ELEC0019-A5U 2021
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ELEC0019-A5U 2021
SECTION 1
Answer ALL questions in this section
Note that the questions have different weights
For the following electric field vectors propagating in air, find the corresponding phasors for the electric and magnetic fields and give the unit vector in the direction of propagation.:
(a) E(一) = (2
3
+ 
)100 cos(Ot 
3x + 2y + 0)
(b) E(一) = (
+ 
+ 
) 28cos(Ot 
x + 2y 
z + 
4)
The electric field of a plane wave passing normally from a material with a dielectric constant (or relative permittivity) c1r = 4 , permeability 
= 
0 and conductivity G = 0 to a material with c2r = 9; 
= 4
0 ; G = 0 is given by:E(一) = 
100 cos(Ot 
6
x) (in mV m 
1 ).
(a) Write the complete time domain expressions for the incident, reflected and transmitted electric and magnetic fields.
[10 marks] (b) Find the time average power transmitted through a surface of 2m2 area and oriented
such that its normal forms an angle of 17° with the z-axis.
[4 marks]
(c) What is the frequency of this wave?
[2 marks]
A glass isosceles prism, as the one shown in Fig. 3. 1, is used in many optical instruments. If the relative permittivity of the glass is cr = 4 .
(a) What is the critical angle for the reflections inside the prism?
(b) What is the percentage of light power reflected by the prism?
Fig. 3.1
A right-handed circularly polarized wave represented by the phasor
E(一)(z) = E0 (
一 j
)e一jk0z
is normally incident on a flat perfectly conducting wall at z = 0..
(a) Determine the polarization type of the reflected wave.
(b) Find the total instantaneous electric field.
(c) Find the total instantaneous magnetic field.
(d) Obtain the induced surface current in the wall.
A rectangular waveguide is operated at 30 GHz. If the cutoff frequency of the TM21 mode is 18 GHz, find:
(a) The phase constant [2 marks]
(b) The wavelength [1 mark]
(c) The phase velocity [1 mark]
(d) The wave impedance of this mode [1 mark] (e) If it is operated now at 15 GHz, find the distance over which the fields of this mode will reduce by 20 dB (a factor of 10) [5 marks]
2022-08-16