ANTENNAS AND WAVE PROPAGATION--Question Bank

ECE Department Question Bank
Subject Name : ANTENNAS AND WAVE PROPAGATION                       Branch:ECE Subject Code  : 10144EC604                                                             Year / Sem. : III/VI
Unit – I
Part - A
1	Define retarded vector potential.
2	Define radiation resistance of an antenna.
3	Calculate the radiation resistance of a λ/10 wire dipole in free space.
4	An antenna whose radiation resistance is 300 ohm operates at a frequency of 1 GHz     and with a current of 3Amp.Find the radiated Power.
5	What is meant by oscillating electric dipole?
6	Distinguish between induction field and radiation field.
7	State the differences between half wave dipole and quarter wave monopole.
8	Define: Electric vector potential.
9	A short vertical transmitting antenna erected on the surface of a perfectly      conducting earth produce an rms field strength Eө=100sinӨ mv/m at a distance of      1km from the antenna.calculate the total power radiated by the antenna.
10	Define antenna efficiency
11	Define Hertzian dipole.
	Part - B
11	a)Derive an expression for the power radiated and radiation resistance of a small           current element.  (8) b) At what distance in wavelength, is the radiation component of magnetic field       be equal and twice the induction component.     (8)
12	a)When the amplitude of the magnetic field in a plane wave is 2A/m.      i) Determine the magnitude of the electric field for the plane wave in free space.      ii) Determine the magnitude of the electric field when the wave propagates in a medium which is characterized by σ =0, µ= µ0 and ε = ε0                                                   (8)        b) Derive an expression for the radiation field from an infinitesimal Dipole       and also write the expressions for far field and near field regions    (8)
13	a)Derive an expression for the radiation field from a half wave dipole            (10) b) A dipole antenna with length equal to 10cm and carrying a current of 1A at a          frequency of 108 /2π hertz radiates into free space. Calculate the electric field          intensity at a distance of r=10km from the antenna, where the induction field is           negligible.                                                                                                            (6)
14	a)      Explain retarded vector potential.                                                (4)       b)   A plane electromagnetic wave having a frequency of 100 MHz has an averaging pointing vector of 1 W/m2.If the medium is lossless with relative permeability 2 and relative permittivity 3. Find i) velocity of propagation. ii) Wavelength.                                  (12)
15	a)      Derive an expression for the radiation field from a small current element  (8) b)      A half wave dipole is radiating into free space. The co-ordinate system is defined so that the origin is at the center of the dipole and the Z axis is aligned with the dipole. Input power to the diploe is 100W.Assuming an overall efficiency of 50%, find the power density (in w/m2) at r=500m, θ=60,φ=0.                                                      (8)
16	a)An antenna whose radiation resistance is 300 ohm operates at a frequency of 1 GHz and with a current of 3 amps. Find the radiated power.                                                   (3) b)A half wave dipole with a total loss resistance of 1Ω, is connected to a generator whose internal impedance is 50+j25 Ω. Assuming that the peak voltage of the generator is 2 V and the impedance of the dipole excluding the loss resistance is 73+j42.5 Ω, find the power supplied by the source.                                                                                                        (3) c) What do you mean by induction field and radiation field?                         (5) d) Find the radiation resistance of a hertizian dipole of length λ/40, λ/60, and λ/80.   (5)

Unit – II
Part - A
1	Distinguish between broadside array and end fire array.
2	Define Ferrite loop.
3	An antenna has a radiation resistance of 72 ohm. A loss resistance of 8 ohm and power  gain of 12 db. Determine the antenna efficiency and directivity.
4	What is the maximum effective aperture of a microwave antenna with a directivity of 900?
5	A linear broadside array consists of 4 equal isotropic in phase, point source with   λ /3 spacing. Calculate the directivity, beam width and HPBW.
6	State the reciprocity theorem for two antennas.
7	Define array factor.
8	What are grating lobes?
9	An antenna with omni directional amplitude pattern with a half power beam width of 90 degrees has radiation intensity of U=sinnq.Determine the value of ‘n’
10	State pattern multiplication
11	Define radiation intensity
12	Mention the two important advantages of folded dipole antenna
13	Give the significance of Friss transmission formula.
	Part - B
1	a. Calculate the field for an array of two isotropic sources of same amplitude           and phase for d=3l/4.                                                                                   (8)  b. The radiation intensity of an antenna is given by U (q,F) = {B0 sinq sin2F     , where 0£F£p, 0£F£p        0                          , elsewhere.                                (8)                 Determine the maximum directivity
2	a.  Derive an expression for radiated field due to small circular loop              antenna.                                                                                                       (10)           b. Derive an expression relating directivity, gain and effective length.              (6)
3	a. Show that the relative E (F) pattern of an array of two identical isotropic in               phase point sources are arranged in fig 1.is given by E (F) = cos [dr/2 sin F               where dr=2pd/l.                                                                                          (8)     b. In a microwave communication link, two identical antennas operating at 10             GHz are used with power gain of 40 db. If the transmitted power is 1 W. Find             the received power, if the range of the link is 30 km.                                          (8)
4	.     a. Explain the operation of helical antenna in normal mode of operation.        (8) b. A uniform linear array consists of 16 isotropic point sources with a spacing of     l/4, if the phase difference d= -90 degrees. Calculate i) HPBW ii) Beam solid     Angle iii) Effective aperture iv) Directivity.                                                   (8)
5	a) For an array of 2 isotropic point sources, fed with currents of same magnitude but, in phase quadrature, determine the radiation pattern. Evaluate the null directions and directions of maxima and draw the pattern.                                                                                  (10) b) Explain the principle of pattern multiplication with an example.                        (6)
6	Derive  the formula to find the maxima, null points and half power points of an N element broadside  array and show that the first minor lobe is 13.46 dB down from the major lobe.(16)

Unit – III
Part - A
1	Draw the log periodic structure at UHF and VHF ranges.
2	What is the effect of decreasing α in log periodic antenna?
3	State Huygen’s Principle.
4	Draw the structure of 3 element Yagi-Uda antenna and give the dimensions and             spacing between the elements.
5	What are the methods of feeding slot antennas?
6	Why log periodic antenna called so?
7	State induction theorem.
8	What is the reason for feeding from end with shorter dipoles in LPDA?
9	Calculate the directivity of an optimum horn antenna with a square aperture of    10 λ on a side.
10	What is the use of travelling wave antennas?
11	What is the type of radiation pattern produced when a wave travels in a wire?
12	Design a rhombic antenna to operate at a frequency of 20 MHz with the angle of elevation 30 degree with respect to ground.
13	Design a 3 element Yagi-Uda antenna to operate at a frequency of 172MHz.
14	Design a log periodic dipole array to operate at frequencies from 100 to 500 MHz with    4 elements. Give i) Length of the longest element        ii) Gain
15	Why yagi-uda antenna is called ‘super directive’?
	Part - B
1	(a).i) Derive the expression for far field components of a rectangular aperture                   on an infinite ground plane.                                                                   (10)             ii)  Write short notes on Yagi Uda antenna.                                                               (6)                                                             (OR)   (b).i) Draw the Structure of log-periodic array and explain its working Principle.   (4)                 ii) Derive the parameters that describe the configurations of LPDA.                            (4)           iii) Derive the expression for radiation from the open end of coaxial cable.          (8)
2	a) Design a rhombic antenna for an elevation angle α=17.5 degree.                  (8) b) Explain the working principle of rhombic antenna .                                      (8)
3	a) Design a Yagi-Uda six element antenna for operation at 500 MHz with     a folded dipole feed.     i) What are the lengths of the reflector element, driven element?    ii) What is the spacing between reflector and driven element?                     (8) b) What is the need for transposing the lines in log periodic antenna?               (4)  c) A monofilar axial mode helical antenna has 30 turns, λ/3diameter and λ/5 spacing.     Find i) HPBW ii) gain                                                                                 (4)
4	a)   Derive the relation between dipole and slot impedances.                                     (6) b) Explain the construction and working of rhombic antenna and derive the                 expressions for design equations.                                                                         (10)
5	a)  Determine the length, H-plane aperture, flare angles θE and θH of a pyramidal                                 horn antenna for which the E plane aperture aE=10λ.The horn is fed by                                                  rectangular with TE10 mode. Assume δ=0.2 λ for E plane and δ=0.375λ for H                            plane. Find half power beam widths and directivity.                                         (8)        b) Explain the features and working principle of Horn antenna. How is the         antenna fed and what are its applications?                                                         (8)
6	a)Draw a neat sketch of helical antenna and explain its principle.                  (8)              b) Draw the structure of log periodic antenna and explain its working        principle.

Unit – IV
Part - A
1	How spherical waves obtained from biconical antenna?
2	State Babinet’s Principle.
3	What is the H plane metal plate lens?
4	What are the disadvantages of lens antenna?
5	What are the applications of slot radiator?
6	State the field equivalence principle.
7	A paraboloid reflector is required to have a power gain of 1000 at a frequency of 3 GHz. Determine the beam width and mouth diameter of the antenna.
8	Find the diameter of paraboloid reflector antenna required to produce a null beam width of 10 degree at 3 GHz.
9	Find the power gain in dB of a paraboloidal reflector of open mouth aperture 10 λ.
10	A parabolic dish provides again of 75dB at a frequency of 15GHz. Calculate the capture area of the antenna its 3dB and null beam widths.
11	Calculate the beam width between first nulls of a 2.5m paraboloid reflector used at 6GHz. What will be its gain in dB?
12	Calculate the physical area of the loop and compare it with its maximum effective aperture if the radius of the small loop of constant current is l/25.
	Part - B
1	a) Derive the expression for radiation from Huygens’s source                           (8) b) Write short notes on biconical antenna.                                                          (8)
2	a) A paraboloid reflector is required to have a power gain of 1000 at a             frequency of 3 GHz. Determine the beam width and mouth diameter of the             antenna.                                                                                                             (6)  b) List different types of lens antenna and their uses.                                         (4)  c) What is meant by spill over in parabolic reflector? State the effect of        aperture number on spill over.                                                                     (6)
3	a) Discuss the different methods of feeding parabolic reflector?                            (8) b) Explain how E plane type metal plate lens antennas are developed and derive the expressions for spacing between the plates and equation of ellipse.                                           (8)
4	a)Derive the expressions for far field components of a rectangular aperture on an infinite ground plane.                                                                                                                               (8) b) Find the total beamwidth and first null beamwidth and half power beamwidth.                                                                                                                                                                                 (8)
5	a) Derive ht edesign equation of the horn antenna and half power beamwidths. How will you find directivity and power gain of the horn antennas?                                                           (8) b)Whatis a slot radiator? Explain it.                                                                                      (8)
6	Explain th e parabolic reflector type  antenna with cassegrain feed. Also mention its advantages and disadvantages.                                                                                           (16)

Unit – V
Part - A
1	Define skip distance.
2	Explain Duct propagation.
3	Assume that reflection takes place at a height of 400km and that the maximum density in the ionosphere corresponds to a 0.9 refractive index at 10MHz. what will be the range for which the MUF is 10MHz?(assume flat earth)
4	What is the critical frequency for reflecting at vertical incidence if the maximum value of electron density is 1.24x106cm-3?
5	A high frequency radio link has to be established between two points on the earth 200km away. The reflection region of the ionosphere is at a height of 200km and has a critical frequency of 6MHz. calculate the MUF for the given path.
6	What is known as diversity reception?
7	What are the factors that affect the propagation of radio waves?
8	Define gyro frequency.
9	Define critical frequency.
10	What is maximum usable frequency?
11	State the relation between critical frequency and electron density of an ionospheric layer.
	Part - B
1	a)Write short notes on            MUF            Diversity reception            Fading            Critical frequency                                                                                          (8) b) Find the effective dielectric constant and refractive index of an ionized        region.                                                                                                                    (8)
2	a)  Calculate the field strength for ground wave propagation.                   (4) b) Explain the mechanism of refraction from Ionosphere.                         (6)  c) What is the effect of earth’s magnetic field in Ionosphere region?        (6)
3	Explain in detail about ionospheric propagation                                           (16)
4	Explain the advantages of troposperic wave propagation and skywave propagation. Explain the limitations of ground wave propagation.
5	Draw the profile diagram of Ionosphere and explain.                    (8) Explain th echaracteristics of Ionosphere.                                       (8)
6	a) The observed critical frequencies of E and F layer at a particular time are 2.5MHz and 8.4MHz. Calculate the maximum electron concentrations of the layer.          (4) b) Derive the expression for the refractive index of the  ionosphere.              (12)