摘要:

Initially, the review takes a brief look at the various types of antenna systems that are used on satellites and shows that in terms of the measurement of their radiation characteristics, they can be categorised into two groups, i.e. low-gain (omnidirectional and quasi-omnidirectional) antennas, and medium- and high-gain antennas. With the first group, the main measurement difficulty lies with the suppression of multipath reflections, and the various range configurations that can be used to avoid or overcome this problem are described. Two of these are, for example, the ground reflection mode range and the use of baffles within an anechoic chamber. Following this, direct measurement ranges applicable to medium- and high-gain antennas are reviewed. These far-field approximation test range configurations include the elevated mode range, either in an outdoor environment or within an anechoic chamber, and the semi-open anechoic chamber. Subsequently, the review considers the various near-field and intermediate distance methods. Finally, some special techniques that have been devised to examine some particular satellite-antenna problems, such as the determination of the r.f. transparency of launch vehicle fairings and the effect of conductive thermal-control paint on satellite-reflector antennas, are presented. The review is principally from a European viewpoint.

DOI:10.1049/ip-a-1.1980.0063

出版商:IEE    

年代:1980

数据来源: IET

摘要:

The paper starts by reviewing the limitations of the existing methods of display of vector fields with particular reference to electromagnetic fields. A new method of display is then proposed which uses an arrow of fixed proportions to display the magnitude and direction of the vector field at each point at which it is known. The arrow head has thickness and the whole arrow is scaled in proportion to the strength of the field so that the orientation perpendicular to the plane of the paper is indicated by the body of the head and foreshortening of the image. The method is illustrated with some computer-generated diagrams. The computer program draws an arrow in the spacially correct position where the vector field is specified by three perpendicular components, having first scaled the arrow to the largest vector magnitude in the field. The system was devised particularly to display the results of finite element analysis of electromagnetic fields, but as an example, it is also used to display the electric and magnetic fields inside rectangular waveguide which have been calculated analytically. It will have applications in all branches of engineering and science where calculations give numerical values of field vectors.

DOI:10.1049/ip-a-1.1980.0064

出版商:IEE    

年代:1980

数据来源: IET

摘要:

A new instrument has been built for the measurement of hole diameter. It exploits a novel technique in which the diameter of a light beam oscillates, and it has shown a high performance for its cost. It lends itself to automated use.

DOI:10.1049/ip-a-1.1980.0065

出版商:IEE    

年代:1980

数据来源: IET

摘要:

Results are presented which support the predictions of a simple theory of sheath breakdown. The usual sheath equations are modified to allow for field-induced ionisation and secondary emission. The theory predicts that with increasing voltage the sheath expands to a certain point and then collapses catastrophically to a thickness determined by the external load. Measurements of the impedance of a plasma-filled gap reveal that a marked (∼ 102times) decrease in the magnitude of the impedance occurs as predicted by the theory.

DOI:10.1049/ip-a-1.1980.0066

出版商:IEE    

年代:1980

数据来源: IET

摘要:

The most common and maximum radii of craters on cathodes of copper, mild steel, silver, silver cadmium oxide and aluminium having various oxide film thicknesses, are reported following 4.5 A arcing of duration between 3.8 ns and 3.5 μs. The increase in crater radius with arc duration is examined in the light of a simple joule-heating model in a hemispherical region from which material is lost to form a crater. All the results except one conform with adiabatic joule heating, the one exception involving heat conduction into the cathode being no longer negligible. A brief comparison with cratering in cathodes of vacuum arcs is made, showing that these are of the latter type where joule heating provides the dominant energy input and the crater radius tends to increase to a value where this input is balanced by thermal conduction into the bulk metal. Close agreement with the model confirms earlier estimates by other methods of mean emitting site currents, current densities and lifetimes for copper and steel, and then enables these quantities to be estimated for the first time for silver, silver cadmium oxide, aluminium and also for mild steel with a relatively thick oxide film.

DOI:10.1049/ip-a-1.1980.0067

出版商:IEE    

年代:1980

数据来源: IET

摘要:

A description of several forms of laboratory study is given, and the major educational objectives likely to be attained via each mode analysed. Current practice of laboratory work in British undergraduate electrical engineering courses is then reviewed. The published methods of assessment of these study modes are considered, and the problems of value judgments of human qualities as well as intellectual skill development are highlighted. Particular attention is paid to the project method and the difficulties of this approach for both staff and students, particularly if this approach is to become an increasingly important component of study methods, are examined.

DOI:10.1049/ip-a-1.1980.0069

出版商:IEE    

年代:1980

数据来源: IET

摘要:

Aalborg University Centre (AUC) started in 1974 in Aalborg, North Jutland, as an experiment in engineering education. The history and the ideas behind the experiment are described in Section 1 of the paper. The key words in the educational method are problem (project)-orientation, teamwork and technology versus society and nature. The study is divided into two parts. The first year, the ‘base year’, is common to all students of engineering and natural sciences. The following years, the ‘superstructure’, have 5 different branches (‘sectors’) of engineering. The project-oriented, team (‘group’)-organised educational method works extremely well in the superstructure, which is described in detail in Section 3. The base year, which is described in Section 2, is a controversial year. It has several interesting features. Most of the initiative, for instance, is left over to the students, and there is a strong emphasis on technology-society-nature relations, training in teamwork and project-planning. But the outcome is arguable and a heated discussion as to the merits of the base year has been running for years inside (and outside) the university. The evaluation of the advantages and disadvantages of the AUC educational method is placed in connection with the descriptions in Sections 2 and 3, and is reasonably objective. In Section 4, the author puts forward a few personal, concluding remarks on the merits of the AUC and its methods.

DOI:10.1049/ip-a-1.1980.0070

出版商:IEE    

年代:1980

数据来源: IET

摘要:

The presence of minicomputers in electrical wholesale distribution inevitably affects the psychology of wholesaling and the attitude of management. In this paper, the problems of the Balmford Group are discussed, and the reason why we invested in a computer system. A brief review for the layman is given of the three types of computer available, and a description of the system eventually adopted, together with the software already in existence and that which had to be developed. This is followed by a description of how we changed our operating systems to use the equipment to the best advantage, of the subsequent effect on the work force, of advantages gained from the installation, and where future benefits may be found from realisation of the potentialities of our Multibus computer with its DBMS (Database Management Services) and BOPS (Balmford Order Processing System) programs.

DOI:10.1049/ip-a-1.1980.0071

出版商:IEE    

年代:1980

数据来源: IET

摘要:

The profits being earned by companies in the electrical sector in the United Kingdom today are insufficient to generate the new capital without which they cannot be competitive in international markets. This restricts growth and leads to falling employment, but choice of suitable development projects can minimise these effects.

DOI:10.1049/ip-a-1.1980.0072

出版商:IEE    

年代:1980

数据来源: IET

摘要:

The mechanism of industrial innovation can be described as a chain with feedback loops to bring out the iterative aspect which is essential to it. The level of the research and development effort in different industrial sectors is subject to prospects for further technological development. The low number of new high-technology companies founded in the 1970s in Europe and even in the USA is a matter of concern. The low mobility of qualified people, which is partly a result of national and linguistic fragmentation, impairs the position of European industries compared with companies in the USA. The European communities have not yet been able to formulate an industrial policy from which any industrial innovation policy might be derived. Public opinion is often fairly inconsistent in its attitude towards industrial innovation and this inevitably exposes industry to undue risks. The high level of prosperity attained by the Western nations is due in large measure to the pursuit of industrial innovation. Engineers and scientists, practised as they are in rational thinking, can make an important contribution to the synthesis that seems desirable between the technological culture of our civilisation and its social aspirations.

DOI:10.1049/ip-a-1.1980.0073

出版商:IEE    

年代:1980

数据来源: IET