System design and operational results of a tracking system for a K-band Earth station antenna with a diameter of 11.5 m are discussed. Monopulse tracking technique using higher order waveguide modes is utilized. An investigation was conducted to clarify the rainfall effect and the effect of oscillator phase noise on the tracking receiver. An autotrack system is to be manufactured on the basis of these studies. Experiments were performed using the medium capacity communications satellite. No cross coupling was seen in the pull-in patterns. Sufficiently good results were obtained in tracking accuracy: less than 0.005° (peak value) under normal conditions, and less than 0.01° under an average wind velocity of more than 20 m/s.

K-Band Tracking System for Domestic Satellite Communication System

This paper presents the results of a study to determine the satellite capacity enhancement obtainable by using syllabic compandors. Syllabic companding applied to the speech channels of tDDM-rm carriers can increase satellite capacity by as much as 100 percent, depending on the number of channels per carrier. Syllabic compandors presently produced by integrated circuit technology are small and inexpensive. Compandors permit a higher level of satellite circuit noise and hence an FM index (and bandwidth) which is smaller than that required for uncompanded channels. The results presented in the paper are based on compandor advantage measurements and singleand multi-channel amplitude distribution measurements for both companded and uncompanded speech signals. For data transmission, it is estimated that about 2-dB degradation may be encountered when long terrestrial access circuits are interconnected via a companded satellite circuit for international transmission. *This paper is based upon work performed at COMSAT Laboratories under the sponsorship of the International Telecommunications Satellite Organization (INTELSA r).

Enhancement of FDM-FM satellite capacity by use of compandors

IEEE Transactions on Communications Special Issue on Picture Communication Systems

Optimum beam scanning in offset single reflector (paraboloid) and dual reflector (Cassegrain and Gregorian) antennas is considered. Analytical, computationally efficient solutions and results are presented for the optimum feed position, the constant beam direction feed loci, and the optimum feed position locus. Examples are presented to verify that the analysis technique yields the optimum feed position, which exhibits better gain, pattern symmetry, and sidelobe levels when compared with other feed positions producing beams scanned to the same direction. The solutions described were obtained under the ray optics approximation and a "receive mode" analysis. Although the developed method was applied to the antennas listed above, it can be easily extended to other n -reflector systems, shaped reflector antennas, lenses, and other similar systems.

Optimum beam scanning in offset single and dual reflector antennas

Recent microwave antenna technologies which are developed in Japan are reviewed. Main antennas which are practically used in various fields are described. The trends of antenna research works are also shown.

Microwave Antenna Technology

Offset reflector antennas have advantages for communication systems because they are not severely subject to blocking. Difficulties mainly arising from structual asymmetries have inhibited the realization of an offset reflector antenna with a large aperture for commercial use. This paper describes the design of an offset Cassegrain earth station antenna for the Japanese domestic satellite communication system. Antenna measurements showed 76 and 69 percent aperture efficiencies at 20 and 30 GHz, respectively, less than -20 dBi wide angle directivity and an 18 K noise temperature in operating conditions. Performances are far superior to conventional axisymmetrical earth station antennas. The antenna was reassembled on a telephone office building after the measurements. The antenna gain was reconfirmed there, using the sun as a radio frequency source. Experiments show that the earth station antenna and a terrestrial antenna can be placed on the same building without serious interference.

M. Shinji

Papers

Offset Cassegrain Earth Station Antenna for the Japanese Domestic Satellite Communication System