Transition radiation of a relativistic electron bunch on a semi-infinite metal cylinder

Transition radiation of a relativistic electron bunch, which arises when it collides with the end face of a semi-infinite ideally conducting cylinder, is considered. An electron bunch moves along the axis of a semi-infinite cylinder. Expressions for the field strength of electromagnetic radiation in...

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Hauptverfasser: Balakirev, V.A., Onishchenko, I.N.
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Veröffentlicht: Національний науковий центр «Харківський фізико-технічний інститут» НАН України 2021
Schriftenreihe:Вопросы атомной науки и техники
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Zitieren:Transition radiation of a relativistic electron bunch on a semi-infinite metal cylinder / V.A. Balakirev, I.N. Onishchenko // Problems of Atomic Science and Technology. — 2021. — № 6. — С. 103-106. — Бібліогр.: 13 назв. — англ.

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spelling irk-123456789-1956472023-12-06T12:08:57Z Transition radiation of a relativistic electron bunch on a semi-infinite metal cylinder Balakirev, V.A. Onishchenko, I.N. Novel and non-standard acceleration technologies Transition radiation of a relativistic electron bunch, which arises when it collides with the end face of a semi-infinite ideally conducting cylinder, is considered. An electron bunch moves along the axis of a semi-infinite cylinder. Expressions for the field strength of electromagnetic radiation in the wave zone are obtained. The influence of the guiding properties of an ideally conducting cylinder on the directional diagram of the transition radiation is investigated. Розглянуто перехідне випромінювання релятивістського електронного згустка, що виникає при його зіткненні з торцем напівнескінченного ідеально провідного циліндра. Електронний згусток рухається вздовж осі циліндра. Отримано вирази для напруженості поля електромагнітного випромінювання в хвильовій зоні. Досліджено вплив направляючих властивостей ідеально провідного циліндра на діаграму направленості перехідного випромінювання. Рассмотрено переходное излучение релятивистского электронного сгустка, возникающее при его столкновении с торцом полубесконечного идеально проводящего цилиндра. Электронный сгусток движется вдоль оси полубесконечного цилиндра. Получены выражения для напряженности поля электромагнитного излучения в волновой зоне. Исследовано влияние направляющих свойств идеально проводящего цилиндра на диаграмму направленности переходного излучения. 2021 Article Transition radiation of a relativistic electron bunch on a semi-infinite metal cylinder / V.A. Balakirev, I.N. Onishchenko // Problems of Atomic Science and Technology. — 2021. — № 6. — С. 103-106. — Бібліогр.: 13 назв. — англ. 1562-6016 PACS: 41.75.Lx, 41.85.Ja, 41.69.Bq DOI: https://doi.org/10.46813/2021-136-103 http://dspace.nbuv.gov.ua/handle/123456789/195647 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України
institution Digital Library of Periodicals of National Academy of Sciences of Ukraine
collection DSpace DC
language English
topic Novel and non-standard acceleration technologies
Novel and non-standard acceleration technologies
spellingShingle Novel and non-standard acceleration technologies
Novel and non-standard acceleration technologies
Balakirev, V.A.
Onishchenko, I.N.
Transition radiation of a relativistic electron bunch on a semi-infinite metal cylinder
Вопросы атомной науки и техники
description Transition radiation of a relativistic electron bunch, which arises when it collides with the end face of a semi-infinite ideally conducting cylinder, is considered. An electron bunch moves along the axis of a semi-infinite cylinder. Expressions for the field strength of electromagnetic radiation in the wave zone are obtained. The influence of the guiding properties of an ideally conducting cylinder on the directional diagram of the transition radiation is investigated.
format Article
author Balakirev, V.A.
Onishchenko, I.N.
author_facet Balakirev, V.A.
Onishchenko, I.N.
author_sort Balakirev, V.A.
title Transition radiation of a relativistic electron bunch on a semi-infinite metal cylinder
title_short Transition radiation of a relativistic electron bunch on a semi-infinite metal cylinder
title_full Transition radiation of a relativistic electron bunch on a semi-infinite metal cylinder
title_fullStr Transition radiation of a relativistic electron bunch on a semi-infinite metal cylinder
title_full_unstemmed Transition radiation of a relativistic electron bunch on a semi-infinite metal cylinder
title_sort transition radiation of a relativistic electron bunch on a semi-infinite metal cylinder
publisher Національний науковий центр «Харківський фізико-технічний інститут» НАН України
publishDate 2021
topic_facet Novel and non-standard acceleration technologies
url http://dspace.nbuv.gov.ua/handle/123456789/195647
citation_txt Transition radiation of a relativistic electron bunch on a semi-infinite metal cylinder / V.A. Balakirev, I.N. Onishchenko // Problems of Atomic Science and Technology. — 2021. — № 6. — С. 103-106. — Бібліогр.: 13 назв. — англ.
series Вопросы атомной науки и техники
work_keys_str_mv AT balakirevva transitionradiationofarelativisticelectronbunchonasemiinfinitemetalcylinder
AT onishchenkoin transitionradiationofarelativisticelectronbunchonasemiinfinitemetalcylinder
first_indexed 2025-07-16T23:45:14Z
last_indexed 2025-07-16T23:45:14Z
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fulltext ISSN 1562-6016. ВАНТ. 2021. № 6(136) 103 https://doi.org/10.46813/2021-136-103 TRANSITION RADIATION OF A RELATIVISTIC ELECTRON BUNCH ON A SEMI-INFINITE METAL CYLINDER V.A. Balakirev, I.N. Onishchenko National Science Center “Kharkov Institute of Physics and Technology”, Kharkiv, Ukraine E-mail: onish@kipt.kharkov.ua Transition radiation of a relativistic electron bunch, which arises when it collides with the end face of a semi- infinite ideally conducting cylinder, is considered. An electron bunch moves along the axis of a semi-infinite cylin- der. Expressions for the field strength of electromagnetic radiation in the wave zone are obtained. The influence of the guiding properties of an ideally conducting cylinder on the directional diagram of the transition radiation is in- vestigated. PACS: 41.75.Lx, 41.85.Ja, 41.69.Bq INTRODUCTION The effects of transition and diffraction radiation of relativistic electron bunches [1 - 4] can underlie the pro- cesses of excitation of pulsed electromagnetic radiation in a wide frequency range [5 - 10]. In [10] the process of excitation of an infinite ideally conducting cylinder by a relativistic electron bunch was investigated. There- at the situation was considered when an electron bunch collides with a cylinder perpendicular to its cylindrical surface. Below we will consider a semi-infinite ideally conducting cylinder, which is excited by a relativistic electron bunch when it collides with the end face of the cylinder. It is in this way the ultra-wideband antennas were excited by a relativistic electron beam [7 - 9]. Ex- pressions for the intensity of electromagnetic radiation in the wave zone are obtained. The directional diagram of transition radiation and, first of all, the influence of the guiding properties of a cylindrical conductor on its formation is investigated. 1. STATEMENT OF THE PROBLEM. BASIC EQUATIONS We consider a semi-infinite ideally conducting circu- lar cylinder of radius a. A relativistic electron bunch moves in vacuum along the cylinder axis and collides with its face end. For simplicity, we will consider an infi- nitely thin tubular electron bunch with a current density 0 0( ) /1 2 z b b r r t z v j e Q T r t t            , (1) where ze is the unit vector in the longitudinal direction, Q is the charge of the bunch, 0r is the radius of the bunch, 0r a , 0v , bt are velocity and duration of the bunch, 0( )r r  is the delta function. The dimensionless function ( )T  describes the longitudinal density profile of the bunch and satisfies the normalization condition ( ) 1T d     , where ( ) ( )T T   is symmetrical function. Let us represent the excited electromagnetic field and the current density in the form of Fourier integrals over frequencies. So, for example, for a magnetic field we have ( , , ) ( , ) ,i tH r z t H r z e d        (2) where 1 ( , ) ( , , ) 2 i tH r z H r z t e dt       is Fourier amplitude of the magnetic field. The system of Maxwell's equations for the compo- nents of the Fourier amplitudes of the electromagnetic field has the form 0 r zE E ik H z r          , (3a) 0 0 ( )1 2 lik z z b r rQ r H ik E T e r r r ct r            , (3b) 0 r H ik E z       , (3c) where 0 /k c , 0/lk v , 00 0 1 2 i t b t T T e dt t              . Let's divide the space into three regions: 0 0, 0;I r r z    0 , 0;II a r r z    , .III r a z       The problem is reduced to solving the inhomogene- ous system of Maxwell's equations (3) with the follow- ing boundary conditions. On the current surface 0r r , the longitudinal component of the electric field is con- tinuous, and the magnetic field experiences a leap 0r r , ( 0) ( 0)II I z zE z E z    , 0 2 ( 0) ( 0) lik zII I b Q H z H z T e ct r        . (4) On the boundary r a in the left half-space 0z  , the tangential components of the electromagnetic field are continuous r a , ( 0) ( 0)III II z zE z E z    , ( 0) ( 0)III IIH z H z    . (5) In the right half-space 0z  on the surface of a per- fectly conductive cylinder, the longitudinal component of the electric field vanishes r a , ( 0) 0III zE z   . (6) And, finally, at the end of a semi-infinite cylinder, the radial component of the electric field also vanishes 0a r  , ( 0, ) ( 0, ) 0I II r rE z r E z r     . (7) ISSN 1562-6016. ВАНТ. 2021. № 6(136) 104 2. METHOD OF SOLUTION. MAIN RESULTS In the system under consideration, the electromag- netic field disappears at infinity, so the electromagnetic field can be sought in the form of a superposition of waves propagating in the longitudinal direction 1 0( , ) ( ) ( )I ikz zE r z e k J vr e dk     , (8a) 1 0 1 1( , ) ( ) ( )I ikzH r z ik e k v J vr e dk       , (8b) (1) 2 0 3 0( , ) ( ) ( ) ( ) ( )II ikz zE r z e k J vr e k H vr e dk       , (8c) 1 (1) 0 2 1 3 1( , ) ( ) ( )II ikzH r z ik v e J vr e H vr e dk         ,(8d) (1) 4 0( , ) ( ) ( )III ikz zE r z e k H vr e dk     , (8e) 1 (1) 0 4 1( , ) ( ) ( )III ikzH r z ik e k v H vr e dk       , (8f) 2 2 0v k k  , 1 4 ( )... ( )e k e k are the sought amplitudes of the fields in the corresponding regions, (1)( ), ( )n nJ vr H vr are the Bessel and Hankel functions, 0.1n  . Substituting fields (8) into boundary conditions (4) - (6), we obtain a system of paired integral equations, which, using the Wiener-Paley-Rappoport lemma, can be reduced to the following system of functional equa- tions (1) 1 2 0 0 3 0 0[ ( ) ( )] ( ) ( ) ( ) ( )e k e k J vr e k H vr k   , (9a) (1)0 1 2 1 0 3 1 0{[ ( ) ( )] ( ) ( ) ( )} ( ) k i e k e k J vr e k H vr k v       0 2 1 2 ( )b l Q T ct r i k k     , (9b) (1) 2 0 3 4 0 0( ) ( ) [ ( ) ( )] ( ) ( )e k J va e k e k H vr k    , (9c) (1)0 2 1 3 4 1 0{ ( ) ( ) [ ( ) ( )] ( )} ( ) k i e k J va e k e k H vr k v     , (1) 4 0 0( ) ( ) ( )e k H vr k  , (9d) where ( )k , ( )k  , ( )k  , ( )k are analytic func- tions in the lower half-plane of the complex variable k, and ( )k  is the analitic function in the upper one, Im 0.lk  From the boundary condition at the face end of the cylinder (7) it follows that the following amplitudes are even ( ) ( ), 1,2,3e k e k     . (10) It can be shown that the system of functional equa- tions (9), taking into account relations (10), is equiva- lent to the system of Hilbert boundary value problems on the real axis Im 0k  ( ) ( ) 0,k k    (11a) 2 2 0 2 ( ) ( ) , ( )b l Q k k k T ct r i k k         (11b) ( ) ( ) ( ) ( )k k k k         , (12a) ( ) ( ) ( )[ ( ) ( )]k k H k k k          , (12b) 0 1 0 0 0( )[ ( ) ( )] ( )[ ( ) ( )] k i J vr k k J vr k k v           0 1 0 0 ( )[ ( ) ( )] ( )[ ( ) ( )] ka i J va k k J va k k r v                0 0 02 (1) 2 2 00 0 2 ( ) ( ) 2 ( ) ( ) ( ) l b l k kk k Q T J vr ct rv r H va i k k           , where ( ) ( ), ( ) ( )k k k k          etc, (1) 0 1 (1) 0 ( ) ( ) ( ) ik H va H k v H va  . Solutions of the boundary problems (11a), (11b) are found trivially ( ) ( ) 0k k    , 0 2 1 ( ) 2 ( )b l Q k T ct r i k k       , 0 2 1 ( ) 2 ( )b l Q k T ct r i k k       . Using the Sokhotsky formulas [11], the system of boundary problems (12) can reduce to the following singular equation for the function      ˆ ˆ ˆ2 ( ) ( ) ( ) ( ) ( ) ( )I k L k LH k k H k L k     0 0 2 2 0 ( )4 ( ) ( ) l b l J vr kQ T ct a J va i k k     , (13) where 0 1 0 ( ) ( ) ( ) ik J va I k v J va  , 1 ( )ˆ ( ) . f k Lf k dk i k k       (14) Integral (14) should be understood in the sense of the principal value. It is not possible to find a general solution to this integral equation. However, in the limit- ing case of a conducting cylinder of small radius 0 1k a  , the solution can be found approximately. In this limiting case, the term in the integral equation (13), which proportional 0( ) ~I k k a can be neglected. Then the integral equation is simplified and takes the form 2 2 4ˆ ˆ( ) ( ) ( ) ( ) . ( ) l b l kQ LH k k H k L k T ct a i k k        (15) After replacement ( ) ( ) ( )U k H k k the simplified integral equation (15), in turn, is reduced to the boundary value problem [12] 2 2 2 ( ) l b l kQ U H T ct a i k k         , the solution of which can be found explicitly 0 2 0 ( )4 ( ) (2 ) l b X k k kkQ k T ct a k i         0 2 2( )( )( )lC k k dk X k k k k k       , (16) where ( )X k is solution of homogeneous conjugation problem ( ) ( ) ( )X k G k X k  , (1) 0 (1) 1 ( ) ( ) ( ) H va G k iH va  . The solution to this boundary value problem has the form [11] 1 ln ( ) ( ) exp 2 C G k X k dk i k k      , 1 ( ) ( ) X k X k     . (17) ISSN 1562-6016. ВАНТ. 2021. № 6(136) 105 The contour C runs along the real axis and bypasses the singularity k k  from below. The integral included in (16) is easily calculated by closing the integration contour into the lower half-plane. As a result, we obtain 0 0 0 ( )(2 ( ) ( ) 2 ( ) ( ) l b l l k k k kQ X k k T сt ak i k k X k          . Relation (9d), taking into account the obtained ex- pression for the function ( )k  , makes it possible to de- termine the amplitude 4 ( )e k for the region r a and, accordingly, the expression for the magnetic field in this region 02 2 ( ) lIII b l k kQT H ct a X k         (1) 1 (1) 00 ( ) ( ) ( )( ) ikz l X k H vr e dk H vak k k k        . (18) We are primarily interested in electromagnetic radia- tion in the wave zone 0 1k R  , R is the distance from the origin of coordinates to the point of observation. Using the asymptotic representation of the Hankel func- tion for large values of the argument 1vr  , after passing to a spherical coordinate system cos , sinz R r R   ( is polar angle) and replac- ing the integration variable 0 cosk k w instead of the integral representation (18), we obtain 0 0 /4 0 ( )2 2 sin2 ( ) lIII i b l k k kQ H i T e ct a k RX k           0 cos( )0 (1) 0 0 ( cos ) sin 1 cos( sin ) i ik R w i X k w w e dw wH k w          . (19) The integration contour runs along a straight line from i   to  , then along a segment 0w   and again along a straight line from 0 to i . In the wave zone, integral (19) can be estimated by the saddle-point method. The saddle point w  lies within the real axis line segment. As a result, we obtain the following ex- pression for the radiation field 0 0 0 ( ) sin (1 cos ) 1 cos lIII b l k k kQ H T ct k             0 0( cos ) ( ) ik R l X k e RX k    , (20) 0 0 /v c  . The function ( )X k can be calculated ex- actly. However, in the considered quasistatic approxi- mation 0 1k a  , we can use the asymptotic representa- tion of this function [13] 0 0 0 0 ln 1 ( ) 2( ) ln 2 ( ) i i k a X k ik k a a k k k       , 1.78  is Euler's constant. Accordingly, the expres- sion for the magnetic field of radiation (20) takes the form 0 1 cos ln sin 2 III b Q H T ict k a          0 0 sin sin 1 cos 1 cos ik R e R              , (21) where 0 00 0 0 22 ln ln (1 ) k ak a         , 0 is a relativistic factor. The first term in formula (21) describes the transition radiation arising from the colli- sion of an electron bunch with the end face of a semi- infinite conducting cylinder. The second term has a sin- gularity for the angle 0  . The radiation field along the cylindrical conductor goes to infinity. This effect is explained by the guiding properties of a perfectly con- ducting cylinder [13]. The feature of the field is integrable. The total energy flow remains finite. An analysis of the radiation pattern shows that the maxi- mum of the radiation field in the direction characteristic of transition radiation 01/  is never formed. This is due to the strong distortion of the radiation field in this direction by radiation focused along the surface of the cylindrical conductor. Turning to infinity towards 0  , the amplitude of the radiation field decreases monotonically with increasing polar angle  . Thus, a thin semi-infinite cylinder is actually an antenna of a traveling wave excited by a relativistic electron bunch. Directly from the form of the second term in square brackets in formula (21) it follows that the antenna radia- tion excites a current induced on the surface of a perfectly conducting cylinder, which propagates along the cylinder at the speed of light. Moreover, this current is in antiphase with respect to the current of the electron bunch. A single bunch excites an electromagnetic field with a continuous frequency spectrum, and the shape of the radiation pulse is determined by the Fourier integral (2), which is conveniently represented in the form  * 0 III III i t III i tH H e H e d         . (22) Taking into account the expression (21), relation (22) takes the form 2 2 20 0 cos sin ( ) 2 4 III b L t t Q F H T d Rct L                   ,(23) where 0 sin ( ) (1 cos )(1 cos ) F         , 0ln     , 0 0 1 ln 2sin 2 L                , 0 0 2 c a     , R t t c   . For small polar angles 1  under the condition 0 0 0 0 ln ~ ln 4 btL          expression (23) is essentially simplified and takes the form   2 0 ( ) /III b Q F H t R c Rct       . (24) Function ISSN 1562-6016. ВАНТ. 2021. № 6(136) 106     0 00 0 ln / cos / ln t R c T t R c d             describes the shape of the transition radiation pulse. For not too small angles 0 0 0 1 ln ~ ln lnbt       or 0 0 1 bt     we have   / / b t R c t R c T t          , that is, the electromagnetic pulse exactly repeats the shape of the electron bunch. Otherwise, the shape of the electromagnetic pulse will depend, albeit weakly, on the polar angle  and will slightly differ from the shape of the electron bunch. CONCLUSIONS Transition radiation of a relativistic electron bunch, which arises when it collides with the end face of a semi-infinite perfectly conductive cylinder, is consid- ered. The electron bunch moves along the cylinder axis. Expressions for the intensity of the magnetic field of radiation in the wave zone are obtained. It is shown that this expression contains two terms. The first term de- scribes the actual transition electromagnetic radiation of the electron bunch. Its characteristics substantially de- pend on the energy (relativistic factor) of the electron bunch. The second term describes the radiation of the current induced on the surface of a perfectly conducting cylinder and propagating along the cylinder at the speed of light in vacuum. The strength of this field has integrable singularity (turns to infinity) strictly along the surface of the cylinder. The peculiarity is due to the guiding properties of a perfectly conducting cylinder. The spatial structure (directional pattern) of this elec- tromagnetic radiation does not depend on the energy of the bunch and is determined by the geometry of the cy- lindrical antenna under consideration. The amplitude of the radiation field decreases monotonically with increas- ing polar angle  . The maximum of the radiation field in the direction characteristic of transition radiation 01/  is never formed. This is due to the strong dis- tortion of the radiation field in this direction by radia- tion propagating along the surface of the cylindrical conductor. 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Singular integral equations. M.: “Science”, 1968, 512 p. 13. L.A. Weinstein. Theory of diffraction and method of factorization. M.: “Soviet radio”, 1966, 431 p. Article received 12.10.2021 ПЕРЕХОДНОЕ ИЗЛУЧЕНИЕ РЕЛЯТИВИСТСКОГО ЭЛЕКТРОННОГО СГУСТКА НА ПОЛУБЕСКОНЕЧНОМ МЕТАЛЛИЧЕСКОМ ЦИЛИНДРЕ В.А. Балакирев, И.Н. Онищенко Рассмотрено переходное излучение релятивистского электронного сгустка, возникающее при его столкновении с торцом полубесконечного идеально проводящего цилиндра. Электронный сгусток движется вдоль оси полубесконечно- го цилиндра. Получены выражения для напряженности поля электромагнитного излучения в волновой зоне. Исследова- но влияние направляющих свойств идеально проводящего цилиндра на диаграмму направленности переходного излуче- ния. ПЕРЕХІДНЕ ВИПРОМІНЮВАННЯ РЕЛЯТИВІСТСЬКОГО ЕЛЕКТРОННОГО ЗГУСТКА НА НАПIВНЕСКIНЧЕННОМУ МЕТАЛЕВОМУ ЦИЛІНДРІ В.А. Балакiрев, I.М. Онiщенко Розглянуто перехідне випромінювання релятивістського електронного згустка, що виникає при його зіткненні з тор- цем напівнескінченного ідеально провідного циліндра. Електронний згусток рухається вздовж осі циліндра. Отримано вирази для напруженості поля електромагнітного випромінювання в хвильовій зоні. Досліджено вплив направляючих властивостей ідеально провідного циліндра на діаграму направленості перехідного випромінювання.