Yoji Furuhama

The relationship of raindrop-size distribution to attenuations experience at 50, 80, 140, and 240 GHz

Millimeter-wave rain attenuation measurements have been made at 50.4, 81.8, 140.7, and 245.5 GHz on a terrestrial path of 0.81 km. On the basis of these experimental results, a comparison between the model of specific attenuation currently adopted by the International Radio Consultative Committee (CCIR) and that based on the raindrop-size distribution derived from our previous propagation experiments at 11.5, 34.5, and 81.8 GHz is made. For the Japanese climate, it is found that the CCIR model underestimates the rain attenuation at frequencies above 80 GHz and that our specific attenuation model is effective for the prediction of rain attenuation in the whole millimeter-wave region.

Propagation Measurements and Tv-Reception Tests With the Japanese Broadcasting Satellite for Experimental Purposes

In July 1978, stationary experiments were commenced with the Japanese Medium-Scale Broadcasting Stellite for Experimental Purposes (BSE). In this BSE project, frequencies of 14/12 GHz are applied to the up and down links, respectively, and experiments have been carried out from the points of propagation and receiving. The analys is of the propagation measurements revealed statistics of rain attenuation in various parts of Japan. By the TV-reception tests, it has been confirmed that received power was generally coincided with the predicted one and received picture was excellent at each receiving location which was distributed all over Japan.

Measurments of attenuation and refractive dispersion due to atmospheric water vapor at 80 and 240 GHz

Field line-of-sight propagation experiments were made at 80 and 240 GHz on a horizontal path of 810 m. The measured attenuations showed quadratic dependences on atmospheric water vapor density, and absorptions in excess of theoretical predictions were observed at both frequencies, while the measured refractive dispersion between these two frequencies showed a linear dependence on water vapor density and was in good agreement with theoretical prediction. Liebes model for water vapor attenuation including empirical continuum absorption is confirmed to be effective for 80 and 240 GHz.

ETS-II Experiments Part IV: Characteristics of Millimeter and Centimeter Wavelength Propagation

Preliminary results of the ETS-II millimeter and centimeter wavelength propagation experiments are presented based on data collected over one year. Rain attenuation is discussed primarily from the statistical point of view. At 34.5 GHz attenuation in excess of 5, 10, and 19.5 dB were observed 1, 0.3, and 0.1 percent of the test time (5500 hr), respectively. At 11.5 GHz attenuation in excess of 2.5, 4.3, 6.3, 10, and 15.5 dB were observed 0.1, 0.03, 0.01, 0.003, and 0.001 percent of the test time, respectively. Duration time of attenuation is also examined for the benefit of a link design. The longest duration of attenuation of the 34.5-GHz wave exceeding 5 dB was about 150 min. At 11.5 GHz, the longest duration of attenuation in excess of 3 dB, was 60 min and that in excess of 6 dB was 10 min. Rain attenuation is discussed also with relation to the radar and the rain gauge data. Depolarization data of 34.5-GHz and 11.5-GHz waves are orocessed statistically, and it is shown that cross-polarization discriminations in excess of 21.5 dB and 29 dB are observed 0.1 percent of the test time at 34.5 GHz and 11.5 GHz, respectively.

Propagation characteristics of millimetre and centimetre waves of ETS-II classified by rainfall types

A propagation experiment at the frequencies of 1.7, 11.5 and 34.5 GHz using Engineering Test Satellite Type IIEts-II was conducted at the Kashima earth station of the Radio Research Laboratories (Rrl).Several meteorological parameters were also measured simultaneously at the station using rain gauge networks, a C-band rain radar, a 35 GHz radiometer and meteorological instruments.The whole data for one year in this experiment were classified into three rain types such as stratus, cumulusand others by using radar data along the path mainly to determine the size of precipitation area and whether the radar bright band existed or not.Rainfall classified as stratus occurred for 45 % of the total rainfall time, whilst rainfall classified as cumulus occurred for 10 %, and others for 45 % of the total rainfall time. For the co-polar attenuation, a prediction method based upon an assumption of spatial homogeneity is found to be applicable to the Earth-space path for the stratus type, though the method is not applicable for the cumulus type. On the contrary, in the degradation ofXpd,a prediction method based upon an assumption of deformed raindrops is not applicable to the path for the stratustype, while the method is applicable for the cumulus type.AnalyseUne expérience de propagation à des fréquences de 1.7, 11.5 et 34.5 GHz utilisant le satelliteEts-II a été réalisée à la station de Kashima du Radio Research Laboratories. Quelques paramètres météorologiques ont simultanément été mesurés à la station, à l’aide de pluviomètres, d’un radar météorologique dans la bande C, d’un radiomètre à 35 GHz et de divers instruments météorologiques. Tous les résultats de l’expérience pour une année ont été classés suivant trois types de précipitations: stratus, cumuluset autres cas;ceci, grâce aux enregistrements du radar qui ont permis de déterminer l’aire couverte par la précipitation et l’existence ou non-existence de la bande brillante du radar. L’occurrence de précipitations du type stratus est observée durant 45% de la durée totale de précipitation, le type cumulusdurant 10% et le type autres cas45%. On trouve pour l’atténuation copolaire une méthode de prévision basée sur l’hypothèse d’homogénéité spatiale qui est utilisable sur un trajet Terre-espace pour une précipitation du type stratus mais ne l’est pas pour le cas cumulus.Par contre, pour la dégradation du découplage de polarisation croisée, une méthode de prévision supposant les gouttes déformées n’est pas applicable au type stratusmais l’est au type cumulus.

Inference of raindrop size distribution from attenuation and rain rate measurements

A method to infer the raindrop size distribution from the measurements of point rain rate and rain attenuation at a frequency in centimeter or millimeter wave bands is proposed. This method is applied to the results of field propagation experiments at 81.8, 34.5, and 11.5 GHz through natural rain. It is shown that, if an appropriate frequency is employed, this method is effective as a frequency-scaling method for short terrestrial propagation paths.

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

The attenuation of 245.52 GHz millimeter wave was measured through a near ground horizontal path in order to study the anomalous water vapor absorption at the window region. The result demonstrates that the attenuation coefficient includes the quadratic dependence on the water vapor density. The quadratic component of the water vapor density in the expression of the attenuation was assumed to arises from the contribution of water dimers alone, then the concentration of water dimers was estimated adopting the published theoretical water dimers absorption coefficient. The obtained concentration was 0.062% of monomers in number when the water vapor density is 7.5 g/m3. This concentration is in agreement with the published result obtained by way of another method.

Recent propagation studies in Japan

Reviews activities in the field of propagation research, in the 1990s, in Japan. The authors focus only on propagation studies related to radio communications; activities in the field of remote sensing are outside the scope of this review. Since Kagoshima and Shiokawa (1992) included a short review of research activities in this field, in the period from 1989 to 1991, the emphasis of the present review is placed on activities after this period. The list of references consists of only papers written in English, which have appeared in international journals or published proceedings of international conferences. Reflecting the activities of various fields of propagation research in Japan, two-thirds of the review is devoted to propagation studies related to mobile communications, including land-mobile, mobile-satellite, and indoor communications. The rest of the review covers other basic studies, related to propagation through the atmosphere and precipitation.<<ETX>>

Spatial correlation coefficients of rainfall intensity inferred from statistics of rainfall intensity and rain attenuation

On the basis of the reliable statistics of rainfall rate and rainfall attenuation for 8 localities in Europe, the spatial correlation coefficient of point rainfall intensity was inferred for each locality from the cumulative distributions of attenuation and rainfall intensity by inversely applying the modified Morita and Higuti rainfall attenuation prediction method. It was found that for European regions the spatial correlation coefficient with an exponential dependence on the horizontal distance is more appropriate for the prediction of rainfall attenuation than that proposed by Morita and Higuti for the Japanese climate. It was also found that although the spatial correlation characteristic varies significantly from one locality to another its variance is not so significant within a particular ccir rainfall climatic zone. This suggests that in predicting the rainfall attenuation it is desirable to employ the spatial correlation coefficient appropriate for the locality to be estimated.AnalyseSur la base de statistiques fiables des intensités de précipitation et des affaiblissements dus à la pluie, pour huit localités d’Europe, on a établi les coefficients de corrélation spatiale des intensités de précipitation locales. Ces coefficients ont été obtenus, pour chacune des localités, à partir des distributions cumulées des affaiblissements et des intensités de précipitation, en appliquant de façon inverse la méthode modifiée de prévision des affaiblissements dus à la pluie de Morita et Higuti. Ces résultats montrent que pour les régions d’Europe, un coefficient de corrélation spatiale qui est fonction exponentielle de la distance horizontale est mieux approprié à la prédiction des affaiblissements dus à la pluie que celui proposé par Morita et Higuti pour le climat japonais. Bien que la corrélation spatiale caractéristique varie de manière significative d’une localité à une autre, sa variation n’est pas très importante à l’intérieur d’une zone climatique de précipitation définie par le ccir. En matière de prédiction des affaiblissements dus aux précipitations, il est donc préférable d’employer le coefficient de corrélation spatiale approprié à la localité où a lieu l’estimation.

Propagation characteristics for millimeter and quasi-millimeter waves by using three Japanese geostationary satellites

Abstract Propagation experiments using the following geostationary satellites, Engineering Test Satellite-II (ETS-II), Medium-Capacity Communication Satellite for Experimental Purposes (CS), Medium-Scale Broadcasting Satellite for Experimental Purposes (BSE) and Experimental Communication Satellite (ECS), are being conducted by Radio Research Laboratories (RRL) with the co-operation of National Space Development Agency of Japan (NASDA), Nippon Telegraph and Telephone Public Corporations (NNT) and Japan Broadcasting Corporations (NHK). The Experimental Communication Satellite (ECS) will be launched into the geostationary orbit in February 1980. This satellite will then be used for further propagation experiments. The various and numerous propagation data obtained by using these satellites is being collected from many places all over Japan. The summary of the propagation experiments conducted at the main station is as follows. 1. (a) Experimental periods covered in this paper are about 1 year for ETS-II and CS, and six months for BSE. 2. (b) The percentages of time in which measured attenuation exceed 5, 10 and 15 dB are 0.7, 0.3 and 0.15% respectively at 34.5 GHz (ETS-II), 0.08, 0.016 and 0.008% respectively at 19.45 GHz (CS), 0.025, 0.0025 and 0.0009% respectively at 11.7125 GHz (BSE), and 0.02, 0.0023 and 0.001% respectively at 11.5 GHz (ETS-II). 3. (c) Duration of attenuation exceeding 30 dB at 34.5 GHz is less than 50 min with the occurrence probability of 0.013% for a one year period. Attenuation exceeding 6 dB at 11.5 GHz and the one exceeding 10 dB at 19.45 GHz are 0.0025% (8 min in a year) and 0.015% (10 min in three months). 4. (d) In the cumulative distributions of XPD (Cross Polarization Discrimination), values of XPD exceeding the percentages of time, 0.3, 0.1, 0.03 and 0.01% are 25, 22, 19 and 17 dB respectively at 34.5 GHz, 28, 23, 20 and 16.5 dB respectively at 19.45 GHz and 33, 29, 26 and 24 dB respectively at 11.5 GHz. This paper presents an outline of the propagation experiments carried out by using ETS-II, CS, BS and ECS, and propagation characteristics of radio waves mainly above 10 GHz at the main station (Kashima Branch, RRL).