Engineering topics

Hase, Yoshihiro

Publications and source records attributed to Hase, Yoshihiro.

6 records

NASA NTRS1995

Propagation experiment of COMETS Ka/Q-band communication link for future satellite cellular system

Mobile/Personal Satellite Communication Systems in L/S-bands are going into the operational phase. In the future, they will be operated in much higher frequency bands, for example in Ka-band, because the available bandwidth in L-band is limited. Systems with large on-board antennas in higher frequencies allow the same configuration as terrestrial cellular radio systems, since the on-board antennas will have many small spot beams. This may be true especially in a low earth orbit system such as Teledesic, which will use Ka-band. The most important parameter of Satellite Cellular may be cell size, that is, a diameter of the spot beam. A system designer needs the local correlation data in a cell and the size of the correlative area. On the other hand, the most significant difficulty of Ka and higher band systems is the countermeasure to rain attenuation. Many-cell systems can manage the limited power of on-board transponders by controlling output power of each beam depending on the rain attenuation of each cell. If the cell size is equal to the correlative area, the system can probably achieve the maximum performance. Propagation data of Ka and higher band obtained in the past shows a long term cumulative feature and link availability, but do not indicate the correlative area. The Japanese COMETS satellite, which will be launched in February 1997, has transponders in Ka and Q-band. The CRL is planning to measure the correlative area using 21 GHz and 44 GHz CW transmissions from the COMETS.

Hase, Yoshihiro↗

NASA NTRS1995

Mobile antennas for COMETS advanced mobile Satcom experiment

Advanced mobile satellite communication experiments in the Ka-band and the mm-wave will be carried out using the COMETS satellite, which is scheduled for launch in 1997. Mobile antennas will play a much more key role in high frequency systems such as COMETS than in conventional L-band mobile systems. This paper describes three types of antennas which are now being developed by the Communications Research Laboratory (CRL) for the COMETS mobile experiments. One is a mechanically steered waveguide slot array antenna, another is an electronically steered active phased array antenna, and the third is a mechanically steered torus reflector antenna. The first two antennas will be used in the Ka-band, while the latter will be used in the mm-wave.

Hase, Yoshihiro↗

NASA NTRS1992

Land-mobile-satellite fade measurements in Australia

Attenuation measurements were implemented at L-band (1.5 GHz) in southeastern Australia during an 11-day period in October 1988 as part of a continuing examination of the propagation effects due to roadside trees and terrain for mobile-satellite service. Beacon transmissions from the geostationary ETS-V and IPORS satellites were observed. The Australian campaign expanded to another continent our Mobile Satellite Service data base of measurements executed in the eastern and southwestern United States regions. An empirical fade distribution model based on U.S. data predicted the Australian results with errors generally less than 1 dB in the 1-20 percent probability region. Directive antennas are shown to suffer deeper fades under severe shadowing conditions (3 dB excess at 4 percent), the equal-probability isolation between co- and cross-polarized transmissions deteriorated to 10 dB at the 5 dB fade level, and antenna diversity reception may reduce unavailability of the system by a factor of 2-8.

Vogel, Wolfhard J.↗

NASA NTRS1991

Fade-durations derived from land-mobile-satellite measurements in Australia

Transmissions from the Japanese ETS-V geostationary satellite were measured at L band (1.5 GHz) in a vehicle driving on roads of southeastern Australia. The measurements were part of a program designed to characterize propagation effects due to roadside trees and terrain for mobile satellite service. It is shown that the cumulative distributions of fade and nonfade durations follow a lognormal and power law, respectively. At 1 percent probability, fades last 2-8 m, and nonfades 10-100 m, depending on the degree of shadowing. Phase fluctuations are generally small, allowing the channel characteristics to be estimated from levels only.

Hase, Yoshihiro↗

NASA NTRS1990

Satellite sound broadcast research aspect in CRL

Researches on Satellite Sound Broadcasting Services (SSBS) have become active in the past few years. Activities of the Consultative Committee for International Radio (CCIR) and the World Administrative Radio Conference (WARC), especially about digital systems proposed in the CCIR report, are briefly reviewed. The Communications Research Laboratory (CRL) future plan of SSBS research, stressing propagation rather than communications aspects, is described.

Hase, Yoshihiro↗

NASA NTRS1989

The Australian experiment with ETS-V

Land-mobile satellite propagation measurements were implemented at L Band (1.5 GHz) in South-Eastern Australia during an 11 day period in October 1988. Transmissions (CW) from both the Japanese ETS-5 and INMARSAT Pacific geostationary satellites were accessed. Previous measurements in this series were performed at both L Band (1.5 GHz) and UHF (870 MHz) in Central Maryland, North-Central Colorado, and the southern United States. The objectives of the Australian campaign were to expand the data base acquired in the U.S. to another continent, to validate a U.S. derived empirical model for estimating the fade distribution, to establish the effects of directive antennas, to assess the isolation between co- and cross-polarized transmissions, to derive estimates of fade as well as non-fade durations, and to evaluate diversity reception. All these objectives were met.

Vogel, Wolfhard J.↗