in the two and three millimeter wavelength regions

Apparatus and procedure of measuring the atmospheric radio emission simultaneously in two atmospheric windows are described. The results of measurements of the sky brightness temperature and obtained atmospheric optical depth values are reported. The diurnal and seasonal variations of the sky temperature and zenith absorption as well as their relation to weather parameters of nearsurface atmospheric layer are discussed.     

Submillimeter wave communication versus millimeter wave communication

This paper studies the performance of a submillimeter wave antenna operating between frequencies 0.1 THz and 10 THz with a 4-cyano-4-pentylbiphenyl [5CB] substrate. Since the size and shape of the antenna impact its gain/directivity, resonant frequency, bandwidth, and efficiency, the two antenna types considered in this paper are: (a) Rectangular Patch Antenna (RPA), and (b) Cylindrical Dielectric Resonator Antenna (CDRA). Here a submillimeter wave antenna is compared with a millimeter wave (a few GHz to 100 GHz) antenna. These popular mm-wave antennas are chosen for the submillimeter wave antenna in order to understand changes in their performance as the result of changes in their geometrical shape. FEldberechnung bei Korpern mit beliebiger Oberflache (FEKO) software is used for the design and calculation of the Three-Dimensional (3D) ElectroMagnetic (EM) patterns. This paper also concentrates on the design and analysis of a massive submillimeter wave Multiple-Input Multiple-Output (MIMO) (8 by 8) RPA and CDRA.     

Point-source suppression for atmospheric wave extraction from airglow imaging measurements

Spectroscopic images of atmospheric chemiluminescent airglow contain fundamental diagnostic information about the structure and dynamics of the upper atmosphere. However, westward movement of stars causes non-negligible contamination in the two-dimensional horizontal wavenumber spectra extracted from all-sky airglow images. The conventional star-removing scheme is not effective in attenuating the star artifacts in the spectra of emission intensities of gravity wave perturbation, hindering the subsequent calculation of the angular spectra and the momentum fluxes of the profiles. To address this problem, a gradient-based edge detection algorithm for locating and attenuating the undesired star signal is developed. Comparatively, this algorithm is more effective than the conventional star-removing methods. The algorithm is validated in the context of experimentally obtained spectra.     

Monolithic millimeter wave optical receivers

A single stage monolithic millimeter wave optical receiver circuit was designed and fabricated using a metal-semiconductor-metal (MSM) photodetector and a pSeudomorphic Modulation Doped Field Effect Transistors (SMODFET) on a GaAs substrate for possible applications in chip-to-chip and free space communications. The MSM photodetector and the SMODFET epitaxial material were grown by molecular beam epitaxy (MBE). Device isolation was achieved using an epitaxially grown buffer between the MSM detector layers and SMODFET. The photodetector was designed for maximum absorption at optical wavelength of 770 nm light and the SMODFET impedance matching network was optimized for 44 GHz. The monolithic millimeter wave optical receiver circuit achieved 3 dB gain over a photodetector at 39 GHz, which was the limit of the measurement system. TOUCHSTONE model of the circuit indicated 6.6 dB gain over the photodetector and 5.7 dB total gain including the insertion loss of the photodetector at 44 GHz     

Measurements of near millimeter wave atmospheric attenuation in the temperature range 259K to 282K

Field measurements of absorption of near millimetre waves by the atmosphere at temperatures below 280°K have confirmed that there is an additional absorption component characterised by a much larger temperature exponent than can be attributed to water dimers in equilibrium.     

Holographically steered millimeter wave antennas

A class of dynamic holographically addressed millimeter wave antennas becomes possible by combining the principle of holography with the notion of microwave transparency produced by excess carrier generation in semiconductor panels or preferably by reflectivity modulation of an interferometric structure consisting of a dielectric air gap metal structure. The theory of operation of the holographically addressed antenna is presented together with a discussion of possible methods for its implementation. The advantages of using a microwave Kinoform for this purpose are also pointed out.     

Embedding impedance of a millimeter wave Schottky mixer: Scaled model measurements and computer simulations

Using scaled model measurements at 2.5–12 GHz the embedding network of a 3 mm Schottky diode mixer has been developed. The noise performance of a cryogenic millimeter wave receiver was simulated by computer applying the developed equivalent circuit and diode parameters. The effects of impedance match at the fundamental frequency as well as at harmonic frequencies were studied. Also the effect of diode I-V-curve steepness was studied. The calculated results were compared with the experimental noise performance.     

Cad of millimeter wave power combiners

The computer-aided design and optimisation of millimeter wave power combiners are investigated based on a frequency-domain harmonic balance technique, where the external-circuit mutual impedances looking outside from two active devices are calculated with a mixed technique of modes expansion, Galerkin, and collocation methods.     

A study of millimeter wave cusptron

The interaction between electron beam and RF fields of H₈₁₁ π-mode in an eighth harmonic cusptron at f₀=35GH_z is studied numerically. The finite thickness and eccentricity of a rotating annular electron beam and the cusp magnetic field in the imbalance case (B_c≠?B₀) are considered in the mumerical calculation. The results show that these pratical factors have a great influence upon the electron efficieency.     

Design of millimeter wave microstrip reflectarrays

This paper discusses the theoretical modeling and practical design of millimeter wave reflectarrays using microstrip patch elements of variable size. A full-wave treatment of plane wave reflection from a uniform infinite array of microstrip patches is described and used to generate the required patch-design data and to calculate the radiation patterns of the reflectarray. The critical parameters of millimeter wave reflectarray design, such as aperture efficiency, phase errors, losses, and bandwidth are also discussed. Several reflectarray feeding techniques are described, and measurements from four reflectarray design examples at 28 and 77 GHz are presented     

Accurate millimeter wave antenna phase pattern measurements usingthe differential phase method with three power meters

The novel differential phase measurement method has been demonstrated at millimeter waves using three power meters instead of a phase-sensitive measurement device. Compared to conventional antenna phase measurement methods, the differential phase method provides several advantages. This method requires no rotary joints or flexible cables. Phase-locking of the oscillators is not necessary. It is shown that the phase measurement device can be replaced by three power dividers and three power meters or detectors. The phase patterns measured with three power meters agree well with the measurements carried out using an antenna measurement receiver as well as with the theory