An experimental radome panel evaluation

Modern antenna radomes are made of materials that tend to shed water to minimize their RF attenuation when wet. The microwave performance of these materials has been studied experimentally. Radome attenuation was measured as a function of frequency, rain rate, rain incidence angle, RF incidence angle, and polarization. The tests were performed on (1) new, clean radome panels, (2) used, dirty radome panels, (3) cleaned, used radome panels, and (4) panels treated with hydrophobic paint. The results show weak loss dependence on frequency over the 13-20 GHz frequency range of interest, which increases slowly with rain rate from 2.5 to 29 mm/h except for surfaces that are wettable, where the dependence on rate is much stronger. Loss is nearly independent of rain incidence angle, but it is strongly a function of surface condition. Hydrophobic paint is shown to be very effective. The test setup used, limitations imposed by the real world, and a simplified model of radome loss derived from the test results are described     

System performance in rain in a radome-enclosed environment

Computer modeling and analysis techniques have been established to evaluate performance during rain, in a radome-enclosed system. Electromagnetic transmission line theory using raytracing techniques is presented to compute transmission loss. Comparisons between theory and measured results are documented. Variations in water film thickness versus look angle and the resulting effect on performance are discussed. Other performance effects in rain, such as depolarization and noise temperature, are included in the analysis. The differences in performance using hydrophobic and non-hydrophobic materials can easily be predicted. Hydrophobic membrane materials are available for use with a radome, which yield excellent electromagnetic performance, even at mm wave frequencies. Recent tests are discussed which substantiate enhanced radome performance during rain.     

Signal level degradation due to snow accretion on a radome

The received signal level and antenna pattern variation due to snow accretion on a radome have been measured. Large signal level attenuation was observed when the snow accreted asymmetrically on the radome.     

水基附着介质罩对毫米波衰减的理论分析与实验研究

本文主要研究多种可能出现的天线罩水基附着介质对毫米波所产生的衰减.本文采用一个四层介质模型来模拟水附着在天线罩上的情况,根据Fresnel方程得到150 GHz和298 GHz电磁波衰减模型,通过测量纯水对毫米波所产生的衰减验证模型的正确性;再测量雨水、海水所产生的衰减,分析常见水基附着介质对毫米波所产生的衰减;最后测量不同盐度的海水对毫米波所产生的衰减,分析了海水盐度对衰减的影响.实验结果证明毫米波的衰减随着天线罩上附着水层厚度的增加呈现出较为规律性增长,而此衰减受中水中溶解物（微小颗粒和盐度）的影响较小.本文对毫米波雷达在雨天等复杂室外条件下的应用具有一定的指导作用.     

A streamlined metallic radome

The results of research and development, fabrication, and measured transmission performance for a specific streamlined metallic radome are contained in this paper. The measured results presented demonstrate that high-quality radome transmission performance can be attained with a streamlined metallic radome. The conical metallic radome presented is 6 ft 4 in long and has a base diameter of 25.5 in. The specially designed resonant slotted surface of the metallic radome consists of 90 percent metal and, for frequencies within its operating band, the radome permits transmission with any signal polarization over a wide range of scan angles. At its 8.90 GHz resonant frequency the metallic radome introduces less than 0.5 dB signal loss and less than 2 mrad boresight error. This radome has been purposely designed for operation over a narrow frequency band. Over a 200 MHz band, measured insertion loss and boresight error values of 1 dB and 6 mrad, respectively, are attained.     

磁性平板功率系数和插入相位移研究

该文采用电磁波反射、透射和传输线理论,建立了分析磁性平板功率传输系数和计算插入相位移的方法,给出了消除退极化现象天线罩材料电磁参数必须满足的数学公式。计算和分析了单层和典型A 夹层结构天线罩在电介质材料和磁性材料两种情况下表现出的传输特性,结果表明,磁介质平板材料电磁参数满足r = r (复介电常数等于复磁导率)时,可以避免退极化现象,功率传输系数优于对应的电介质平板,插入相位移变化更为平缓,表现出了最佳的传输特性。最后,利用商业软件HFSS 进一步验证了上述结论的正确性和该方法的有效性。      

Wet antenna effect on VSAT rain margin

The contribution of wet antennas to the antenna signal path losses in a VSAT environment is treated theoretically. The current commercial VSAT systems operating in either C-band or Ku-band generally have their remote terminal antenna reflectors and the antenna feed horn radomes coated with hydrophobic materials. The aim is to prevent the antenna and radome surfaces from becoming wet during a rainfall. This precaution relieves the burden of added rain margin necessary on the link budget. The magnitude of the propagation loss when the antenna reflector and the antenna feed horn radome surfaces are wet is determined. The results can indicate whether the expense of applying and maintaining the hydrophobic materials on the VSAT remote antennas and radomes is justified under specific loss conditions     

Depolarization properties of metal space frame radomes for use in satellite communication systems

Radomes have traditionally only been used in military satellite systems. However, higher availability civil applications are demanding their consideration in the higher frequency bands and for dualpolarization frequency re-use systems. This paper investigates the depolarization performance of metal space frame radomes and presents results of XPD for radome covered antennas in the 4/6 and 11/14 GHz bands and for antennas of 30, 11, 5 and 3 m diameters. It is demonstrated that current polarization specifications adopted in the INTELSAT system should be able to be met by radome covered earth-stations using conventional antennas.     

天线罩对抛物面单脉冲天线极化特性的影响机理和仿真分析

单脉冲定向技术是目前最准确的电子定向技术之一, 被广泛应用于微波毫米波跟踪、监视、通信、测量、天文观测等系统.为了保护雷达天线免受环境的影响, 许多单脉冲天线都采用天线罩, 这会对单脉冲天线方向图的极化结构产生影响, 另外, 有意的电子欺骗干扰如交叉极化干扰会对定向性能产生较大影响.文章以雷达导引头普遍采用的X波段抛物反射面幅度比较单脉冲天线为对象, 分析了抛物面结构、初级馈源特性、天线罩引起交叉极化分量的机理, 建立了典型物理参数下的计算模型, 在Ludwig第三定义下对加入天线罩前后单脉冲天线交叉极化特性进行仿真, 综合考虑了天线几何形状、偏置结构、天线扫描等因素对极化特性的影响.结果表明:多种因素会引起单脉冲天线显著的去极化效应, 复杂的方向图极化结构使得单脉冲雷达导引头的定向精度敏感于电波极化方式, 这为进一步开展交叉极化对抗单脉冲跟踪技术研究提供了重要理论基础.     

The Operation of Dual Polarized QAM Systems in the Presence of Depolarization Crosstalk and Differential Fading

The performance of dual-polarizedM-QAM systems is studied. By assuming coherence between the crosstalk and the desired signal, results are obtained for systems up to the modulation level of 64 QAM in each channel. Both balanced systems, with equal modulation levels in each channel, and unbalanced systems, with different modulation levels in each channel, are considered. Graphs are presented which show possible design tradeoffs to improve performance and suggest methods of system optimization. Each system is found to have an optimum value of relative transmitter power in the two channels. Analyses include the application of empirically based channel models giving relations between depolarization crosstalk, coplanar path attenuation, and differential fading levels.     

Measurements to estimate the relative permittivity and loss tangent of thin, low-loss materials

A thin layer of Kapton-, Kevlar-, or Tedlar-type materials is sometimes used in the construction of A-sandwich radomes to provide additional mechanical support to the outer skins of the radome, for example. The electrical properties (relative permittivity and loss tangent) of such materials are not always known beforehand at the frequency of interest. It is desirable that they be known in order to predict the likely RF response of the overall sandwich, assuming that electrical properties elsewhere are known. A simple S/sub 12/ transmission measurement can be carried out to provide measured data that can be used to good effect in a very simple formula (developed hereunder) to provide a useful working estimate for the electrical properties of such additional layers.     

Study of the local multipoint distribution service radio channel

Millimeter wave communication systems in the 21.5 to 29.5 GHz band are being developed in the United States and Canada for use in a local multipoint distribution service (LMDS). This paper summarizes radiowave propagation impairments for the LMDS and reports measurement data for small cells. Results include area coverage estimates over a range of basic transmission losses for 0.5-, 1.0- and 2.0-km suburban cells with foliated trees. Multipath, signal attenuation, depolarization, and cell to cell coverage also are discussed. Data indicates a high probability of non-line-of-sight paths due to trees which can cause signal attenuation and signal variability when wind is present. Signal variability was studied using k factors and compared to the Rician cumulative distribution function. Depolarization caused by vegetation and other signal scatterers was found to be an order of magnitude greater than rain-induced depolarization. A simple tapped delay line model is presented to describe multipath for three channel states     

Application of multi-layer structures of wafer-type made of composite materials for creating microwave antenna radomes

A new type of microwave antenna radome structure for aircrafts is suggested, which is a wafer radomes that possess improved characteristics if compared to traditional structures. Design peculiarities of such radome walls, wafer structures and their load-bearing elements made of dielectric composite materials are considered. A calculation model for such structures is justified and a methodology of selecting reasonable layer parameters according to radome’s level of radiolucency. A comparison of radio engineering characteristics of wafer and traditional three-layer structures of radome’s walls in a wide range of electromagnetic waves’ incidence angles in presence of mass limitations is conducted.     

Ice depolarization statistics for 19-GHz satellite-to-earth propagation

Observations were made at 19 GHz of depolarization due to ice crystals along a satellite-earth path with a38.6degelevation angle. The one-year data base included sufficient information to determine depolarization for any incident polarization angle. Depolarization was often observed in the absence of significant rain-produced copolarized signal attenuation. This depolarization is caused by ice crystals whose symmetry axes, as observed in the plane perpendicular to the direction of propagation, were usually within5degof vertical and horizontal. Maximum depolarization was observed for45deglinear or circular polarizations, and never exceeded -16 dB. For vertical and horizontal incident polarizations 8-10-dB lower maximum depolarization values were observed. Depolarization due to ice was also observed during most rain attenuation events. The unknown differential phase characteristics of rain-produced depolarization prevent further exact analysis of this ice depolarization.     

Première analyse des mesures de propagation oblique effectuées à Gometz-La-Ville sur le signal du satellite SIRIO 1

This paper discusses the results of measurements on the emissions of the Italian satellitesirio 1, carried out at the Gometz-la-Ville earth station during a one year period in order to assess the quality of future Earth-satellite links at frequencies above 10 GHz. The contributions of rain and snow to the measured attenuation are determined. The results are compared with those obtained by theccir prediction method. The attenuation due to a wet plane radome is evaluated. The variations of polarization decoupling as a function of attenuation are compared with those predicted by theoretical models and a method for determining the quality of the liaison when the same frequency is used on two orthogonal polarizations is proposed.     

Dependence of rain attenuation and cross-polarization on drop size distribution

Attenuation and cross-polarization due to precipitation are calculated for five drop size distribution functions, namely Laws-Parsons, Marshall-Palmer, Joss drizzle, Joss thunderstorm, and a renormalization of the latter. Propagation paths from the Communications Technology Satellite (CTS) and Comstar D1 synchronous satellites to Ottawa are considered. Clear weather antenna isolation effects are included in the results. We find that various drop size distributions introduce substantial deviations only in the attenuation versus rain rate curves. A proper normalization of the Joss thunderstorm model is important for attenuation. The deviations are much less in the crosspolarization versus attenuation plots, which are close together for all five drop size distributions. This is so even for the thunderstorm model at 28.56 GHz of Comstar D1, where the differential phase per unit length is decreasing at high rain rates. Unexpectedly, it is also found that for attenuation values not too large, the thunderstorm model provides less depolarization for a given attenuation as compared wth the other models.     

Estimation de la dépolarisation a partir des données d’affaiblissement pour les liaisons terre-satellite a plus de 10 GHz

In order to assess the performances of earth-satellite-earth ¦transmission¦ channels with frequency reuse by dual orthogonal polarizations propagation effects have to be taken into account which are of a statistical nature namely attenuation and depolarization. It is thought that to a first approximation rain depolarization is directly related to rain attenuation. Any depolarization value is related to a corresponding attenuation by the following rule : to a particular attenuation corresponds a worst depolarization (horizontal link, circular polarization) depending on the frequency and local climatic conditions; this relation can be experimentally determined. To this are added (in decibels) a depolarization improvement which is a function only of the elevation angle and, for a linear polarization, a second improvement which is a function only of the polarization angle.     

光声方法测量粘弹介质声衰减的研究

衰减是材料的一项重要参数,测量衰减将有助于评估材料的空隙率、微观裂纹分布、颗粒尺度、材料强度及软体组织结构等。该文利用光声手段对介质的表面波衰减进行了测量研究。由激光激发表面波,换能器检测。对连续采样所获得的表面波信号进行加窗、滤波、FFT处理及相干分析,得出介质衰减与频率的关系。实验结果表明,利用光声手段及表面波方法是对固体材料衰减测量的有效手段之一。     

The role of rain in satellite communications

The most fundamental obstacle encountered in design of satellite communication systems at frequencies above 10 GHz is attenuation by rain. The microwave power radiated toward an earth station, being limited by factors such as available primary power and size of antenna on the satellite, is insufficient, with present technology, to overcome the large attenuation produced by intense rain cells on the earth-space path. The resultant loss of signal makes for unreliable transmission. In what follows, methods of measurement of this attenuation at various frequencies and a technique called path diversity that substantially improves the reliability are presented. Other degradations produced by rain, such as depolarization, interference, increase in earth-station noise, and deterioration of earth-station antenna performance, are also discussed.     

A Radiometric Method for Measuring the Insertion Loss of Radome Materials

Though radomes have been used for years as a means of protecting antennas from the elements, little appears in the Iiterature to aid the engineer in his choice of the radome material to use in a particular installation. This may be due to the fact that many radome materials are adequate when used with a receiving system having a mixer (i.e., relatively hot) front end. However, an improper choice of radome material can seriously degrade a receiving system that employs a maser or other low-noise front end. A radiometric technique for the measurement of insertion loss is described, and a sample calculation, including error analysis, is presented.