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.

An algorithm that detects the surface echo peak position in a radar echo range profile has been developed for the TRMM Precipitation Radar (PR). The purpose of the surface echo peak detection is to determine the range window in which "over-sample" data are collected. The surface echo position in the range profile is variable due to the systematic change of satellite geodetic altitude and surface topography. The dynamic control of the over-sample range window using the surface detection algorithm contributes significantly to the reduction of PR data rate that should be sent to the ground station. The algorithm employs an α-β tracking filter and has three functions; surface tracking, lock-off detection and tracking loop initialization. After the launch of the TRMM satellite, a series of initial check-out of the PR was conducted. The performance of the algorithm was evaluated through the initial check-out and two-years operation of the PR. The results indicate that the algorithm is working as expected and basically meets the specification; however, it is found that some functions such as the tracking loop initialization algorithm need to be improved.

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.

An experimental study on propagation characteristics in a room of a modern office building using a 57.5 GHz carrier is described. The objective of the study is to provide initial information about the path-loss and fading characteristics for millimeter-wave wireless indoor communication systems. The area of the floor of the room is about 90 m2 and the room was almost empty with no furniture except the experimental apparatus. A wide-beam scalar feed horn transmission antenna and an omnidirectional receiving antenna were used and set to be with the same height. The measured area was divided into many "squares" to characterize the propagation. The variation of square transmission loss was calculated, and the regions where the maximum square transmission loss was observed were pointed out. It became clear that the distance power law for square transmission loss was approximately of the order d-2 along the direct path. Rician distributions for fast fading were derived in almost all squares of this room. The spectra for the fast fading envelope were also derived. From the propagation point of view, the results show that no extreme difficulty seems to exist in developing wireless communication systems in the 60 GHz band.

An airborne X- and L-band synthetic aperture radar system was developed by the Communications Research Laboratory and the National Space Development Agency of Japan in their joint project from 1993 to 1996. It is installed in the airplane, Gulfstream II. In both the azimuth and range directions, the resolution is 1.5 m for the X-band and 3 m for the L-band. Both SARs can make fully polarimetric observations. The X-band SAR has a cross-track interferometric function. In this paper we describe the SAR system, its ground processing system, and its performance. We also discuss motion compensation and interferogram quality.

A phase-retrieval method is applied to the quasioptical feed system of the offset Cassegrain antenna of the Superconducting Submillimeter-Wave Limb-Emission Sounder (JEM/SMILES) to be aboard the International Space Station for evaluating the beam alignment by estimating the phase pattern from the beam amplitude pattern measurements. As the result, the application of the phase retrieval method is demonstrated to be effective for measuring and evaluating the quasioptical antenna feed system. It is also demonstrated that the far-field radiation pattern of the antenna main reflector can be estimated from the phase-retrieved beam pattern of the feed system.

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.

This paper mainly concentrates on recent studies on land mobile propagation, considering new trends of the progress of digital and personal land mobile communications. High speed digital transmission for millimeter-wave indoor communication is of another current interest. Microcellular propagation in urban areas and indoor propagation are major research targets at present days. Multipath propagation characteristics such as delay-profiles becomes more and more important measuring items, and some signal processing methods like MUSIC method have been widely introduced to improve the time resolution against the limit of available radio bandwidth. Path-loss characteristics in mobile propagation are extended to the path-loss prediction and are going to be applied to cellular system design in connection with the design of directional base-station antennas. Another recent topic is an extension of target frequency bands for mobile propagation studies, which are spreading from VHP, UHF and SHF to EHF bands.