DOI:10.1049/ree.1977.0020

出版商:IERE    

年代:1977

数据来源: IET

摘要:

Developments in experimental active and passive superdirective antennas are reviewed. Particular attention is given to the author's work on a two wavelength passive array consisting of nine open-ended waveguide radiators spaced one quarter-wavelength apart. The broadside superdirective patterns for this array are shown and the unnecessary restrictions on the bandwidth, due to the feeding system and the measuring site, are discussed. A new family of superdirective patterns is reported and it is shown that the far-field of a superdirective antenna starts at a distance which is no further from the antenna than that for the equivalent non-superdirective antenna. It is also shown that the high reactive field associated with superdirective arrays is confined to the immediate vicinity of the antenna.

DOI:10.1049/ree.1977.0021

出版商:IERE    

年代:1977

数据来源: IET

摘要:

Recent domain tip efforts, mainly the DOT memory of CMI and BASF and the MOD memory of TECSI and Crouzet have been directed toward lowering the cost per bit through an increase in the bit density on the substrate and more efficient manufacturing processes. Domain tip memory technology takes advantage of the low cost per bit of the basic magnetic film deposited on a glass substrate despite the lower density as compared to the cost of semiconductors or bubble memory processed substrates.The paper reports mainly on the recent design of MOD which allows unilateral propagation of domains with one level of conductors. Several prototypes in DOT as well as in MOD technologies have been constructed and operated, some of them of a capacity larger than 2 megabits, showing overall error rates better than 10−9without correction.

DOI:10.1049/ree.1977.0022

出版商:IERE    

年代:1977

数据来源: IET

摘要:

A system has been devised and tested successfully in a laboratory mock-up to tackle the problem of detecting the presence of a metal strip in the particularly hazardous environment of a steel works. This paper briefly outlines the environmental problems, and how they defeated more conventional techniques, before moving on to the basic principles involved with using microwave diffraction for detecting the strip. Modifications are then described to the fundamental concept which are needed to overcome practical problems.The paper finally outlines how the technique can be installed into the existing bed with very little disruption to the practical set-up and also gives a rough idea of costs involved.

DOI:10.1049/ree.1977.0023

出版商:IERE    

年代:1977

数据来源: IET

摘要:

In the current literature, the theoretical analyses which deal with the problem of additive coloured Gaussian noise (c.g.n.) assume that a pre-whitening filter is built into the receiver. This filter modifies the c.g.n. power spectrum density in such a way that, at the input of the threshold comparator, a bandlimited white Gaussian noise (w.g.n.) is obtained. The assumption of a pre-whitening filter is well justified for the purposes of theoretical analysis. Unfortunately, for practical systems, the design of a pre-whitening filter is not always feasible, as in the case of 1.544 Mbit/s data under voice (d.u.v.) hybrid microwave transmission.In this paper, the equations for the performance of a multilevel p.a.m. receiver (as is the case in d.u.v.) for a c.g.n. environment are presented and show that, without the insertion of the pre-whitening filter, the same results are obtained as in a w.g.n. environment. The validity of these results is demonstrated by using a number of noise filters to obtain c.g.n. for laboratory measurements and by practical field measurements on an eight-hop 6 GHz microwave system (RCA-MM-600) which employs 4-level p.a.m. transmission in a d.u.v. configuration.

DOI:10.1049/ree.1977.0024

出版商:IERE    

年代:1977

数据来源: IET

摘要:

Channel coding is universally employed in digital magnetic recording to match certain properties of the coded data to the characteristics of the recorder channel. In this paper, attention is focused primarily on the digital sum variation and d.c. content of various codes. The older, more familiar examples, such as NRZ, Manchester, enhanced-NRZ and Miller are compared with the more recently developed group, zero modulation and M2codes.

DOI:10.1049/ree.1977.0025

出版商:IERE    

年代:1977

数据来源: IET

摘要:

The different units making up a marine radar installation are first described, with particular emphasis on the display, where the greatest variety of design has recently appeared. System aspects are then discussed, especially the clutter problem, as well as reliability and maintenance.

DOI:10.1049/ree.1977.0026

出版商:IERE    

年代:1977

数据来源: IET