Set No. 1
Code No: RR310402
in
III B.Tech I Semester Supplimentary Examinations, November 2008 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.
ld .
(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]
2. (a) Explain the terms Poynting vector, Impedance of free space and bring out their relation with radiation fields of an antenna.
[8+8]
uW
i. an isotropic case, ii. a half wave dipole.
or
(b) Show that the rms field strength from an antenna with gain G, radiating P 1/2 watts of power is given by, E = (30PG) Volts / mts. in free space. Find E at r a distance of 1km., if the radiated power is 1kW for
3. Evaluate the radiation characteristics -HPBW, Nulls, side lobe positions md actual side lobe levels, for a uniform linear array of 10 elements with quadrates -wave . Sketch the pattern. What happens if α is length spacing (d), fed with α = 2πd λ − π/10? [12+4] changed to α = −2πd λ 4. (a) For a traveling wave wire antenna of length L, obtain the expression for vector potential, assuming suitable current distribution.
nt
(b) Examine the effect of variation of length L on the radiation patterns of i. standing wave radiators. ii. non resonant wire radiators.
[8+8]
Aj
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) What is the need for flaring in conventional wave guides? Hence explain the geometry of a pyramidal horn with neat sketches in E and H plane crosssections, and obtain an expression for its directivity. (b) Explain and distinguish between short focal length lenses, long focal length lenses and stepped lenses. Which of them are preferred and why? [8+8] 7. (a) Describe the structure of the ionosphere and the part played by each layer in it in the long distance transmission of radio signals in the HF band. 1 of 2
Set No. 1
Code No: RR310402 (b) Explain the phenomena of wave tilt and its effects.
[10+6]
8. (a) Discuss the effect of curvature of earth over space wave propagation. (b) Explain the significance of the forms: i. Standard atmosphere, and ii. modified refractive radix.
Aj
nt
uW
or
⋆⋆⋆⋆⋆
ld .
in
(c) Calculate the power density reaching the moon’s surface from a 1MW pulse transmitter located on the earth. The antenna gain is 55 db. Take the distance between the moon and the earth is 4,00,000 Km. Assume that transmission medium is loss less. [6+4+6]
2 of 2
Set No. 2
Code No: RR310402
1. (a) Explain and distinguish between the terms:
ld .
i. E plane and H Plane. ii. vertical and horizontal planes. iii. Beam area, beam efficiency and resolution.
in
III B.Tech I Semester Supplimentary Examinations, November 2008 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 ⋆⋆⋆⋆⋆
(b) For a λ/4 monopole carrying sinusoidal current Imax , sketch the radiation pattern and find its HPBW and directivity. [7+9]
or
2. Sketch and comment on the current distributions and the principal plane patterns , 2λ. List out the lef f , D, HPBW and Ae for of vertical antennas of length λ2 , λ, 3λ 2 the first two types of antennas, and compare. [16]
uW
3. (a) Compare the radiation characteristics of BSAs, EFAs, EFAs with increased directivity, and Binomial arrays. Under what conditions they are preferred? (b) What are the conditions for the linear array of 20 isotropic elements to radiate in end fire, broad side modes, and Hansen-word yard array mode? [8+8] 4. (a) Explain the constructional features and radiation characteristics of a Rhombic Antenna. (b) Explain how parasitic elements are used as directors and reflectors. What is the need for such elements? [8+8]
nt
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.
Aj
(b) With a neat sketch, explain the image formation and field calculation for the case of a 600 corner reflector. [10+6]
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. Write short notes on (a) Maximum usable frequency (b) Virtual hight 1 of 2
Set No. 2
Code No: RR310402 (c) Wave-tilt (d) Alternation in Ionosphericlayers (e) Multi-hop Transmission
[3+3+4+3+3]
in
8. List out the modes of propagation and their frequency ranges for ratio waves. Show that an approximate estimate for the magnitude of electric field strength at VHF and above is given by 240Iπh1 h2 v/m λd2
Aj
nt
uW
or
⋆⋆⋆⋆⋆
ld .
where I - current in the λ/2 transmitting aerial h1 ,h2 - heights of Tx and Rx antennas d - direct distance between aerials λ - wavelength. Specify the assumptions made for the validity of the above expression.
2 of 2
[16]
Set No. 3
Code No: RR310402
in
III B.Tech I Semester Supplimentary Examinations, November 2008 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 ⋆⋆⋆⋆⋆
ld .
1. (a) State and explain reciprocity theorem. Explain how this theorem can be applied to the case of a pair of parallel dipoles. (b) Establish the relations between directivity and effective area, directivity and effective length. [8+8]
uW
or
2. Starting with the expression Idl for a current element, show that the phasor expression for vector potential and field strengths will be Az = µIdl e−jβr 4πr −jβr 1 jβ+ Hϕ = Idlsinθe 4πr r −jβr 1 1 jβ+ Eθ = ηIdlsinθe + 2 4πr r jβr ηIdlcosθe−jβr 2 2 Er = + 2 4πr r jβr p whereβ = ω/ν = 2π/λ, η = µ/ ∈ [8+8]
3. (a) Show that the directivity can be improved by using a number of antennas in any broad side or end fire array. (b) Prove that the level of secondary lobe is -13.5 dB below that of major lobe in an uniform linear array. [6+10] 4. (a) With neat schematics, describe the principle of working of a 3 element yagi antenna, listing out its length and spacing requirements.
nt
(b) Sketch the current distributions on a folded dipole, and account for its input impedance when the two legs have unequal diameters. [8+8]
Aj
5. (a) Sketch and explain the constructional features of a helical antenna. Distinguish between axial and normal modes of helix radiations and list out their requirements. (b) Explain the characteristics of an active square corner reflector with the help of image principle. [10+6]
6. (a) Explain the method of measurement of radiation pattern and beam width of an antenna in any one principal plane, with a neat set up. (b) Explain the principle of zoning in lenses, and obtain an expression for the step size of such lenses. What are its merits and demerits? [8+8] 7. (a) Describe the structure of the ionosphere and the part played by each layer in it in the long distance transmission of radio signals in the HF band. 1 of 2
Set No. 3
Code No: RR310402 (b) Explain the phenomena of wave tilt and its effects.
[10+6]
8. (a) Discuss the phenomenon and effect of the reflection of radio waves by earth’s surface.
in
(b) Explain the principle of operation of terrestrial line of sight communication. [8+8]
Aj
nt
uW
or
ld .
⋆⋆⋆⋆⋆
2 of 2
Set No. 4
Code No: RR310402
in
III B.Tech I Semester Supplimentary Examinations, November 2008 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 ⋆⋆⋆⋆⋆
ld .
1. (a) From the knowledge of Directive gain ‘gd ’, Prove the following relation. 2 le 2 gd = 120π Where le = effective length of the antenna Rrad λ Rrad = Radiation resistance of the antenna. and state the importance of this relation.
(b) A source has bidirectional power pattern with a radiation intensity of U = 4 sin θ. Find its directivity and HPBW, sketching the pattern. [8+8]
or
2. (a) Define and account for the presence of i. Radial power flow ii. Radiation resistance for a short dipole, iii. Uniform current distribution
uW
(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) Compare the radiation characteristics of Uniform Linear Arrays, fed withi. Uniform amplitudes ii. Triangular taper amplitudes iii. Binomially tapered amplitudes.
nt
(b) list out the mathematical relations for a N element half-wavelength spaced binomial array. Hence, find the directivity, HPBW for N=20 case. What is the expression for its field pattern? [10+6]
Aj
4. (a) Distinguish between a simple λ/2 dipole and folded dipole, clearly accounting for the merits and demerits. (b) What are traveling wave antennas? Explain the features and characteristics of a terminated negative antenna. [8+8]
5. (a) Draw the different shapes of small loop antennas and explain its operation by drawing the radiation pattern. (b) List out the conditions broadside and end fire type of modes of operations are possible helical antennas. Compare their patterns and characteristics. [6+10]
6. (a) Distinguish between sectoral, Pyramidal and Conical Horns, with neat sketches. List out their utility and applications. 1 of 2
Set No. 4
Code No: RR310402
(b) With neat set up, explain the absolute method of measuring the gain of an antenna. [8+8] 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?
in
(b) Describe any two types of fading normally encountered in radio wave propagation. How are the problems of fading overcome? [8+8]
Aj
nt
uW
or
⋆⋆⋆⋆⋆
ld .
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]
2 of 2
