摘要:

The emergence of satellite land mobile services over the last 10 to 15 years is described together with future trends. The difficulties of providing a commercially viable voice service are discussed and alternatives, such as inclined orbit systems and satellites with very large antennas, are suggested as ways in which the initial disadvantages might be overcome. Data services for satellite land mobile traffic and the possibilities of including radio determination of vehicle location as part of these data services are also considered. Future systems, which could have their architecture strongly influenced by the use of onboard processing, are discussed.

DOI:10.1049/ecej:19890051

出版商:IEE    

年代:1989

数据来源: IET

摘要:

A study of current dominant coupling in a system comprising a large number of mutually coupled braided coaxial transmission lines is presented. An efficient model for the crosstalk is developed in the frequency domain using distributed circuit parameters and the concept of transfer impedance. The lines are assumed to be lossy and to have frequency-dependent per-unit-length parameters, and further losses due to the braided nature of the outer conductors are accounted for in the analysis. The validity of the coupling model is tested against measurements in the frequency domain before using fast Fourier transforms to evaluate the time domain responses.

DOI:10.1049/ecej:19890052

出版商:IEE    

年代:1989

数据来源: IET

摘要:

The concept of EFTPOS is introduced and its development from cash dispensers and credit cards, through smartcards to the concept of a single, universal multifunction card is outlined. Such a card could subsume the array of cards that many individuals now possess, as well as contain advanced features. The article includes an examination of the main technologies used with a strong emphasis on the security measures employed, since fraud is a major concern.

DOI:10.1049/ecej:19890057

出版商:IEE    

年代:1989

数据来源: IET

摘要:

Radars and their associated antennas evolved more or less independently for a number of years, but a gradual marriage began in the 1960s with the advent of improved and relatively cheap signal-processing techniques. Today's advanced radars with electronically steered beams, incorporating T/R modules and signal-processing equipment at the array elements, appear to be the realisation of the early pioneers' pipe dreams. Part 1 of this paper provides a brief review of developments to date and examines some of the trade-offs required in the design of radar systems for various functions. Part 2* concentrates on antenna characteristics affecting radar design and provides some pointers to future trends.

DOI:10.1049/ecej:19890058

出版商:IEE    

年代:1989

数据来源: IET

摘要:

The dramatic reductions in the cost, size, weight and power consumption of electronic equipment during the last decade have had an especially profound effect on the practice of radionavigation. Traditional users of radio aids now have equipment of smaller size and increased reliability and performance which provide many additional functions by virtue of their greatly enhanced computing power. At the same time a completely new consumer market has been created which has come to dominate the entire radionavigation industry. This process of change is illustrated by examining the development of low-cost receivers for three radionavigation systems: direction-finding, Loran-C and Decca Navigator. The paper then shows how the use of other marine and aeronautical navigation aids has changed and describes novel applications of radio techniques made possible by these technical developments.

DOI:10.1049/ecej:19890059

出版商:IEE    

年代:1989

数据来源: IET