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      SCIENCES

       Waves, Field Directors – Pierre-Noël Favennec, Frédérique de Fornel

      Electromagnetism, Subject Head – Pierre-Noël Favennec

      Electromagnetic Waves 2

       Antennas

       Coordinated by

      Pierre-Noël Favennec

      First published 2020 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.

      Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:

      ISTE Ltd

      27-37 St George’s Road

      London SW19 4EU

      UK

       www.iste.co.uk

      John Wiley & Sons, Inc.

      111 River Street

      Hoboken, NJ 07030

      USA

       www.wiley.com

      © ISTE Ltd 2020

      The rights of Pierre-Noël Favennec to be identified as the author of this work have been asserted by him in accordance with the Copyright, Designs and Patents Act 1988.

      Library of Congress Control Number: 2020937434

      British Library Cataloguing-in-Publication Data

      A CIP record for this book is available from the British Library

      ISBN 978-1-78945-007-1

      ERC code:

      PE2 Fundamental Constituents of Matter

       PE2_6 Electromagnetism

       Pierre-Noël FAVENNEC

       ArmorScience, Lannion, France

      Any electric charge set in motion produces electromagnetic radiation which propagates in space. This property is the basis of radioelectric, or photonic radiation production, used in particular in radio, television and communication systems among others. Any system supplied with electricity, or any element provided with electric charge, emits electromagnetic radiation and generates an electric and/or magnetic field in its close, or even distant, vicinity which is known as an “electromagnetic field”.

      Before Maxwell’s work, we understood physical reality in terms of material points. After it, we represented physical reality with continuous fields. The concept of a field finds its origin, and its name, in the idea of describing a physical phenomenon from an underlying medium, which would explain the physical properties of space (a field of forces for a field of wheat subjected to the wind). Following Maxwell’s research, the fields acquired an autonomous existence and reached the status of physical beings in their own right, no longer describing “the place where” but “the thing that”. This movement was largely supported by the development of the mathematical formalism of the fields, in terms of partial differential equations. This, with regard to electricity and magnetism, is the content of Maxwell’s theory which he published in 1861.

      The electromagnetic field is the set of vector fields (

,
and the magnetic field
and
.

      Electromagnetic waves are produced by excited matter. The deexcitation of the excited source produces around it a periodic variation of the electromagnetic field which propagates gradually in the vacuum at the phase speed (or propagation speed) close to 300,000 km per second. Depending on their emission frequency domain, they have different names: radio waves for the lowest frequencies, infrared waves, visible optical waves, then ultraviolet, then for the highest frequencies, X-rays and gamma rays. The electromagnetic wave propagates: a variable electric field generates a variable magnetic field and conversely a variable magnetic field generates a variable electric field. The conjoint propagation of these variations in a region constitutes a continuous wave phenomenon, capable of propagating (across the vacuum at 300,000 kilometers per second), transporting energy without the need for material support.

      Waves are vibrations that propagate from one place to another in space, in a material medium or in a vacuum. Electromagnetic vibrations (electromagnetic waves) are waves obeying the laws of electromagnetism. Mechanical vibrations (pendulum, acoustics,

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