code no: r10 antennas and wave propagation · pdf fileiii b.tech i semester supplementary...

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III B.Tech I Semester Supplementary Examinations, May/June - 2015

ANTENNAS AND WAVE PROPAGATION

(Electronics and Communication Engineering)

Time: 3 hours Max. Marks: 75

Answer any FIVE Questions

All Questions carry equal marks

*****

1 a) Define the various Antenna Parameters? 8

b) Explain the current distribution on a thin wire antenna. 7

2 Based on field equations (both E and H) from current element, define the terms

Radiation, Induction and Electrostatic field.

15

3 a) What are the advantages and disadvantages with array technique in antenna system? 5

b) Derive the array-factor of 2-element array antenna? 10

4 a) List out the differences between resonant and non-resonant antennas? 5

b) Explain the working principle of Rhombic Antenna? 10

5 a) What is a folded dipole antenna? Why it is better than dipole antenna? Explain. 8

b) Explain the working principle of N-element Yagi-Uda Antenna? 7

6 a) Explain the working principle of Len’s Antennas? 8

b) Find the HPBW, power gain and directivity of a horn whose dimensions are 12cmx6cm

at a frequency of 7GHz.

7

7 a) Explain the types of propagation of Radio waves? 5

b) A broad cast transmitter supplies 80KW to an antenna that radiates 75% of this power.

The antenna has directional characteristic 1.28.Find the field strength of the ground wave

at 10km at 500KHz. Relative permittivity is 9 and σ =10-4

mho/cm.

10

8 a) Explain the effect of earth’s curvature on tropospheric wave propagation. 8

b) If the critical frequency of an ionized layer is 1.75MHz. Find the electron density of the

layer?

7

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Code No: R31045 Set No. 1 R10

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*****

1 a) Explain Radiation mechanism from single wire and 2-wire antenna? 8

b) Find the directivity and efficiency of an antenna if its Rr=80Ω, RL=20 Ω, power gain is

10dB and antenna operates at a frequency of 100MHz?

7

2 Prove that the radiation resistance of an half-wave dipole is 73Ω?

15

3 a) Define the types of array antennas? 5

b) Derive the array factor and draw the radiation pattern of 2-element broadside array

antenna with d=1λ

10

4 a) Explain the working principle of Inverted-V antenna? 8

b) Design a Rhombic antenna to operate at 20MHz when the angle of elevation is 10deg.

7

5 a) Explain the construction, merits and demerits of a Cassegrain antenna? 8

b) Design a three element Yagi-Uda antenna to operate at a frequency of 25MHz?

7

6 a) Explain the types of horn antennas? 8

b) The aperture dimensions of a pyramidal horn are 8cmx4cm, operating at a frequency of

10GHz. Find the beam width, and directivity.

7

7 a) Explain the ionospheric abnormalities on wave propagation. 8

b) Find the roughness of earth, if σs is 100m, incident angle is 300 and operating frequency

is 1MHz.

7

8 a) Explain the LOS distance of spacewave propagation? 7

b) Define i) critical angle ii)Optimum working Frequency 8

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*****

1 a) Prove that Leff(Transmitting ) = Leff(Receiving) [8]

b) If the transmitting power from an isotropic antenna is 10KW, find the power density at

distances of 10km and 50km.

[7]

2 What is a small loop antenna? Derive the radiation fields from electrically small loop

antenna?

[15]

3 a) In array antenna, discuss about advantages, disadvantages and limitations with

multiplication pattern technique?

[8]

b) By using pattern multiplication technique, Draw the radiation pattern of 4-element

array antenna?

[7]

4 a) Explain the working principle of Helical antenna in normal mode. [7]

b) Explain the design parameters of a Rhombic antenna.

[8]

5 a) Briefly explain types of corner reflector antennas? [8]

b) For what mouth diameter and capture area of a paraboloid reflector is a BWFN of 5deg

obtained when it is operated at 2GHz?

[7]

6 a) With neat diagram, explain Antenna gain Measurement technique? [10]

b) Explain the zoning concept in lens antenna.

[5]

7 a) Write short notes on i)Skip Distance ii)MUF [8]

b) Explain the effect of ionospheric absorption on wave propagation.

[7]

8 a) Derive field strength due to space-wave propagation? [8]

b) Find the maximum distance that can be covered by a space wave when the antenna

heights are 70m and 40m.

[7]

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1 a) Define Effective Height (for different current distributions) and Effective aperture of an

antenna.

[8]

b) Calculate the effective area of a half-wave dipole operating at 500MHz, if the efficiency

of an antenna is 85%.

[7]

2 a) List out the similarities and differences between alternating current element and loop

antenna.

[8]

b) Find the radiation resistance of a loop antenna of diameter 0.5m operating at 1MHz?

[7]

3 Derive the parts of radiation pattern of N-element Uniform array.

[15]

4 a) Explain i) axial-ratio ii) types of polarizations in helical antenna. [8]

b) If a helical antenna has spacing between turns 0.05m, diameter 0.1m, number of turns

20 and operates at 10MHz. Find HPBW and directivity?

[7]

5 a) Derive the array factor of 90deg corner reflector antenna. [8]

b) A paraboloid reflector operates at a frequency of 8GHz and it provides a power gain of

50dB. Find the capture area?

[7]

6 a) Explain the working principle of dielectric lens antenna. [7]

b) What are the various methods of measuring antenna gain? Explain any one. [8]

7 a) Explain in detail about ionospheric abnormalities? [8]

b) Find out the relative permittivity of D- layer (400electrons/cm3) and E-layer (4x10

5

electrons/cm3) of the ionosphere for an EM wave of frequency 45 MHz.

[7]

8 a) Explain Duct propagation? [7]

b) A communication system is to be established at a frequency of 50MHz with a

transmitter power of 1Kwatt. The field strength the directive antenna is 3 times that of a

half-wave antenna. If ht=50m and hr=10m, A field strength of 600mv/m is required to

give satisfactory reception. Find the range of the system?

[8]

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code no: r10 antennas and wave propagation · pdf fileiii b.tech i semester supplementary...

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