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KAMPALA INTERNATIONAL UNIVERSITY
DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING
TEL 4206: ELECTROMAGNETIC FIELDS
YEAR FOUR SEMSTER TWO, END OF SEMESTER EXAMINATION 2014/15
INSTRUCTIONS:
This Examination contains Five (5) questions.
Attempt any four (4) Questions for full mark.
The first four questions shall e marke! if more than five
questions are attempte!.
All Questions carry equal marks of "5#.
$e%in each Question on a fresh pa%e
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!"#$%&' O'" (25 M)*+#
) i) Explain -hat is meant y loa! resistance an! ra!iation
resistance of an antenna %ivin%
their si%nificance. (2 M)*+#ii)Account for the losses that occur
-ithin the antenna system an! state -ays of miti%atin%
such losses ( - M)*+#
. i) tate three circuit quantities an! three space quantities
that characteri/e an antenna ( -
M)*+#
ii) 0istin%uish et-een ack loe an! si!e loe (- M)*+#
iii) tatin% any vali! assumptions ma!e1 !erive the ra!iation
equation of an antenna an!
hence state three con!itions that are necessary to create
electroma%netic ra!iation ( 4
M)*+#
0istin%uish et-een 2mni !irectional1 isotropic an! !irectional
antenna statin% -here each
antenna fin!s !irect application ( 4 M)*+# 0efine the follo-in%
in relation to antenna ra!iation
% 3a!iation loe ( 2 M)*+#%% 3a!iation pattern ( 2 M)*+#
%%% po-er pattern ( 2 M)*+#
!"#$%&' T& (25 M)*+#
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a) ith reference to an antenna1 explain the follo-in% parameters
statin% the hypothesis -here
nee! e.
% nput mpe!ance ( 1 M)*+%% Effective area ( 2 M)*+#
%%% 3a!iate! po-er ( 2 M)*+#
%3 3a!iation ntensity ( 1 M)*+#) i) 0efine antenna efficiency
an! state three factors that affect the efficiency of an antenna.(
-
M)*+#
ii) 0istin%uish et-een the 6ain an! !irectivity of an antenna
an! %ive their mathematical
expressions explainin% all the parameters involve! (4 M)*+#
iii)hat is the fun!amental !ifference et-een the reactive near
fiel!1 ra!iatin% near fiel!
an! far fiel! re%ion of an antenna. ( - M)*+#
c) An antenna is characteri/e! y"' *V m
Er
= in far eld. At a point in far fiel!1
% Avera%e po-er !ensity1 ( )avW r
( - M)*+#%% 7ompute the total ra!iate! po-er ( - M)*+#
%%% Evaluate the maximum !irectivity of the antenna ( -
M)*+#
!"#$%&' T*"" (25 M)*+#
a) i) 0efine an Antenna Array ( 2 M)*+#
ii) 6ive three reasons for the use of antenna arrays over
in!ivi!ual elements (2 M)*+#
iii) Explain five !e%rees of free!om in the !esi%n of an antenna
array ( - M)*+#
. i) 8sin% illustrations1 !istin%uish et-een conformal1 planar1
circular an! linear Antenna
arrays ( 2 M)*+#
ii. 0efine stan!in% -aves an! account for their existence in
antenna systems an! explain ho-
they can e minimi/e! (- M)*+# i. Explain the si%nificance of
poynti% vector %ivin% its mathematical expression ( - M)*+#
ii. tate three properties satisfie! y the Electric an! 9a%netic
fiel!s in the far fiel! re%ion of
the antenna. (- M)*+#
i)Explain -hat you un!erstan! y the terms 3a!iation an! an
antenna clearly statin% their
ma:or role in -ireless telecommunication systems. ( 4 M)*+#
ii) 8sin% illustrations1 !istin%uish et-een roa!si!e an! En!
fire arrays ( - M)*+#
!"#$%&' F&!* ( 25 M)*+#
) ho- that for an ;
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sin"
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8se a neat !ia%ram to explain all the parameters use! (6 M)*+#.
From the expression aove of A.F1
% 0erive the requirements for achievin% the nulls of the A.F an!
hence state the necessary
an! sufficient con!itions for the existence for the nulls of the
array factor. ( - M)*+#
%% 0erive the locations of the maxima of the total ra!iate!
fiel! ( 4 M)*+#
iii 0efine eam nullin% an! eam steerin% ( 4 M)*+#
0efine the follo-in% parameters of an antenna
% $eam -i!th ( 2 M)*+#
%% +?$ ( 2 M)*+#
%%% F;$ ( 2 M)*+#
0istin%uish et-een 3a!ian an! stera!ian ( 2 M)*+#
!"#$%&' F%3" (25 M)*+#
a) i)0efine @3 an! 3 ( - M)*+#
ii) 0iscuss three causes of reflection alon% the
transmission
