Awp Nov07

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Set No. 1

Code No: RR310402

III B.Tech I Semester Supplimentary Examinations, November 2007 ANTENNA 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 ⋆⋆⋆⋆⋆

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1. Calculate the following for an antenna carrying 50A (rms) at 480kHz having effective length of 60.96metres. Take loss resistance of the antenna= 5Ω (a) Radiation resistance

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(b) Power radiated. (c) Antenna efficiency.

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(d) Directivity and power gain.

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(e) HPBW and BWFN.

2. (a) Define and account for the presence of

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i. Radial power flow ii. Radiation resistance for a short dipole, iii. Uniform current distribution

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(b) Obtain the relative amplitudes of radiation, induction and electro-static fields at a distance of 2λ from a short current element having an uniform current of 1 mA along its length. [8+8] 3. (a) What is array factor? Find the array factor of two element array?

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(b) For an array of two identical infinitesimal dipoles oriented with a separation of D and phase excitation difference B between the elements, find the angles of observation where the nulls of the array occur. The magnitude of excitation of the elements is same. [8+8] 4. (a) Compare the requirements and radiation characteristics of resonant and nonresonant radiators? (b) Determine the lengths and spacing requirements for a 3-element Yagi -Uda antenna array at 500 mHz, and explain its characteristics. [6+10] 5. (a) Establish and explain the gain and beam width relations for a parabolic reflector and account for its beam shaping considerations. (b) Write short notes on: Cassegrainian antennas.

[8+8]

6. (a) Distinguish between sectoral, Pyramidal and Conical Horns, with neat sketches. List out their utility and applications.

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Set No. 1

Code No: RR310402

(b) With neat set up, explain the absolute method of measuring the gain of an antenna. [8+8] 7. (a) Account for the type of propagation and the associated characteristics for medium wave radio broadcast signals. (b) Define and distinguish between the terms: MUF, LUHF, Optimum frequency. [8+8] 8. (a) Explain the wave propagation for signals in microwave frequency range. T

i. small d and ii. Large d.

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(b) Two antennas operating in the frequency range 300 MHz - 3000 MHz are erected at heights h1 and h2 on the surface of the earth which is assumed to be flat and conducting. The separation between the antennas is d. Derive an expression for the attenuation function F such that ER (Received field)=free space field × F. Sketch the variation of ER with distance, for

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[6+10]

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Set No. 2

Code No: RR310402

III B.Tech I Semester Supplimentary Examinations, November 2007 ANTENNA 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 Reciprocity theorem and prove it in case of an Antenna system.

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2. (a) Define and account for the presence of

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(b) Show that for a Hertzian dipole, the aperture area is 0.12 λ2 and for a halfwave dipole, it is 0.13 λ2 and for an isotropic radiator, it is 0.08 λ2 . Explain the relation used. [8+8]

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i. Radial power flow ii. Radiation resistance for a short dipole, iii. Uniform current distribution

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(b) Obtain the relative amplitudes of radiation, induction and electro-static fields at a distance of 2λ from a short current element having an uniform current of 1 mA along its length. [8+8]

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3. (a) An array consists of three collinear λ/2 dipoles with λ spacing. Determine gain and beam width of the major lobe between 3 dB points in the plane containing the array.

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(b) Explain the significance and characteristics of an EFA with increased directivity. [10+6]

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4. (a) Explain the constructional features and distinguish between unidirectional and bi directional V antennas. (b) Discuss the characteristics, merits and demerits of a folded dipole, with and with out parasitic elements. [8+8] 5. (a) Establish and explain the gain and beam width relations for a parabolic reflector and account for its beam shaping considerations. (b) Write short notes on: Cassegrainian antennas.

[8+8]

6. (a) Explain the first transmission formula and its applicability for antenna gain measurements. (b) Explain the significance, merits and demerits of zoning in lens antennas.[8+8] 7. (a) Discuss the importance of ground wave propagation for communication purposes. Why ground waves are not received beyond certain range. Explain the phenomenon. (b) Establish the effects of D-layer in sky wave propagation. 1 of 2

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[10+6]

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Set No. 2

Code No: RR310402 8. (a) Establish the mathematical relations for: i. Ratio horizon, ii. radius of curvature of array path for los waves

(b) Explain the significance of flat earth and curved earth considerations for tropospheric wave propagation. [5+5+6]

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Set No. 3

Code No: RR310402

III B.Tech I Semester Supplimentary Examinations, November 2007 ANTENNA 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 ⋆⋆⋆⋆⋆

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1. (a) Define the term input “impedance” of an antenna. Show that the input impedance of an antenna used in a transmitting mode is the same as the input impedance if it is used in receiving mode. Clearly mention the assumptions made in proving this relation.

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2. (a) Define and account for the presence of

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(b) Define and derive a relation for effective length ‘le’ of an antenna. Find ‘le’ or a short dipole antenna. [8+8]

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i. Radial power flow ii. Radiation resistance for a short dipole, iii. Uniform current distribution

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(b) Obtain the relative amplitudes of radiation, induction and electro-static fields at a distance of 2λ from a short current element having an uniform current of 1 mA along its length. [8+8]

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3. (a) A linear broad side array consists of four equal in phase point sources with λ/3 spacing. Calculate and plot the field pattern. Also find directivity and beam width.

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(b) Distinguish between ordinary EFA and an EFA with increased directivity and compare them. [10+6] 4. (a) Compare the requirements and radiation characteristics of resonant and nonresonant radiators? (b) Determine the lengths and spacing requirements for a 3-element Yagi -Uda antenna array at 500 mHz, and explain its characteristics. [6+10] 5. (a) Establish and explain the gain and beam width relations for a parabolic reflector and account for its beam shaping considerations. (b) Write short notes on: Cassegrainian antennas.

[8+8]

6. (a) Distinguish between sectoral, Pyramidal and Conical Horns, with neat sketches. List out their utility and applications. (b) With neat set up, explain the absolute method of measuring the gain of an antenna. [8+8] 7. (a) Describe the effect of terrain and earth’s curvature on ground wave propagation. 1 of 2

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Set No. 3

Code No: RR310402 (b) Explain the terms

i. Virtual height and ii. Multihop transmission iii. sporadic E layer with reference to sky wave propagation.

[6+10]

8. With neat diagrams, explain the important features of different types of space wave propagation of electromagnetic waves over long distance even beyond the horizon. For what frequency range this is applicable and why? [16]

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Set No. 4

Code No: RR310402

III B.Tech I Semester Supplimentary Examinations, November 2007 ANTENNA 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) As related to antennas, define and explain the following terms:

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Gain directivity radiation resistance effective area effective length efficiency beam width bandwidth.

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i. ii. iii. iv. v. vi. vii. viii.

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(b) Evaluate the directivity of

i. an isotropic source, and ii. source with bi-directional cos θ power pattern.

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2. (a) Define and account for the presence of

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i. Radial power flow ii. Radiation resistance for a short dipole, iii. Uniform current distribution (b) Obtain the relative amplitudes of radiation, induction and electro-static fields at a distance of 2λ from a short current element having an uniform current of 1 mA along its length. [8+8] 3. (a) What is array factor? Find the array factor of two element array? (b) For an array of two identical infinitesimal dipoles oriented with a separation of D and phase excitation difference B between the elements, find the angles of observation where the nulls of the array occur. The magnitude of excitation of the elements is same. [8+8] 4. Write notes on: (a) Parasitic elements and their reference (b) Terminated antennas (c) Applications of Rhombic Antenna. (d) Multi director Yagi Antenna.

[4+4+4+4] 1 of 2

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Set No. 4

Code No: RR310402

5. (a) Sketch the typical geometry of a helical antenna radiating in axial mode, and list out all its parameters and basic characteristics. List out the expressions for HPBW, BWFN, directivity and axial ratio. (b) With a neat sketch, explain the image formation and field calculation for the case of a 600 corner reflector. [10+6] 6. (a) Determine the axial length, H-plane aperture dimension and the total flare angles in E and H 0.35λ. Calculate its beam widths and directivity. (b) List out and explain the set of principal plane patterns required for a circularly polarized antenna. [8+8]

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7. (a) For vertical incidence, determine the critical frequency for reflection by the ionosphere if maximum value of electron density is 1.24 x 106 /cc. What happens if the angle of incidence is changed to 600 Establish the relations used?

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(b) Describe any two types of fading normally encountered in radio wave propagation. How are the problems of fading overcome? [8+8]

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8. With neat diagrams, explain the important features of different types of space wave propagation of electromagnetic waves over long distance even beyond the horizon. For what frequency range this is applicable and why? [16]

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2 of 2

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