This paper presents a new power-sharing multiple-beam mobile satellite system concept in the Ka band. A wide allocated bandwidth and a large amount of frequency reuse based on hundreds to thousands of small spot beams will allow us to draw a drastically new mobile satellite systems concept in the Ka band. At first, requirements for beam size on the surface of the Earth for various signal transmissions are considered. Based on these requirements, Ka band geostationary systems with 3.5 and 10 m satellite antennas are shown. If the number of beams is hundreds to thousands, it is not appropriate to assume a fixed power transmitter for each beam because the traffic in each beam is not uniform or static. In order to cope with this multiple-beam-varying traffic problem, this paper proposes a new type offset reflector antenna fed through an equal phase-shift active array. The proposed active array consists of hundreds to thousands of equal phase-shift elements. Features and simulated performances of the proposed transmitting antenna are presented. Preliminary experimental results from a 2.1 m reflector fed through 332 hollow elements are also shown. Since each beam commonly utilizes all active array elements, power sharing among beams is possible, allowing traffic variation among beams without loss of power efficiency.

An adaptive multiple beam system, which has flexibility to adapt beam power to varying beam traffic, is proposed. The multiple beam transmitter, which is called "hybrid transponder" in this paper, consists of a pair of multiport hybrids and a set of amplifying elements. Power combining, isolation, and intermodulation characteristics of this multiport network are analyzed. Also, a new interbeam exchange and feeder link connection concept, which serves as the basis for an adaptive multiple beam system, is proposed. Finally, characteristics of an experimental 8-amplifier 8-port hybrid transponder are described.

A simple and effective means to cope with the rain attenuation inK-band FDMA satellite communications is described. To optimize satellite transmitting power for each FDMA carrier, received satellite link quality level sent back to the transmitting Earth station is used.

Design considerations of aK-band (30/20 GHz) mobile earth station for a domestic satellite communications system are described. A Japanese Medium Capacity Communication Satellite which utilizesKandCsatellite communication bands was considered for the system design. Transmitting power control method, statistical link quality estimation, and equipment description are given.