CS计算机代考程序代写 PAPER CODE NO.

PAPER CODE NO.
ELEC 411
EXAMINER: Prof Yi Huang
DEPARTMENT: EE&E Email: Yi.Huang@Liverpool.ac.uk
SECOND SEMESTER EXAMINATIONS REPLACEMENT 2019/20
Radio Propagation for Wireless Systems
INSTRUCTIONS TO CANDIDATES
The numbers in the right hand margin represent an approximate guide to the marks available for that question (or part of a question). Total marks available are 100.
Answer ALL Questions This is an Open-book Exam.
Additional Information:
Copying any material from another source, or colluding with any other person in the preparation and production of this work will be considered suspected academic misconduct and will be dealt with according to the University’s Academic Integrity Policy.
PAPER CODE ………………..ELEC411……………PAGE….1……..OF …………..6……………………..CONTINUED

1. a)
The polarisation is one of the most important features of electromagnetic
waves.
i)ˆˆ 6 Use E = xacos(t − z) + ybsin(t − z) as an example to explain
the concept of polarisation with the aid of a diagram. All the
polarisation types of a radiowave should be discussed.
ii) What is the polarisation used by mobile phones? Why? 6
The attenuation is another main feature of electromagnetic waves.
i) What are the main parameters determining the attenuation of 4
radiowave propagation in a medium?
ii) Justify why red light is normally used for danger signs. 4
iii) Compare the attenuation characteristics of a radiowave in free space 5
and a coaxial cable.
Total 25
b)
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2. The magnetic field of a radiowave is given as:
H = yˆ [ 1 0 e x p ( − 0 . 1 z + j ( 6   1 0 1 0 t − 2 0  z ) ) ]
a) Find a mathematical expression of the electric field of this wave. 4
b) Explain the meaning of this expression in terms of the field strength, 5
propagation direction, attenuation and polarisation.
c) Determine the wave frequency and speed, and then with the aid of a 6 diagram illustrate this wave as a function of distance z. Then comment
on if your results could be realised in reality.
d) Find the distance z where the power density is reduced to 10% of the 5 power density at z = 0.
e) If this wave is reflected by a perfect conductor at z = 0, obtain an 5 expression for the reflected magnetic field.
Total 25
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3.
A mobile radiowave operating at 2 GHz is reflected by a ground with a relative dielectric constant of 4 and conductivity of 0.
i) The incident angle is 45 degrees. Calculate the reflection coefficient for 10 the case when the wave has perpendicular polarisation and parallel polarisation, respectively. Then determine which polarisation normally
has a larger reflection coefficient;
ii) Find the incident angle and polarisation of the wave which will produce 8 a reflection coefficient of zero;
iii) Justify why the mobile radio frequency has been allocated at around 7 2 GHz while Sky Digital frequency has been allocated at around 12 GHz.
Total 25
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4.
A radio propagation channel is of interest to many wireless engineers. Path loss and delay spread are two of the most important parameters of such a channel.
i) Compare the free-space and two-wave path-loss models, and then suggest 8 a suitable path-loss prediction model for a concrete building (similar to
our Electrical Engineering building) and indicate the main parameters determining the path-loss.
ii) A typical impulse response of a radio channel is shown in the figure 8 below. The data rate of a mobile communication system (such as GSM)
is 270 kbps.
P (dB) 0 -10
-20 -30
0.5 1.0
1.5 2.0
t (s)
Calculate the mean excess delay, RMS delay spread and the maximum
excess delay (-10 dB) for this scenario.
iii) Estimate the coherent bandwidth of the channel in ii), and justify if this 4
channel is suitable for this mobile service without using an equaliser.
iv) Recently, the concept of “smart building” has become an interesting 5
research topic. From the radio propagation point of view, explain how you can make a building smart (such as to minimise or maximise the attenuation for some frequencies).
Total 25
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Reflectioncoefficient: Input impedance:
VSWR:
Intrinsic impedance: Snell’s law:
Equivalent impedance:
Loss tangent:
Skin depth:
Friis’ transmission formula:
Maxwell’s equations:
o=1.25710-6 H/m, 0 =8.85410-12F/m  =ZL−Z0
Important Constants and Equations
0
Zin (l) = Z0 ZL + jZ0 tan(l)
ZL + Z0
Z0 + jZL tan(l)
VSWR(l) = V max = V+ + V− = 1+ (l) V min V+ − V− 1− (l)
 = HE =  =120 r sin  
t = 1 = 1 1 sini 2 22
Z1= 1cosi;forparallelpol.
 / cos ; for perpendicular pol.
1i
Z2 = 2cost; forparallelpol.
 / cos ; for perpendicular pol. 2t
tan  =   =   
2 r t4r tr
 =1/ =
P = P (  )2G G
Radiation from a current Il:
Mean access delay and delay spread:
4
r 2r2 3r3
E =−jH H =J+ jE •E=/ •H=0
Er=2Il2cos( 1 − j )e−jr 4 2r2 3r3
E = Il  2 sin  ( j + 1 − j )e− jr
E = 0 
 Pt 
ii22 d =  t  p(t)dt = P  =  t p(t)dt − d
00
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