Awp........

Set No. 1

Code No: R05310403

III B.Tech I Semester Regular Examinations, November 2008 ANTENNAS AND WAVE PROPAGATION ( Common to Electronics & Communication Engineering and Electronics & Telematics) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Define and Explain: Directivity and power gain for an antenna. What is the relation between the two? Prove that the directivity of a λ/2 aerial is 0.39 db more than that of short dipole. (b) What are principal planes? How the antenna beam width is defined in such planes? [10+6] 2. (a) Derive an expression for the Radiation Resistance of a Loop Antenna. (b) Find the Effective Length of a Half Wave Dipole. (c) A Small current element at 10MHz produces a radiated field in a direction making angle θ with the element. Assuming that the current is 10 Amp. Calculate the power radiated and radiation resistance of the Antenna.[6+6+4] 3. (a) Derive an expression for radiated power(Rp)of a BSA with ‘n’ vertical dipoles. Plot the Rp in vertical and horizontal planars for a BSA of 4 dipoles. (b) Show the directivity of EFA(with increased directivity) is given by 1.789[4(L/λ)]. [8+8] 4. (a) Derive an expression for electric field of a Non Resonant antenna of length ‘l’ carrying current. (b) Sketch and explain the constructional features of a Helical Antenna.

[10+6]

5. (a) Describe the performance of paraboloids with respect to aperture blocking. (b) Describe the constructional details of cassegrain antennas and sketch its radiation characteristics. [8+8] 6. (a) What is an Optimum Horn? Sketch and Explain its characteristics along with dimensional relations. (b) Explain the first transmission formula and its applicability for antenna gain measurements. [8+8] 7. (a) Explain the following : i. Ground Wave ii. Space Wave iii. Surface Wave. (b) Discuss the characteristics of ionospheric layers. 1 of 2

[8+8]

Set No. 1

Code No: R05310403

8. (a) Space wave propagates between transmitting and receiving stations of heights ‘h1’ and ‘h2’ respectively. Derive the expression for field strength. (b) What are the different paths used for propagating radio waves from 300KHz and 300MHz. [8+8] ⋆⋆⋆⋆⋆

2 of 2

Set No. 2

Code No: R05310403

III B.Tech I Semester Regular Examinations, November 2008 ANTENNAS AND WAVE PROPAGATION ( Common to Electronics & Communication Engineering and Electronics & Telematics) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) The Directivity i. equal to number of point surfaces in the sky that the antenna can resolve. Justify this statement. (b) The field pattern of an antenna is given by En=(Sin θ/θ) (Sin φ/φ) i. Plot the Normalized power pattern. ii. Estimate the main beam efficiency of the antenna.

[8+8]

2. (a) Explain the terms ‘Radiation Field’, ‘Induction Field’ and ‘Electrostatic Field’ by deriving the E Field of a current element through vector potential. (b) What is Polarization? How many types of Polarizations are used in Antennas? Explain. [8+8] 3. (a) Find the radiation Pattern of 4 isotropic elements fed in phase, spaced λ/2 apart by using pattern multiplication. (b) What is uniform linear array? Discuss the application of linear array.

[8+8]

4. (a) Write short notes on “Helical Antenna”. (b) Derive an expression for radiated electric field strength of a traveling wave radiation of length ‘l’. [8+8] 5. (a) What is a parabolic element. How does a parasitic element act when length is greater than and smaller than λ/2. (b) Distinguish between Spherical and Cylindrical paraboloids. Comment on their aperture efficiency and applications. [8+8] 6. (a) What is the principle of equality of path length? How is it applicable to horn antenna? (b) Discuss how the directivity of horn antenna can be measured.

[8+8]

7. (a) What are different mechanisms of propagation of electromagnetic waves? Explain. (b) What is Critical Frequency? What is Virtual Height? Find the maximum distance that can be covered if the virtual height of the ionospheric layer is 250kms. [8+8] 8. (a) Establish the mathematical relation for 1 of 2

Set No. 2

Code No: R05310403

i. Radio Horizon ii. Radius of curvature of array path for LOS waves. (b) Show that the field strength due to space wave given by E = (2E0 /d)sin(2πht hr /λd). ⋆⋆⋆⋆⋆

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[8+8]

Set No. 3

Code No: R05310403

III B.Tech I Semester Regular Examinations, November 2008 ANTENNAS AND WAVE PROPAGATION ( Common to Electronics & Communication Engineering and Electronics & Telematics) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Explain the following : i. ii. iii. iv.

Normalized Field Pattern Beam Solid Angle Beam Efficiency Directivity.

(b) An antenna has a field pattern given by E (θ) =cos θ cos 2 θ for 00 <= θ < = 900 . Find i. the HPBW ii. Beam Width between first nulls. (FNBW)

[8+8]

2. (a) Show that for a slot in a conducting plane, the impedance Zslot is given by Zdipole Zslot =Z0 2 /4 where Z0 is the impedance of free space. (b) The radiation intensity of a particular antenna is given by Ø(θ, Ø) = sin2 θ. Calculate the directivity of the antenna. (c) Define the effective aperture and calculate the effective aperture of 0.25λ dipole. [8+4+4] 3. (a) Enumerate the advantages and disadvantages of linear arrays. (b) Find the phasing required to steer a beam zenith to -400 for a 5 element array with 0.4λ inter element spacing. [8+8] 4. (a) What is meant by Non Resonant antenna? Derive from the first principle, the field due to such antenna and sketch the field pattern for lengths λ and 2λ. (b) Mention the merits and demerits of a traveling wave antenna.

[8+8]

5. (a) A Paraboloid reflector of 1.8m diameter is used at 6GHz. Calculate the beam width between the nulls and gains in dBs. (b) Design Yagi Uda antenna of six elements to provide a again of 12dB if the operating frequency is 200MHz. [8+8] 6. (a) How is the field pattern of a receiving antenna experimentally determined. Explain with a neat diagram. (b) Distinguish between Curved Surface Zoning and Plane Surface Zoning of lens antenna. Discuss their merits and demerits. [8+8] 1 of 2

Set No. 3

Code No: R05310403

7. (a) What is Angle of Tilt? How does it affect the field strength at a distance from the transmitter? (b) A 150m antenna transmitting at 1.2MHz by ground wave has an antenna current of 8A. What voltage is received by a receiving antenna 40kms away, with a height of 2meters? [8+8] 8. (a) A police radio transmitter operating at a frequency 1.69GHz is required to provide a ground wave having a strength of 0.5mv/m at a distance of 16km. The transmitter antenna, having an efficiency of 50% produces a radiating field proportional of cosθ. The ground wave has σ= 5 × 10−5 mho/cm and εr = 15. Calculate the power transmitted. (b) Derive the fundamental equation for free space propagation. ⋆⋆⋆⋆⋆

2 of 2

[8+8]

Set No. 4

Code No: R05310403

III B.Tech I Semester Regular Examinations, November 2008 ANTENNAS AND WAVE PROPAGATION ( Common to Electronics & Communication Engineering and Electronics & Telematics) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Define and account for the presence of i. Radial Power Flow ii. Radiation resistance for a short dipole iii. Uniform Current Distribution. (b) Calculate the following for an antenna carrying 50A (rms) at 480 kHz having effective length of 60.96metres. Take loss resistance of the antenna= 5 Ω. i. ii. iii. iv. v.

Radiation resistance Power radiated Antenna efficiency Directivity and power gain HPBW and BWFN.

[6+10]

2. (a) Define the following terms: i. Directivity ii. Gain iii. Effective Aperture of Antennas. (b) Show that the Directivity of an elementary Dipole (Current Element) is 1.5 or 1.76dB. (c) Calculate the power gain of a half wave Dipole whose ohmic losses and Directive gain are 7.0 Ohms and 1.64 respectively. [6+6+4] 3. (a) Explain the concept of scanning arrays. (b) Show that Dolph-Tchebyshelf distributions gives optimum distribution and minimum side lobe level for a given beam width of major lobe. [8+8] 4. (a) Distinguish between i. Resonant and Non Resonant antennas. ii. Narrow Band and Wide Band antennas. (b) Show that a single wire excited with a traveling wave current is an end fire antenna with a sharp null along the direction of extension of the wire. [8+8] 5. (a) A paraboloid reflector has radiation characteristics whose HPBW is 50 . Find out its null to null beam width and power gain. 1 of 2

Set No. 4

Code No: R05310403

(b) Discuss the conditions under which a parasitic dipole placed near and parallel to a driven dipole can act as a reflector. [8+8] 6. (a) With a neat setup, explain the method of measurement of the beam width of pyramidal horn antennas in E-plane. How does it differ from H-plane measurement? (b) Explain the basic principle of operation of lens antenna.

[8+8]

7. (a) Discuss the propagation characteristics of EM wave. (b) Mention the salient features of Ground wave propagation.

[8+8]

8. (a) Derive an expression for the curvature of the ray path due to the changing refractive index in the troposphere. (b) Explain the phenomenon of duct propagation. ⋆⋆⋆⋆⋆

2 of 2

[8+8]