CONFIDENTIAL
BEE 4433
PART B
QUESTION 1
A 1-m long dipole antenna is driven by a 150 MHz source having a source resistance
of 50 ohms and a voltage of 100 V. If the ohmic resistance of the antennas is given by
RL = 0.625 ohms, find the:
(a) Current going into the antenna (Iant)
(b) Power dissipated by the antenna
(c) Power radiated by the antenna
[6 Marks]
[CO3, PO4]
QUESTION 2
The maximum radiation intensity of a 90% efficiency antenna is 200 mW/unit
solid angle. Find the directivity and gain (dimensionless and in dB) when the
(a) input power is 125.66 mW
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CONFIDENTIAL
BEE 4433
(b) radiated power is 125.66 mW
[4 Marks]
[CO3, PO4]
QUESTION 3
l = 0.1 λ =
ZL
Zo = 50Ω
ZL = 5 + j25 Ω
The 0.1 λ length line shown has a characteristic impedance of 50 Ω and is
terminated with a load impedance of ZL =5+ j25
a. Locate zL on the Smith chart.
b. What is the impedance at l = 0.1 λ?
c. Find the reflection coefficient of the load (ГL).
[5 Marks]
6
CONFIDENTIAL
BEE 4433
[CO3, PO4]
END OF QUESTION PAPER
7
PART B
QUESTION 1
A three-element array of isotropic sources has the phase and magnitude relationships shown in the
figure below. The spacing between the elements is
d=l2.
(a) Find the array factor.
[2 Marks]
[CO3, PO4]
QUESTION 2
Given is a E-plane sectoral horn with the dimensions ρ1 = 20l and a = 0.5l .
(a) Find its optimum aperture dimensions for maximum normalized directivity.
Compute the total flare angle of the horn.
[6 Marks]
[CO3, PO4]
QUESTION 3
A mobile phone is located 5 km away from a base station. It uses a vertical l / 4 monopole antenna
with a gain of 2.55 dB to receive cellular radio signals. The free space E-field at 1 km from the
transmitter is measured to be 10-3 V/m. The carrier frequency used for this system is f = 900MHz.
(a) Find the length and effective aperture of the receiving antenna.
[3 Marks]
[CO3, PO4]
QUESTION 4
A base station transmits a power of 10 W into a feeder cable with a loss of 10 dB. The transmit
antenna has a gain of 12 dBd (dBd refers to a l /2 dipole) in the direction of a mobile receiver, with
antenna gain 0 dBd and feeder loss 2 dB. The mobile receiver has a sensitivity of –104 dBm.
Quantity
Value inoriginal units
Value inconsistent units
PT : transmitted power
10 W
10 dBW
GT : gain of transmitting antenna
12 dBd
14.15 dBi
GR : gain of receiving antenna
0 dBd
2.15 dBi
PR : received power
–104 dBm
–134 dBW
LT : transmitter feeder loss
10 dB
10 dB
LR : receiver feeder loss
2 dB
Determine the maximum acceptable path loss.
[2 Marks]
[CO3, PO4]
END OF QUESTION PAPER
dB