# Module: Antenna And Radio Wave Propagation

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BEng.(Hons) Electronic Engineering
Cohort: BEE/10B/FT
Special Resit Examinations for September 2014
MODULE: ANTENNA AND RADIO WAVE PROPAGATION
MODULE CODE: TELC 2104 Duration: 2 Hours 15 mins
Instructions to Candidates:
question number clearly. 4. Always start a new question on a fresh page. 5. Questions do not carry equal marks. 6. Total marks: 100.
This question paper contains 3 questions and 4 pages.

Antenna and Radio Wave Propagation (TELC2104)

Page 1 of 4
SITE/September Resit

QUESTION 1 :(40 Marks)

(a)

(i) Explain what is meant by “An antenna with high radiation

intensity”.

(ii) One of the resistive parts of antenna is the loss resistance.

What is the impact of having a high loss resistance?

(3 Marks) (2 Marks)

(b) Prove that when an antenna is connected to a communication system at the best condition, the load resistance equals the source resistance. (5 Marks)

(c) Determine (1) the amplitude and direction of the principal maximum, (2) the amplitude ratio of the largest secondary maximum (sidelobe) to the principal maximum and, (3) the width of the principal lobe for each of the following linear antenna arrays:

(i) 4 elements 0.4 λ apart and fed with equal amplitude and in-

phase currents;

(6 Marks)

(ii) 12 elements λ/4 apart and fed with currents of equal

magnitude but with a progressive phase shift of -90 (8 Marks)

between elements.

(d) Consider the array pattern (as normalized electric field, ET / E0 versus , where is measured from the line of the array, that is, 90 for broadside) for an array of 2 elements (considered non-directional radiators) spaced λ/2 apart fed with currents of equal amplitude and phase.

(i) Determine, by the method of multiplication of patterns, the array pattern for an 8 element linear binomial array with λ/2 element spacing and in-phase currents.
(ii) Determine the ratio ET / E0 for = 0 , 45 , 80 and 90 .

(10 Marks) (6 Marks)

Antenna and Radio Wave Propagation (TELC2104)

Page 2 of 4
SITE/September Resit

QUESTION 2 :(30 Marks)
(a) The far-field electric field of an antenna at a point P is given by

E j 60Im sin 5 exp( r)

o

r

where Im is the maximum current along the antenna, r is the distance from the antenna to P, and is the angle to the vertical of a line from the antenna to P.

Determine :

(i) The radiation intensity ( )

(7 Marks)

(ii) For what values of (in the range 0< < ) is the radiation intensity a maximum and what is the corresponding directivity given that the radiation resistance of the antenna is 70 .

(13 Marks)

(b) A uniform linear array consists of 20 vertical dipoles each spaced by /4 with progressive phase shift of .

For the horizontal plane in which the antennas can be considered to be isotropic, determine the phase shift for the following array types:

(i) Broadside (ii) Endfire with maximum at =0 (iii) Endfire with maximum at =180 (iv) For (i) and (ii), determine the directivity.

(2 Marks) (2 Marks) (2 Marks) (4 Marks)

Antenna and Radio Wave Propagation (TELC2104)

Page 3 of 4
SITE/September Resit

QUESTION 3 :(30 Marks)

(a) What are the maximum and minimum distances over which

communication is possible at a frequency of 11 MHz assuming a

single reflection from the F layer of the ionosphere at an electron density maximum of 1.2 x 1012 el m-3 at a virtual reflection height of

280 km?

(15 Marks)

(b) Find the electric field due to surface wave propagation at a frequency of 1 MHz near the Earth's surface at a distance of 90 km from a transmitter radiating 600 W from a vertical quarter wave monopole over ground with relative permittivity r = 12 and conductivity = 5x103 S/m. How much larger in dB would the received electric field strength be without the surface wave attenuation?

The value of the attenuation A can be calculated from

1

A 2 0.3 p sin b p 2 exp 5 p

2 p 0.6 p2

2

8

and the auxiliary parameters are given by x

18 109

0

f

b tan 1 r 1 x
p d cos b x

(15 Marks)

***END OF QUESTION PAPER***

Antenna and Radio Wave Propagation (TELC2104)

Page 4 of 4
SITE/September Resit 