SMALL SATELLITE COMMUNICATIONS TERMINALS

Introduction

Earth stations or terminals have undergone a steady evolution towards smaller size. The numbers employed in systems have steadily increased as the sizes reduced. The last decade has seen the rapid deployment of thousands of very small aperture terminals (VSATs). These terminals employ antennas of 0.6 m to 2 m diameter. Thousands of these small terminals are used in business data communications applications and provide the advantage of "customer premises" location and ability to bypass PSTN for cost savings. At present, these systems are experiencing a rapid growth in Europe, especially in eastern Europe, where the telecommunications infrastructure was either outmoded or non-existent.

VSATs employ monolithic microwave integrated circuits to miniaturize the RF parts, especially the receiver. Such components literally enable such terminals as TV receive-only (TVRO) stations for television broadcast, another application that continues to witness a proliferation of terminals throughout Europe.

For some applications, a new technology, such as an ultra-lightweight mesh reflector, makes a viable product possible. In most cases, however, VSAT antennas involve the same or similar technology used in many terminals of larger size in the past. Antenna technology and special purpose MMICs and integrated circuits are the important technologies -- e.g., very large scale integration and applications specific integrated circuits (ASICs). General progress on these technologies is not dependent on a need for VSATs and is also stimulated by applications in satellites, radar and consumer products.

European Activities

There was no extensive evidence of R&D in technologies or new products for VSATs. Several agencies such as the FTZ have been active and have enjoyed success in marketing products or transferring technology. The sudden market needs in Eastern Europe provide an opportunity in this area. Ability to deploy terminals rapidly to establish a network is a major in these new markets. In addition, the emergence of broadcast satellite television represents a large market opportunity for terminals. As in the U.S., terminals appear to be largely available as "non-developmental items" (NDI) for commercial applications and specially developed under contract for military systems. Representative examples of transportable military terminals developed in Europe by Matra Marconi are shown Figure 4.5 and compare favorably with U.S. products. (Military examples are chosen because applications require high performance with serious weight limitation.)

A new area of interest is the PCS terminals that will be used in systems such as the Inmarsat Project 21 or the IRIDIUM system. It appears that industrial organizations in Europe will develop such items on speculation (i.e., as NDI). Airborne terminals for the Inmarsat systems are now coming into greater use, with over 200 terminals worldwide. Inmarsat actually provides "type certification" of these items offered by industry. The same is true for many types of Inmarsat terminals, not just airborne. Type certification will be of crucial importance in PCS because of the portability.

The HDTV and digital television concepts being explored in several EUTELSAT programs involve new waveform and compression coding. Technology already developed by Thomson CSF in image processing is applicable. Modulation and error correction coding for these applications are not considered research topics and require straightforward extension of existing products. There are only a few high speed modems (rate > 45 Mbits/sec) and only two products at 155 Mbits/sec (modems by ALCATEL and Thomson CSF).

MMIC and ASIC Technology

For selected applications, MMIC and ASIC devices are being developed. The design capability, computer aided design tools and limited experience have already been acquired. ALCATEL has developed ASICs for space use in silicon, CMOS and silicon on sapphire (SOS), for example. Marconi has a foundry likely to be type-qualified by ESA for supplying devices for satellites. GaAs solar cells are supplied by FIAR for use by Surrey Satellite Technology in its microsatellites.

A large number of Ka-band TVRO terminals have been developed and produced in Europe and employ MMIC low noise amplifier/down converter (LNA/DC) assemblies.

Summary

Europe's technology base is well adapted for meeting the challenge of producing smaller terminals. While manufacturing capacity was not examined, small terminals may not represent a great load in quantities of tens or hundreds of thousands. The U.S. probably has produced more VSATs at this time. The requirements of future systems may yet present technological challenges inviting very new technologies, but a slight extension of familiar technology may be adequate. New terminals may involve only a judicious combination of consumer product components, with specially developed MMIC and IC components, techniques and materials. The emphasis of the site presentations followed the established practice of centering on space and satellites with little attention being paid to technology advances or trends in earth terminals. With the need for ever-expanding quantities as such terminals become smaller, the manufacture of terminals may represent the largest industrial opportunity available in the next decade in satellite communications.


Figure 4.5. Representative Examples of Military Terminals Developed in Europe by Matra-Marconi (Portsmouth, U.K.)


Published: July 1993; WTEC Hyper-Librarian