CONFIDENTIAL BEE 4433

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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

CONFIDENTIAL BEE 4433

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(b) radiated power is 125.66 mW

[4 Marks]

[CO3, PO4]

QUESTION 3

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]

ZL Zo = 50Ω

l = 0.1 λ =

ZL = 5 + j25 Ω

CONFIDENTIAL BEE 4433

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[CO3, PO4]

END OF QUESTION PAPER

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 = l 2 .

(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 dB

Determine the maximum acceptable path loss.

[2 Marks]

[CO3, PO4]

END OF QUESTION PAPER