Noboru Toyama

Aperiodic array consisting of subarrays for use in small mobile Earth stations

A simple yet practical method of designing an aperiodic array consisting of subarrays is shown. By properly controlling the excitation phase of each subarray, the designed aperiodic array has the capability to track a geostationary satellite within some limited angles. Starting with an initial position of the subarrays, their optimum positions in terms of the side lobe performance can be obtained by a newly developed algorithm which uses the steepest descent method together with an appropriately defined cost function. An example of an aperiodic array consisting of 16 subarrays in the 14 GHz band is shown. It can track a geostationary satellite at the maximum of 2/spl deg/ off its mechanical boresight (the direction perpendicular to the surface of the array). Although it is nearly square with the maximum dimension of only 47/spl lambda/ (wavelength), its calculated side lobe patterns satisfy most of the requirements specified in the International Telecommunication Union (ITU) recommendations, which must be met by all earth stations with antennas of larger than 50/spl lambda/ in diameter.

Single shaped reflector antennas for broadcasting satellites

For future direct broadcasting satellites in Japan, precisely contoured beam antennas will be required for onboard antennas. Single shaped-reflector antennas are suitable for that purpose, since they do not need complex feed networks. However, in a previous study, discontinuities in the reflector surface were observed. The problem of the discontinuity was circumvented in this work and the shaped reflectors were successfully designed to produce contoured beams for covering the Japanese islands for the downlink and feederlink antennas. The downlink antenna was fabricated, and the radiation pattern was verified by measurement. The radiation pattern meets the radio regulations imposed on the onboard antenna, such as sidelobe and cross-polarization characteristics. >

Hardware performance and experimental results of portable digital SNG equipment using a flat antenna

We have developed a Ku-band portable digital satellite news gathering (SNG) RF terminal and evaluated the hardware performance through experiments. This SNG RF terminal employs a 16-planar microstrip subarray antenna and an electronic antenna beam tracking circuit. The dimensions for the flat antenna are 60 cm by 60 cm. The terminal can promptly capture the satellite and transmit the video at 15-Mbps, 11-Mbps, and 7-Mbps coding rates. After satellite transmission experiments, we confirmed the stable transmission of a QPSK signal. This paper first describes the system configuration. It then shows the experimental results of the hardware performance such as antenna beam tracking performance and the radiation patterns. Finally, it shows the results of satellite transmission experiments of TV pictures. From these experimental results it is verified that (1) within the tilt angle of /spl plusmn/3 degrees, the off axis e.i.r.p. density level of the terminal is less than the technical standard specified in the ITU-R Recommendation 524; and (2) the SNG stably transmits TV programs and has a sufficient C/N margin of about 3 dB, 5 dB or 7 dB for the respective video coding rates of 15 Mbps, 11 Mbps, and 7 Mbps.

A study of a contoured beam antenna for future Japanese DBS

This paper describes a study of contoured beam onboard a n t e n n a for f u t u r e Japanese direct broadcasting satellites (DBS) with pattern analysis and test results for the full-scale bread board model (BBM). The BS-3a and BS-3b were launched in 1990 and 1991, respectively, by the HI launch vehicle into a geo-synchronous orbit of 110 degrees east longitude. A follow-on DBS will be launched before the end of the BS-3s life (7 years). As the methods to realize the contoured-beam pattern for Japanese territory, the BS-3 antenna employs an elliptical offset parabolic reflector fed with a new type. \rJ of elliptical corrugated horn as well as a rectanylar horn. Thus, the contoured beam is based on an el ipse, and it is difficult to achieve the best fitting contour patterns for the Japanese territory. The antenna examined herein consists of a shaped reflector and a horn. This shaped reflector antenna has achieved a better shaped radiation pattern than the BS-3, and has attained a gain of more than 38 dBi for the major parts of Japan while, maintaining the RR.AP30* regulations for sidelobe and cross-polarization levels, theoretically and experimentally. In order to verify our shaped reflector antenna characteristic, a BBM antenna with 2.3m aperture was constructed and has shown good agreement with the analytical results. The authors propose this reflector antenna as a candidate for the next Japanese direct broadcasting satellite antenna system.