Frequency scaling method, employing the concept of path-averaged raindrop size distribution (D), is successfully applied to predicting the rain attenuation statistics. Experimentally determined Eq. (D)26,000-0.294 exp (-5.6-0.283D), (: a path-averaged, rainfall rate) is applicable to the prediction even in the frequency above 80 GHz where Laws and Parsons distribution falls into underestimation.

The worst month statistics of rain attenuation at 34.5 and 81.8 GHz along a terrestrial path of 1.3 km and rain rate were analyzed. The relation between the worst month percentage and the yearly percentage is independent of frequency. The results we obtained on the worst month statistics show a good agreement with Brussaard and Watson's semi-empirical model.

A depolarization phenomenon at 34.5 GHz due to wet snow was observed in a horizantal terrestrial path of 1.3 km. Data during snowfall show fairly large degradations of XPD in comparison with data during rain and theoretical values based upon the model of deformed raindrop, under the condition of the same copolar attenuation. Much larger deformation of snowflake than that of raindrop must be assumed to explain such inclination by the model of depolarization due to an oblate spheroidal snowflake. Effective differential propagation constants of snow, which are derived from measurements of XPD and phase difference between cross- and co-polar components, show that depolarization due to wet snow at 34.5 GHz comes from not only differential phase shift but also differential attenuation. A certain kind of anomalous depolarization on Earth-space paths may be explained by the model of depolarization due to wet snow.

A path-averaged raindrop size distribution is inferred from the equi-probability values of cumulative distribution of rain attenuation measured at 11.5, 34.5, and 81.8 GHz on the same propagation path of 1.3 km in a suburb of Tokyo for three years. By using the size distribution, attenuation coefficients due to rain are obtained in the frequency range from 10 to 300 GHz. The same kind of examination has already been made on the basis of the first one-year data. However, the result obtained this time is slightly stable in comparison with the result for the one-year data in statistical meaning, and is usable for predicting the rain attenuation at frequencies up to about 100 GHz with high accuracy. Moreover, the raindrop size distribution of Laws and Parsons is found to lead to an underestimation of rain attenuation by 30 or 40 percent in dB value at rain rate of 10 to 50 mm/h in the frequency range above about 100 GHz.

In the Morita and Higuti (M-H) attenuation prediction method, the spatial correlation function of specific attenuation for conditional time, ρΓ, is, approximated by ρ, the spatial correlation function of rainfall rate. The accuracy of this approximation is examined in this paper. An equation relating ρΓ to ρ is theoretically derived assuming a bi-lognormal distribution of rainfall rates at two points. Theoretical examination shows that the approximation ρΓ=ρ does not necessarily hold accurately in the frequency range 10 to 100 GHz, except for frequencies near 30 GHz. This is also confirmed experimentally by measurements from a rain gauge network. A modified M-H method in which attenuation is predicted using ρΓ is proposed, and an extensive numerical comparison between both methods is made. It is shown that the approximation ρΓ=ρ can limit the applicability of the M-H method in terms of rain climatic condition, frequency, and path length, and that the modified M-H method has the advantage of improved applicability, compared with the M-H method.

This paper presents a novel four-sector shaped-beam antenna suitable for base station antennas in 60-GHz wireless local area networks (LANs). The antenna has a plateau configuration, whose four side walls have four linearly arranged microstrip antennas. Each trapezoidal facet excites a shaped beam in the elevation plane in order to meet link-budget requirement between base station and remote terminal, taking account of directional patters of remote terminal antennas. Low-loss curved microstrip-line is applied to connect the three-dimensional antennas with active circuits mounted on a flat carrier plate. This antenna has been adopted as the base station antenna in 60-GHz wireless LANs. The first-stage transmission experiment confirms the usefulness of shaped-beam antennas in the 60-GHz band.

In this paper, an experimental result of complex refractive index of soda-lime glass at 30-GHz obtained by transmission method is presented at first. Secondly, a simple empirical formula of complex refractive index of soda-lime glass over frequency range from 0.1-GHz to 1000-GHz is derived using the present experimental result together with data previously reported in literatures by various researchers.

This paper proposes an asymptotic method for calculating the received intensity of multi-path millimeter waves transmitted over an undulating surface. This method is a generalization of the asymptotic method that the authors previously derived, based on a quartic phase function approximation, from the physical optics integral expression of the received intensity. The applicability of the previous method is limited to ratios of transmission distance (D) to surface undulation wavelength (λs) of roughly less than 2. This is because the method is based on a quartic phase function approximation. In this paper, this limitation is resolved through this method's generalization, which is achieved by incorporating a technique for calculating the diffraction integral with a higher-degree phase function by using the steepest descent technique with a procedure for systematically identifying the active saddles of the phase function. Numerical examples demonstrate that the proposed asymptotic method can attain calculation accuracy comparable with the physical optics method, even in the case of large D/λs values.

This paper presents the initial results of a study of an asymptotic method for calculating the received intensity of multi-path millimeter waves transmitted over an undulating surface. First, an integral expression of the received intensity is derived using a physical optics approximation. Then its zero-th order asymptotic expression is derived, using the Pearcey integral, for the case where the phase function appearing in the integrand can be approximated by a quartic polynomial. A numerical examination made at 59.5 GHz showed that the asymptotic method is in good agreement with the physical optics method, even in cases where the geometrical optics method deviates significantly from the physical optics method, and that the range of applicability of the asymptotic method has its upper bound somewhere around a transmission distance to surface undulation wavelength ratio of 2.

Profiles of radar Z-factor are presented which are obtained from the C-band radar along the path Kashima to the ETS- satellite during May 1977 to April 1978. The whole data are classified into three rainfall types of the stratus, the cumulus, and the others, where the time percentages for these types are 45, 10, and 45, respectively. There exists a characteristics difference between the stratus and the cumulus with respect to the profile.

This paper gives an overview of the research and development trends in millimeter-wave short-range application systems, such as communication systems and sensing systems, in Japan and other countries. Frequency management trends are also described. Major research and development efforts in Japan have currently been concentrated on the 59-64 GHz band. The first major achievement resulting from those efforts was the allocation of the 60-61 GHz band to the automotive radar systems. Test productions of automotive radars in this band have already started. Further technological developments to reduce the cost and size of radar products are, however, required in order for such radar systems to be widely used. Development of broadband wireless LAN systems has also been intensively made in the 60 GHz band. In addition, technical issues related to standardization of millimeter-wave wireless LAN systems in the 60 GHz band have been examined at the Association of Radio Industries and Businesses. The application areas of millimeter-waves in the future are expected to become more diverse. Research and development trends of future application systems, such as broadband mobile communication systems and imaging radar systems, are also described. These systems require more advanced millimeter-wave technologies, such as smart antennas, low power-consumption devices, and more sensitive detectors. Efforts to develop these technologies must be strengthened.

As a result of examination based on a newly available data set of millimeter-wave rain attenuation measured in the UK, it is found that the ITU-R specific rain attenuation model tends to appreciably underestimate millimeter-wave rain attenuation at frequencies above about 60GHz for the UK rain climate. This tendency is very similar to that previously reported for the Japanese experimental data at frequencies up to 245GHz. Furthermore, an alternative specific rain attenuation model based on the Japanese experimental data is found to be in fairly good agreement with the experimental data in the UK at frequencies up to 137GHz.

It was experimentally verified that the rain attenuation at 140 GHz depends not only on the rain rate but also appreciably on the raindrop size distribution. The size distributions inferred from the attenuation and the rain rate measurements show excellent agreements with those measured by the filter paper method.