PIT ECE VI SEM
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PIT ECE VI SEM
EC6602 ANTENNA AND WAVE PROPAGATION L T P C 3 0 0 3
OBJECTIVES:
•
To give insight of the radiation phenomena.
•
To give a thorough understanding of the radiation characteristics of different types of antennas
•
To create awareness about the different types of propagation of radio waves at different
Frequencies
UNIT I FUNDAMENTALS OF RADIATION 9
Definition of antenna parameters – Gain, Directivity, Effective aperture, Radiation Resistance, Band width, Beam width, Input Impedance. Matching – Baluns, Polarization mismatch, Antenna noise temperature, Radiation from oscillating dipole, Half wave dipole. Folded dipole, Yagi array.
UNIT II APERTURE AND SLOT ANTENNAS 9
Radiation from rectangular apertures, Uniform and Tapered aperture, Horn antenna , Reflector antenna , Aperture blockage , Feeding structures , Slot antennas ,Microstrip antennas – Radiation mechanism – Application ,Numerical tool for antenna analysis
UNIT III ANTENNA ARRAYS 9
N element linear array, Pattern multiplication, Broadside and End fire array – Concept of Phased arrays, Adaptive array, Basic principle of antenna Synthesis-Binomial array
UNIT IV SPECIAL ANTENNAS 9
Principle of frequency independent antennas –Spiral antenna, Helical antenna, Log periodic. Modern antennas- Reconfigurable antenna, Active antenna, Dielectric antennas, Electronic band gap structure and applications, Antenna Measurements-Test Ranges, Measurement of Gain, Radiation pattern,
Polarization, VSWR
UNIT V PROPAGATION OF RADIO WAVES 9
Modes of propagation , Structure of atmosphere , Ground wave propagation , Tropospheric propagation , Duct propagation, Troposcatter propagation , Flat earth and Curved earth concept Sky wave propagation – Virtual height, critical frequency , Maximum usable frequency – Skip distance,
Fading , Multi hop propagation
TOTAL: 45 PERIODS
OUTCOMES:
Upon completion of the course, students will be able to:
Explain the various types of antennas and wave propagation.
Write about the radiation from a current element.
Analyze the antenna arrays, aperture antennas and special antennas such as frequency independent and broad band
TEXT BOOK:
1.
John D Kraus,” Antennas for all Applications”, 3 rd
Edition, Mc Graw Hill, 2005.
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PIT ECE VI SEM
REFERENCES:
1.
Edward C.Jordan and Keith G.Balmain” Electromagnetic Waves and Radiating Systems” Prentice
Hall of India, 2006
2.
R.E.Collin,”Antennas and Radiowave Propagation”, Mc Graw Hill 1985.
3.
Constantine.A.Balanis “Antenna Theory Analysis and Design”, Wiley Student Edition, 2006.
4. Rajeswari Chatterjee, “Antenna Theory and Practice” Revised Second Edition New Age
International Publishers, 2006.
5. S. Drabowitch, “Modern Antennas” Second Edition, Springer Publications, 2007.
6.
Robert S.Elliott “Antenna Theory and Design” Wiley Student Edition, 2006.
7. H.Sizun “Radio Wave Propagation for Telecommunication Applications”, First Indian Reprint,
Springer Publications, 2007.
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PIT ECE VI SEM
Course Name: Antenna and wave propagation (EC-6602)
Year of Study: 2016–2017 (R-2013)
On completion of course students will be able to
S. No.
Course outcome
1
CO1
Statement
Apply fundamental parameters related to antenna and basics of wire antennas.
2
CO2
Obtain information about basic theorem, design and analyse of aperture antenna
3
CO3 Apply antenna parameters, design and analyse antenna arrays.
4
CO4
Apply, analyse and the design equations of special antennas for the low and high frequency applications
5
CO5
Acquire knowledge of various types of radio wave propagation and basic parameter of radio waves
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PIT ECE VI SEM
UNIT 1
FUNDAMENTALS OF RADIATION
PART A
Definition of antenna parameters – Gain, Directivity, Effective aperture, Radiation
Resistance, Band width, Beam width, Input Impedance. Matching – Baluns, Polarization mismatch,
Antenna noise temperature, Radiation from oscillating dipole, Half wave dipole. Folded dipole,
Yagi array.
1.
Define Antenna. [ Remember ]
An antenna is a structure that has been designed to radiate or receive electromagnetic waves.
2.
Define an Isotropic Antenna. [ Remember ]
An Isotropic Antenna is the one which radiate energy uniformly in all directions.
3.
Define Radiation pattern. (NOV / DEC 2012) [ Remember ]
An antenna radiation pattern is defined as a mathematical function or a graphical representation of the radiation properties of the antenna as a function of space coordinates. The radiation properties include power flux density, radiation intensity, field strength, directivity, phase or polarization.
4.
What are the 2 types of radiation pattern? [ Understand ]
The 2 types of radiation pattern are ( a) Field pattern and (b) power pattern
Field pattern: If the radiation from the antenna is expressed in terms of the field strength (either E or H), then the radiation pattern is called as field pattern.
Power pattern: If the radiation pattern from the antenna is expressed in terms of power per unit area, then the resultant pattern is called power pattern.
5.
Define Radiation resistance of antenna .
(APRIL / MAY 2011) (MAY / JUNE 2016) [ Remember ]
Radiation resistance is defined as a ‘Virtual resistance that does not exist physically but is a quantity coupling the antenna to distant region s of space via a transmission line’.
6.
Define half power beam width. (NOV / DEC 2012) [ Remember ]
Half power beam width is defined as the angular width measured in the radiation pattern between points where the power is half of its maximum value. It is also called -3 dB beam width.
7.
Define Radiation intensity. [ Remember ]
The power radiated from an antenna per unit solid angle is called radiation intensity (U). Its unit is watts per steradian and it is independent of distance.
8.
Define Directivity of Antenna .
(APRIL / MAY 2011) (NOV. / DEC. 2011) [ Remember ]
Directivity is defined as the ratio of Radiation intensity of test antenna in a given direction to radiation intensity of isotropic antenna. D = U/U
0
Where U= Radiation intensity of test antenna
U
0
= Radiation intensity of Isotropic antenna’
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PIT ECE VI SEM
It is also expressed as D

4

U
P rad
9.
What is front to back ratio? [ Remember ]
Front to Back Ratio (FBR) is defined as the ratio of power radiated in the desired direction to the power radiated in the opposite direction ie. FBR = power radiated in desired direction/power radiated in opposite direction
10.
Define Antenna efficiency. [ Remember ]
Antenna Efficiency is defined as the ratio of power radiated to the total input power applied to the antenna.
Antenna efficiency, k = P rad
/P in
(dimensionless)
Where P rad
- Radiated power in watts
P in
- Input power in watts
11.
Define Reciprocity principle. [ Remember ]
Reciprocity principle is stated as follows,’ If an emf is applied to the terminals of antenna no. 1 and the current measured at the terminals of another antenna no. 2, then an equal current both in amplitude and phase will be obtained at the terminals of antenna no. 1 if the same emf is applied to the terminals of antenna no.2’
12.
What do you meant by Antenna aperture? [ Understand ]
Antenna aperture or equivalent areas are those which are used to describe the power capturing characteristics of the antenna when a wave impinges on it.
13.
Define Effective aperture . (NOV. / DEC. 2011) [ Remember ]
Effective aperture is defined as the ratio of power received at the antenna load terminal to the pointing vector (power density) of the incident wave. Its unit is W/m 2 .
14.
What is the relationship between effective aperture and directivity? [ Remember ]
The relationship between effective aperture and directivity is D= 4πA e
/λ 2
15.
Define antenna Gain. [ Remember ]
Gain is defined as the ability of the antenna to concentrate the radiated power in a given direction or absorb effectively the incident power from that direction.
16.
Define antenna beam-width.
Antenna beam-width is an angular width in degrees, measured on the major lobe of its radiation pattern between points where the radiated power has fallen to half of its maximum value. It is a measure of directivity of an antenna.
17.
Define antenna band-width. [ Remember ]
The bandwidth of an antenna is defined as the range of frequencies on either side of a center frequency where the antenna characteristics such as input impedance, beam-width, polarization, side lobe level, gain, beam direction, radiation efficiency, and radiation pattern are within an acceptable value of those at the center frequency.
18.
Define antenna input impedance. [ Remember ]
An antenna input impedance is nothing but the impedance offered by the input terminals of the antenna.
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PIT ECE VI SEM
19.
What is folded dipole[ Understand ]
In folded dipole antenna, two half wave dipoles have been folded and joined together in parallel at the ends.
20.
What is BALUN [ Remember ]
A balun is a device that connects a balanced line to an unbalanced line. It is used to balance an unbalanced system. For example, balun connects a twisted pair cable with a coaxial cable.
21.
What is polarization mismatch [ Remember ]
Generally, the polarization of the receiving antenna is not the same as the polarization of the incident wave; this is called as polarization mismatch.
22.
What is antenna noise temperature? [ Remember ]
The antenna noise temperature is defined as temperature of far field region of space and near surroundings which are coupled to the antenna through radiation resistance.
23. Define Hertzian dipole. [ Remember ]
Hertzian dipole is defined as a short linear conductor or short electric dipole whose length is very short compared to wave length (L<<λ) and current is assumed to be constant throughout its length l.
PART B
1.
Define the following parameters w.r.t antenna: [ Remember ] i.
Radiation resistance. ii.
Beam area. iii.
Radiation intensity. iv.
Directivity. v.
Gain. vi.
Isotropic radiator. vii.
Directive gain. viii.
Hertzian dipole. ix.
Power gain. x.
Efficiency. xi.
Power density. xii.
Steradians & radians.
2.
With the help of neat diagrams explain the principle of radiation in antennas.
[ Analyze ]
3.
Explain antenna as a transmitting device and as a receiving device.
[ Understand ]
4.
Write a note on radiation pattern and radiation lobes.
[ Remember ]
5.
Draw the radiation pattern of: (i) Directional antenna. (ii) Isotropic antenna. [ Apply ]
6.
Explain different types of aperture.
[ Understand ]
7.
Define aperture of an antenna and find its relation with directivity. [ Remember ]
8.
Explain effective height of an antenna.
[ Remember ]
9.
Derive FRIIS transmission formula and explain its significance. [ Apply ]
10.
Derive an expression for power radiated by an isotropic antenna.
[ Apply ]
11.
Derive the relation between directivity and beam solid angle.
[ Apply ]
12.
Derive the relationship between radiation resistance and efficiency.
[ Apply ]
13.
Derive an expression for field intensity at a distant point.
[ Apply ]
14.
Write short notes on: (a) Fields of an oscillating dipole [ Remember ]
(b) Antenna field zones.
15.
Show that an isotropic radiator radiating 1 KW power gives a field of 173mv/m at a distance of 1
Km.
[ Apply ]
16.
Find the directivity of an antenna having radiation resistance of 72 Ω and loss resistance of 12 Ω and a gain of 20. [ Understand ]
17.
What is the maximum effective aperture of a microwave antenna which has a directivity of 900?
[ Remember ]
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PIT ECE VI SEM
18.
Using FRISS transmission formula find the maximum power received at a distance of 0.75 Km over a free space. A 100 MHz circuit consisting of a transmitting antenna of 30dB gain and a receiving antenna with a 25dB gain is used. The power input to the transmitting antenna is 120W. [ Apply ]
19.
A radio station radiates a total power of 10KW and a gain of 30. Find the field intensity at a distance of 100Km from the antenna. Assume free space propagation.
[ Apply ]
20.
Find the number of square degrees in the solid angle on a spherical surface that is between θ=20 o and 40 o and Φ=30 o and 70 o .
[ Apply ]
21.
Calculate the length of half wave dipole antenna meant to have wavelength at 60MHz.
[ Apply ]
22.
Calculate the gain of an antenna with a circular aperture of diameter 3m at a frequency of 5 GHz.
[ Apply ]
23.
An antenna radiates a total power of 100W in the direction of maximum radiation, the field strength at a distance of 10Km was found to be 12mV/m. What is the gain of the antenna? Assume free space propagation. If η=90% find directivity. [ Apply ]
24.
An antenna has a radiation resistance of 72Ω loss resistance of 8ƒ Ω power gain of 12dB. Determine the antenna efficiency and directivity. [ Apply ]
25.
An antenna has a loss resistance of 10 Ω power gain of 20 and directivity gain of 22. Calculate the radiation resistance. [ Apply ]
26.
Calculate the effective length of a λ/2 antenna gives Rr=73 Ω effective aperture 0.13 m 2 .
[ Apply ]
27.
An antenna radiates power equally in all directions. The total power delivered to the radiator is 100
KW. Calculate the power density at distance of (i) 100m (ii) 1000m.
[ Apply ]
28.
Explain power theorem. [ Remember ]
29.
Find the directivity for the following intensity patterns: i.
Hemispheric power pattern of a uni directional antenna. ii.
Unidirectional cosine power pattern. iii.
Bi directional sine power pattern. iv.
Bi directional sin 2 power pattern. v.
Unidirectional cos 2 power pattern.
30.
Show that directivity for unidirectional operation is 2(n+1) for an intensity variation of U=UmCos
θ? [ Apply ] n
31.
Derive the electric and magnetic field components of Hertzian dipole. [ Apply ]
(APRIL / MAY 2011)
32.
Explain the following terms with respect to antenna, (APRIL / MAY 2011) [ Remember ] i). Polarization ii). Effective aperture iii). Directivity iv). Antenna temperature
v). Radiation pattern
33.
What are Hertzian dipoles? Derive the electric and magnetic field quantities of Infinitesimal dipole and radiation pattern . (NOV. / DEC. 2011) [ Remember ]
34.
Explain the following terms with respect to antenna, (NOV. / DEC. 2011) [ Remember ] i). Polarization ii). Beam solid angle iii). Gain iv). Bandwidth
v). Radiation pattern
35. Solve the wave equation for uniform plane waves in an infinitely extending conducting medium.
(MAY / JUNE 2012) [ Understand ]
36. Write short notes on: (MAY / JUNE 2012) [ Remember ] i). Radiation pattern ii). Polarization
iii). Antenna temperature.
37. Define and explain in detail the terms “Radiation Resistance”,”Gain”,”directivity”,”effective aperture” and ”polarization”.
(NOV / DEC 2012) [ Understand ]
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PIT ECE VI SEM
38. Derive the electric and magnetic field components of Hertzian dipole” (NOV / DEC 2012) [ Apply ]
39. i). Explain the principle of reciprocity as applied to an antenna. (MAY / JUNE 2013) [ Understand ] ii). Derive the wave equation and obtain its solution. [ Apply ]
40. i). What is the effective length of linear antenna?
(MAY / JUNE 2012) [ Understand ]
ii). Derive the expression for the radiated fields of a center fed λ/2 dipole antenna. Sketch the radiation pattern. [ Understand ]
41. Derive the expression for the field quantities radiated from a λ/2 diploe and prove that the radiation resistance to be 73Ω. (MAY / JUNE 2016) [ Aply ]
42. Derive the expression for the field quantities (E and H) for a small oscillation current element.
(MAY / JUNE 2016) [ Apply ]
43. Explain the principle of radiation from an oscillating electric dipole. Derive the near field and far field expressions (NOV / DEC 2016) [ Remember ]
44. Derive the expressions for the fields at a far point due to a half wave dipole (NOV / DEC 2016)
[ Apply ]
ASSIGNMENT QUESTIONS:
1.
Derive the solution for the wave equations and explain about the vector and scalar potential in detail
(PO2) [ Understand ]
2.
Give the practical example for the reciprocity theorem(PO1) [ Remember ]
3.
Explain the radiation mechanism of antenna in detail (PO1) [ Remember ]
4.
Explain the different types of antenna used for various communications(PO1) [ Remember ]
5.
Compare and analyse the different parameters of antenna(PO2) [ Analyze ]
6.
Draw the radiation pattern of different types of antennas.(PO1) [ Remember ]
7.
Draw and mention the effective aperture of the various antennas.(PO1) [ Remember ]
8.
What is an infinitesimal dipole and derive its radiated field components and power radiated
.(PO2)[ U nderstand ]
9.
Describe in detail about the half-wave dipole antenna and its properties. (PO1) [ Remember ]
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PIT ECE VI SEM
UNIT II
PART A
APERTURE AND SLOT ANTENNAS
Radiation from rectangular apertures, Uniform and Tapered aperture, Horn antenna , Reflector antenna , Aperture blockage , Feeding structures , Slot antennas ,Micro strip antennas – Radiation mechanism – Application ,Numerical tool for antenna analysis
1.
State Huygen’s principle or field equivalence principle. (APRIL / MAY 2011), (NOV / DEC
2012) [ Remember ]
Huygen;s principle states that ‘ each point on a primary wave front can be considered to be a new source of a secondary spherical wave and that a secondary wave front can be constructed as the envelope of these waves.
2.
State Uniqueness theorem : (MAY / JUNE 2012) [ Remember ]
The uniqueness theorem can be stated in several different forms but it essentially states that for a given set of sources and boundary conditions in a lossy medium, the solution to Maxwell's equations is unique.
3.
State field equivalence principle. [ Remember ]
According to the field equivalence principle, ‘the fields in V2 due to the sources in volume V
1 can also be generated by an equivalent set of virtual sources on surface S, given by J s = n x H and M, =
1
E x n, where E and H are the fields on the surface S produced by the original set of sources in volume V
’
4.
State Babinet’s principle .
(NOV. / DEC. 2011), (MAY / JUNE 2013) (MAY / JUNE 2016)
[ Remember ]
It states that ‘When the field behind a screen with an opening is added to the field of a complementary structure, the sum is equal to the field when there is no screen’.
5.
What is a slot antenna? (NOV / DEC 2012) [ Remember ]
The slot antenna is an opening cut in a sheet of conductor which is energized via a coaxial cable or waveguide.
6.
Which antenna is complementary to the slot antenna? [ Remember ]
The dipole antenna is complementary to the slot antenna. The metal and air regions of the slot are interchanged for the dipole.
7.
What is the relationship between the terminal impedances of slot and dipole antennas?
[ Remember ]
Z s
Z d
= η
0
2 /4
Where Z
S
= terminal impedance of slot antenna
Z d
= Terminal impedance if dipole antenna
η
0
= Intrinsic impedance of free space = 377 ohms
8.
What is the difference between slot antenna and its complementary antenna? [ Remember ] i.
Polarization are different ie. The electric fields associated with the slot antenna are identical with the magnetic field of the complementary dipole antenna. ii.
The electric field be vertically polarized for the slot and horizontally polarized for the dipole. iii.
Radiation from the back side of the conducting plane of the slot antenna has opposite polarity from that of complementary antenna.
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PIT ECE VI SEM
9.
What are the methods of feeding slot antenna? [ Remember ] i) Coaxial line feed ii) iii)
Waveguide feed
10.
Define Lens antenna. [ Remember ]
An antenna which collimates the incident divergent energy to prevent it from spreading in undesired direction is called as lens antenna.
11.
What are the different types of lens antenna? [ Remember ]
Lens antenna can be divided into 2 types. a.
Dielectric lens or H plane metal plate lens b.
E plane metal plate lens antenna. c.
12.
What is dielectric lens antenna? [ Remember ]
Dielectric lens antennas are the antennas in which the traveling wave fronts are delayed by lens media.
13.
Name the materials used for dielectric lens construction. [ Understand ]
Polystyrene and polyethylene are the important materials used for dielectric lens construction.
14.
Define E plane metal plate lens antenna. [ Understand ]
It is an antenna in which the traveling wave fronts are spaced by the lens medium.
15.
Define refractive index of lens antenna. [ Understand ]
It is defined as the ratio of velocity of wave in air to the velocity of wave in lens medium.
16.
What are the different methods of feeding slot antennas? [ Understand ]
Slot antenna can be a.
Waveguide fed slot b.
Boxed in slot c.
Coaxial transmission line d.
17.
17. What do you mean by sectoral horn? [ Understand ]
If flaring is done only in one direction, then its called as sectoral horn.
18. What do you mean by pyramidal horn antenns? (APRIL / MAY 2011)
If flaring is done only along both the walls, then its called as pyramidal horn.
19. What are the various feeds used in reflector? [ Understand ]
Dipole, horn, end fire, cassegrain feeds.
20. Define spill over. [ Remember]
Some of the desired rays are not captured by the reflector antenna and this constitute spill over.
21. What is back lobe radiation? [ Understand ]
Some radiation from the primary radiator occurs in the forward direction in addition to the desired parallel beam. This is known as back lobe radiation.
22. What are various feeds used in reflector? [ Understand ] a.
Dipole antenna b.
Horn feed c.
End fire feed d.
Cassegrain feed e.
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PIT ECE VI SEM
23.
What are the advantages of cassegrain feed antenna? [ Understand ]
1.
Reduction in spill over
2.
Simple in construction
3.
Quite inexpensive
4.
Widely used in fixed point to point microwave communication
5.
Satellite reception and tracking
6.
Ability to place feed in a convenient location
24.
What are the different types of horn antenna? (MAY / JUNE 2013) [ Understand ] f.
Sectoral horn g.
Pyramidal horn h.
Conical horn i.
Biconical horn antenna
25. What are the uses of horn antenna? [ Understand ]
Horn antenna are extensively used at microwave frequencies under the condition that power gain needed is moderate. For high power gain, since the horn dimensions become large, so the other antennas like lens or parabolic reflector etc. are preferred rather than horn.
26.
Why antenna measurements are usually done in Fraunhofer zone? (MAY / JUNE 2016)
[ Understand ]
The far-field patterns are measured on the surface of a sphere of constant radius. Any position on the sphere is identified by the directional angles θ and ϕ of the spherical coordinate system. In general, the pattern of an antenna is 3-D. However, 3-D pattern acquisition is difficult – it involves multiple 2-D pattern measurements. The minimal number of 2-D patterns is two, and these two patterns must be in two orthogonal principal planes. A principal plane must contain the direction of maximum radiation.
27.
The radiation resistance of an antenna is 72 Ω and loss resistance is 8Ω. What is the directivity (in dB), if the power gain is 15? (MAY / JUNE 2016) [ Apply ]
Directivity – 35.13
PART B
1.
What is Horn Antenna? Sketch the various types of Horn Antenna and explain its operation.
[ Understand ]
2.
Describe the principle of operation and applications of parabolic reflectors and derive its necessary equations.
[ Analyze ]
3.
Explain Slot antenna and derive its field expressions.
[ Understand ]
4.
Explain the methods of feeding Slot Antenna? [ Understand ]
5.
Explain the different types of Lens antenna and derive their equations. [ Understand ]
6.
Describe Flat sheet and corner reflectors and derive their field equations. [ Understand ]
7.
Explain the following theorem in detail [ Understand ] i.
Uniqueness theorem ii.
Field equivalence principle iii.
Method of images iv.
Huygenes principle v.
Babinets principle vi.
Duality principle
8.
Explain the structure and operation of Slot antenna. Also derive the expression of its input impedance.
[ Understand ]
9.
Explain the working operation of parabolic reflector antenna in detail. [ Understand ]
10.
Explain the working operation of lens antenna. Also explain its types.
[ Understand ]
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PIT ECE VI SEM
11.
Explain the operation of hyperbolic reflectors and derive its equation.
[ Understand ]
12. Explain the radiation mechanism of microwave Horn antenna with diagram.
(NOV. / DEC. 2011) [ Understand ]
13. Explain the special features of parabolic reflector antenna and discuss on different types of feed used with neat diagram.
(NOV. / DEC. 2011) [ Understand ]
14. Explain the radiation mechanism of slot antenna with diagram.
[ Understand ]
(APRIL / MAY 2011)
15. Explain the special features of reflector antenna and discuss on different types of feed used with neat diagram.
(APRIL / MAY 2011) [ Understand ]
16. With field equivalence principle explain radiation mechanism
(MAY / JUNE 2012) [ Understand ]
17. Describe the working of slot antenna. What is the terminal impedance of slot antenna (MAY / JUNE
2012?) [ Apply ]
18. What is reflector antenna? With necessary diagrams, explain parabolic reflector antenna and its different types of feeding systems.
(MAY / JUNE 2012) [ Remember ]
19. How is aperture blockage in reflector antennas avoided?
(MAY / JUNE 2012) [ Understand ]
20. Explain the principles of rectangular horn with a neat sketch. Draw various types of horn structure.
(NOV. / DEC. 2012) [ Understand ]
21. With neat diagram, explain the principle of parabolic reflector antenna and various types of feed used.
(NOV. / DEC. 2012) [ Understand ]
22. i). Compare flat reflector and corner reflector antennas.
(MAY / JUNE 2013) [ Understand ]
ii). Explain how a paraboloidal antenna gives a highly directional pattern.
iii). Explain in detail about the feeding structure of parabolic reflector antenna.
23. Write short notes on. (MAY / JUNE 2013) [ Remember ] i). Slot antenna. ii). Lens antenna.
24.
Discuss the geometry of a parabolic reflector and the significance of f/D ratio. Explain its feed configuration.
(MAY / JUNE 2016) [ Understand ]
25.
Discuss the construction and design of a Yagi-uda array. Show that the impedance of a folded dipole is 300Ω.
(MAY / JUNE 2016) [ Understand ]
26.
Explain in detail the radiation from a slot antenna and their feed systems (NOV. / DEC. 2016)
[ Understand ]
27.
Explain the radiation mechanism of reflector antennas and their feed systems (NOV. / DEC. 2016)
[ Understand ]
ASSIGNMENT QUESTIONS:
1.
Write and explain the field equivalence principle in detail (PO1) [ Remember ]
2.
State and explain the Love’s equivalence principle & electric and magnetic conductor equivalence principle (PO2) [ Understand ]
3.
Derive the equations of the computations of field quantities of aperture antenna.(PO2)
[ Understand ]
4.
Mention the relation between the wire and aperture antennas.(PO2) [ Understand ]
5.
Derive the result from Booker's principle (PO2) [ Understand ]
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PIT ECE VI SEM
6.
Explain the horn antenna design principle in detail.(PO1) [ Remember ]
7.
Design and draw the reflector antenna and mention its applications .(PO3) [ Create ]
8.
Design a parabolic dish reflector with the diameter of the dish D equal to 11 wavelengths.
The F/D ratio will be 0.5. (PO3)[ Create ]
Answer: The maximum antenna gain from the physical aperture is actual gain is 29.3 dB = 851, so we can conclude that the overall efficiency is 77%.
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PIT ECE VI SEM
UNIT III
ANTENNA ARRAYS
PART A
N element linear array, Pattern multiplication, Broadside and End fire array – Concept of
Phased arrays, Adaptive array, Basic principle of antenna Synthesis-Binomial array
1.
Define antenna array. [ Remember ]
A radiating system composed of several spaced and properly phased radiators is called as an array.
2.
Define linear array. [ Understand ]
An antenna array is said to be linear if the individual antennas of the array are equally spaced along a straight line.
3.
Define uniform linear array. [ Understand ]
An uniform linear array is one in which the elements are fed with a current of equal magnitude with uniform phase shift along a line.
4.
Define Broadside array. [ Understand ]
Broadside array is defined as an arrangement in which the principal direction of radiation is perpendicular to the array axis and also to the plane containing the array element. The phase difference between adjacent elements is zero.
5.
Define end fire array. (NOV / DEC 2012) [ Understand ]
End fire array is defined as an arrangement in which the principal direction of radiation coincides with array axis.
6.
What is array factor? [ Remember ]
The factor by which the array increases the field strength over that of a single element radiation the same total power is array factor.
7.
Define the principle of pattern multiplication .
(NOV. / DEC. 2011), (APRIL / MAY 2011), (NOV /
DEC 2012), (MAY / JUNE 2013) [ Remember ]
The principle of pattern multiplication states that, ‘The total field pattern of an array of nonisotropic but similar point sources is the multiplication of the individual source patterns and the pattern of an array of isotropic point sources, each located at the phase centre of individual source and having the same relative amplitude and phase while the total phase pattern is the addition of the phase pattern of the individual sources and the array of isotropic point sources’.
8.
What is the advantage of pattern multiplication? [ Understand ]
The principle of pattern multiplication provides a speedy method for sketching the radiation pattern of complicated arrays just by inspection.
9.
What is uniform amplitude distribution? [ Understand ]
If the sources are in phase and all equal in amplitude, then it is called uniform amplitude distribution.
10.
Define phased array. [ Understand ]
Phased array is an array of many elements with the phase of each element being a variable, providing control of the beam direction and pattern shape.
11.
Define adaptive array. [ Remember ]
Adaptive array use signal processing algorithms to adapt to user movement, changes in the radiofrequency environment and co-channel interference.
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PIT ECE VI SEM
12.
What is a retro array? [ Understand ]
If a wave incident on an array is received and transmitted back in the same direction, the array acts as a retro-array.
13.
What is binomial array? [ Understand ]
To reduce the side lobe level, John Stone proposed that sources have amplitudes proportional to the coefficients of a binomial series of the form,
(𝑎 + 𝑏) 𝑛−1
= 𝑎 𝑛−1
+ (𝑛 − 1)𝑎 𝑛−2 𝑏 +
(𝑛 − 1)(𝑛 − 2)
2!
𝑎 𝑛−2 𝑏
2
+ ⋯
14.
Define gain of the antenna and bring out the relationship between gain and aperture of an antenna. [ Remember ]
Gain is defined as the ability of the antenna to concentrate the radiated power in a given direction or absorb effectively the incident power from that direction.
PART B
1.
Write a note on antenna arrays. Mention the factors on which the resultant pattern of array depends. [ Remember ]
2.
Differentiate between BSA and EFA. [ Apply ]
3.
Draw the radiation pattern of [ Apply ] i.
2 isotropic point sources of same amplitude and phase that are λ/2 apart along X axis symmetric w.r.t origin ii.
2 isotropic point sources of same amplitude and phase that are λ/2 apart along X axis symmetric w.r.t origin iii.
2 isotropic point sources of same amplitude and opposite phase that are λ/2 apart along X axis symmetric w.r.t origin iv.
2 isotropic point sources of same amplitude and phase that are λ/2 apart along X axis with 1 source at origin v.
2 isotropic point sources of same amplitude and in phase quadrature.
4.
Derive an expression for electric field intensity of array of n isotropic sources of equal amplitude and spacing and having a phase difference of 90

. [ Apply ]
5.
Explain the principle of pattern multiplication. [ Understand ]
6.
Obtain the electric field intensity of non isotropic but similar point sources.
7.
Obtain the radiation pattern of 4 sources forming a uniform BSA with a spacing of λ/2.
[ Apply ]
8.
4 sources have equal magnitude & are spaced λ/2 apart. Maximum field is to be in line with sources. Plot the field pattern of the array [ Apply ]
9.
Find BWFN for uniform EFA & extended EFA. Given (i) n=4 (ii) d= λ/2. [ Apply ]
10.
The principle lobe width of uniform 10 elements of BSA was observed to be 30 o
at a frequency of 30MHz. Estimate the distance between the individual elements of the array.
[ Apply ]
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PIT ECE VI SEM
11.
Calculate the efficiency of an antenna operated at 500 KHz and having a resistance 12 Ω and effective height=30m. [ Apply ]
12.
2m long vertical wire carries a current of 5A at 1MHz find the strength of the radiated field at 30Km in the direction at right angles to the axis of the wire. Assume that the wire is in free space. [ Apply ]
13.
A plain wave is incident on a short dipole. The wave is linearly polarized with electric field in the Y-direction. The current on the dipole is assumed constant and in the same phase over entire length. The antenna loss resistance=0. Find the dipole maximum effective aperture and directivity. [ Apply ]
14.
Write a note on loop antenna. [ Remember ]
15.
Derive electric and magnetic fields of a loop antenna. [ Apply ]
16.
Compare far fields of small loop and short dipole. [ Apply ]
17.
Derive an expression for radiation resistance of a loop antenna. [ Apply ]
18.
a)Obtain the Maxima, Minima and half power directions of radiated field of 2 identical isotropic point sources spaced ‘d’ apart and i) Fed with current of equal magnitude and same phase ii) fed with current of equal magnitude and opposite phase. [ Apply ]
19.
b) Find the direction of pattern maxima, pattern minima for an array of n sources with equal amplitude and spacing in broadside case. [ Apply ] ii) Explain array of non-uniform excitation with neat diagrams.
20.
a) i)Explain the principle of pattern multiplication with neat diagrams.
ii) Design a 4 element, broadside array of isotropic elements spaced λ/2 apart that has an array factor with all the side lobes 25 dB below the main lobe
21. Derive the near field and far field electric and magnetic components of finite length dipole and obtain the radiation pattern for various values of the length. (NOV. / DEC. 2012) [ Apply ]
22. For a 2 element linear antenna array separated by a distance d=3 λ/4, derive the field quantities and draw its radiation pattern for the phase difference of 45˚.
(NOV. / DEC. 2012)
[ Apply ]
23. i). What is binomial array (MAY / JUNE 2013) [ Understand ] ii). Draw the pattern of 10 element binomial array with spacing between the elements of 3
λ/4 and λ/2.
24.
Derive the expressions for field pattern of broad side array of n point sources.
(MAY /
JUNE 2013) [ Apply ]
25.
Obtain the expression for the field and the radiation pattern produced by a N element array of infinitesimal with distance of separation λ/2 and currents of unequal magnitude and phase shift 180 degree (MAY / JUNE 2016) [ Apply ]
26.
i). Using pattern multiplication determine the radiation pattern for 8 element array, separated by the distance λ/2. ii). Write short notes on tapered array and phased array (MAY / JUNE 2016) [ Apply ]
27.
Derive and plot the radiation from a broadside array of 4 point sources. (NOV. / DEC.
2016) [ Apply ]
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PIT ECE VI SEM
28.
(i) Discuss in detail the concept, design ' principles and types of phased array.
(ii)What is the significance of binomial array? (NOV. / DEC. 2016) [ Apply ]
ASSIGNMENT QUESTIONS:
1.
Explain in detail about the N-element array with proper example .(PO1) [ Remember ]
2.
Obtain the pattern of two isotropic point sources with identical amplitude and phase currents, and spaced one-half wavelength apart. (PO3) [ Create ]
3.
An array consists of two horizontal dipoles located along z-axis at one-half wavelength apart. If the excitation magnitudes and phases are same, then obtain the shape of the radiation pattern (PO3)
[ Create ]
4.
Obtain the pattern of two isotropic point sources with identical amplitude and in phase quadrate currents, and spaced (i) one-half wavelength, (ii) quarter wavelength apart.(PO3) [ Create ]
5.
Explain in detail about the Adaptive array. (PO1) [ Remember ]
6.
Explain the concept of the pattern multiplication with examples. .(PO1) [ Remember ]
7.
What are the phased arrays and binomial arrays. .(PO2) [ Understand ]
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PIT ECE VI SEM
UNIT IV
SPECIAL ANTENNAS
Principle of frequency independent antennas –Spiral antenna, Helical antenna, Log periodic.
Modern antennas- Reconfigurable antenna, Active antenna, Dielectric antennas, Electronic band gap structure and applications, Antenna Measurements-Test Ranges, Measurement of Gain,
Radiation pattern, Polarization, VSWR
1.
What are the uses of helical antenna? [ Remember ] i.
Single or an array of helical antenna is used to receive or transmit the VHF signals through
Ionosphere. Helical antenna is, thus, frequently used for satellite and space probe communications. It has particular applications in space telemetry at the ground end of the telemetry link with ballistic missiles, satellites etc. at HF and VHF bands. The circular polarization is useful in these applications as polarization rotations of waves are produced by the Ionosphere (Faraday Effect).
ii.
The wide bandwidth, simplicity, highest directivity and circular polarization of the helical beam antenna have made it indispensable for space communication applications.
For, it has been used in transmitting telemetry data from moon to earth] remains.
iii.
The dimensions of the helix in axial mode are not critical and thereby resulting in greater bandwidth. This end fire axial mode is more practical as it can achieve circular polarization over a wider bandwidth (normally 2:1) and it is more efficient. Because of circular polarization, helical antenna is capable of receiving signals of arbitrary polarization.
27.
What do you meant by parasitic elements?
[ Remember ]
The passive elements which are not connected directly to the transmission line but are electrically coupled are called as parasitic elements.
28.
What do you meant by driven elements?
[ Remember ]
Driven element is an active element where the power from the transmission line is fed or which feeds received power to the receiver.
29.
What is beam antenna?
[ Remember ]
If three elements array i.e. 1 reflector, 1 driven element and 1 director are used, then such type of yagi-uda antenna is called beam antenna.
30.
What is frequency independent antenna?
[ Remember ]
An antenna in which the impedance, radiation pattern and directivity remain constant as a function of frequency is called as frequency independent antenna. Eg. Log periodic Antenna.
31.
Why log periodic antenna is named so far?
[ Understand ]
The geometry of log periodic antenna is so chosen that electrical properties must repeat periodically with logarithm of the frequency.
32.
What is LPDA? (NOV. / DEC. 2011) [ Remember ]
LPDA means Log Periodic Dipole Array. It is defined as an antenna whose electrical properties repeat
19

PIT ECE VI SEM periodically with logarithm of the frequency.
33.
What are the 3 different regions in log periodic antenna and how they are differentiated?
[ Remember ] i.
Inactive region – L<λ/2 ii.
Active region – L= λ/2 iii.
Inactive reflective region –L>λ/2
34.
What are the applications of log periodic antenna?
[ Remember ] i.
ii.
iii.
HF Communication
Television reception
All round monitoring
35.
Define Rhombic Antenna.
[ Remember ]
An antenna which consists of 4 straight wires, arranged in the shape of a diamond, suspended horizontally above the surface of the earth is called Rhombic antenna. It is otherwise called diamond antenna or traveling wave antenna.
36.
What are the 2 types of rhombic antenna design?
[ Remember ] i.
Alignment design ii.
Maximum field intensity or maximum output design.
37.
What are the advantages of rhombic antenna?
[ Remember ]
An end to end receiving array of a number of rhombic can be designed to form a Multiple
Unit Steerable Antenna (MUSA) system which constitute the present day ultimate for long i.
distance short wave reception of horizontally polarized down coming waves.
The greatest advantage of the rhombic antenna is that the input impedance and radiation pattern do not change rapidly over a considerable frequency range as compared to any other system say of resonant dipoles. It is for this reason that rhombic antenna or its arrays have displaced broadside arrays for a number of services. ii.
It is a highly directional broad band antenna with greatest radiated or received power along the main axis or longer diagonal. iii.
It is very efficient. iv.
It is widely employed antenna for radio communication where enough space necessary for its installation is no problem. v.
It is simple and cheap to erect. vi.
Its input impedance is twice to that obtainable from a single side radiator. vii.
Vertical angle of radiation is low and hence these are suitable for long distance F – layer propagation. viii.
Short wave antennas of this kind require only a low height. ix.
Rhombic antennas are untuned and are a useful wideband antenna suitable for a rapid switching from one working frequency to another frequency.
38.
What are the limitations of rhombic antenna? [ Remember ] i.
It needs large space for installation.
Due to minor lobes, transmission efficiency is low. ii.
20

PIT ECE VI SEM
39.
What are the applications of rhombic antenna? [ Remember ] i.
HF transmission and reception ii.
Point to point communication
40.
What do you meant by self-impedance? [ Remember ]
Self-impedance is defined as the ratio of voltage to current at a pair of terminals.
Z
11
=R
11
+jX
11
Where, R
11
= Radiation resistance, X
11
= Self reactance
41.
What is mutual impedance? [ Remember ]
It is defined as the negative ratio of emf induced in one antenna to the current flowing in the antenna.
Mutual Impedance, Z
21
=-V
21
/I
1
(or) Z
12
=-V
12
/I
2
42.
What is the need for transposing the lines? [ Remember ]
In log periodic antenna, it is necessary to introduce 180˚ phase reversal between elements. This is accomplished by using a twisted transmission line (transposed line). In order to get 180 phase reversal between dipoles, the transmission line is trans-positioned.
43.
What is the effect of decreasing α? [ Remember ]
The directivity of an antenna increases by means of decreasing the induced angle α.
44.
What are the uses of LPDA? [ Remember ] i.
Like Rhombic the uses of Log periodic antennas lie mainly in the field of HF communication where multi band steerable (rotatable) and fixed antennas are generally used. However it has advantage that no power is wasted in terminating resistance. ii.
LPDA is also used for TV reception where only one log periodic design will suffice for all the channels even up to UHF band. iii.
It is best suited for all round monitoring in which case a single log periodic antenna will cover all the higher frequencies bands. If the cost in the installation is no problem.
45.
Define a traveling wave antenna. [ Remember ]
Traveling wave or non-resonant antennas are those antennas in which there is no reflected wave ie.
Only incident wave travel in the antenna.
46.
What is the type of radiation pattern produced when a wave travels in a wire? [ Remember ]
Unidirectional radiation pattern is produced when a wave travels in a wire.
47.
What is beverage or wave antenna? [ Remember ]
A single wire antenna terminated in its characteristic impedance may have essentially a uniform traveling wave. This type of antenna is referred to as beverage antenna.
48.
What is biconical antenna? [ Remember ]
The biconical antenna is a double cone antenna which is driven by potential, charge or an alternating magnetic field at the vertex. In this antenna, both the cones face in opposite direction.
49.
How spherical wave are generated? [ Understand ]
When a voltage V is applied at the input terminals of a biconical antenna, it will produce outgoing spherical waves. The biconical antenna acts as a guide for the spherical waves.
50.
What is turnstile antenna? [ Remember ]
It is an antenna composed of two dipole antennas perpendicular to each other. They intersect at their mid
21

PIT ECE VI SEM points. The current on the 2 dipoles are equal & in phase quadrature.
51.
What are the salient features of Turnstile antenna? [ Remember ] i.
Turnstile antenna consists of 2 half wave dipoles which are perpendicular to each other. The dipoles are excited with a phase difference of 90 0 with equal currents. ii.
The excitation is provided by non-resonant lines of unequal length. iii.
It produces almost an omni-directional pattern. iv.
Directivity is improved by the array of turnstile antennas. v.
It is best suited to match 70 ohm dual coaxial line. vi.
It is often used for TV & FM broadcasting in VHF&UHF bands vii.
It produces horizontal polarization. viii.
The polarization is disturbed due to loss of power. However, the purity of polarization is improved by super turnstile antennas. ix.
The super turnstile antenna can be made of 4 flat sheets x.
It is possible to obtain voltage standing wave ratio (VSWR) of about 1.1 over 30% bandwidth. xi.
It is used as a mast mounted TV transmitting antenna for frequencies about 50 MHz. xii.
Bandwidth is improved by an array of super turnstile antennas with a spacing of λ between the elements. xiii.
Array of super turnstile antennas produces more horizontal gain
52.
What do you meant by spiral antenna? [ Remember ]
Spiral is a geometrical shape found in nature. A spiral can be geometrically described using polar coordinates. Let (r,θ) be a point in the polar coordinate system. The equation r
 r
0 e a

------------- (1) where, r o and a are positive constants, describes a curve known as a logarithmic spiral or an equiangular spiral.
53.
What are Microstrip patch antennas? (APRIL / MAY 2011) [ Remember ]
Microstrip antennas are popular for low profile applications at frequencies above 100 MHz. they usually consists of a rectangular metal patch on a dielectric coated ground plane (circuit board). Hence, a microstrip patch antenna is also called as printed antenna.
54.
What are the advantages of Microstrip patch antenna? (NOV. / DEC. 2011) [ Remember ] i.
These antennas can be flush mounted to metal or other existing surfaces ii.
They only require space for the feed line which is normally placed behind the ground plane.
55.
What are the disadvantages of Microstrip patch antenna? [ Remember ] i.
Inefficiency ii.
Very narrow frequency bandwidth
56.
What are the methods of feeding microstrip antennas? [ Remember ]
A microstrip patch can be fed either by a microstrip transmission line [Fig. 6.55(a)J or by a coaxial transmission line [Fig. 6.55(b). The microstrip line can be etched along with the patch in a single process. In order to access the appropriate impedance point on the patch, a recess is created in the patch.
The depth of the recess is adjusted to achieve the impedance matching. A coaxial transmission line is attached right below the patch, with the inner conductor soldered to the patch and the outer conductor of the coaxial line connected to the ground plane. A patch antenna fed by either a microstrip or a coaxial transmission line has about 2 to 4% input bandwidth.
22

PIT ECE VI SEM
57.
What do you meant by biconical antenna?
[ Remember ]
A biconical antenna consists of 2 infinitely large (L
 
) cone arranged such that there axes are in line and the vertices are an infinitesimal distance away from each other.
The 2 cones are fed by a balanced transmission line connected to their vertices. It can be shown that the transmission line formed by the 2 infinite cones. Has characteristic impedance which is only a function of the cone angle but independent of the radial distance from the feed point.
58.
What is planar inverted F antenna? [ Remember ]
It is seen that the electric field along the centre line of a rectangular half wavelength long microstrip patch antenna is zero. Therefore, we can introduce a perfect electric conductor along this line between the patch and the ground plane without disturbing the fields of the patch, resulting in a quarter wavelength long antenna. This structure is known as a planar inverted F antenna (PIFA).
59.
List the different ranges of antenna measurements.
[ Remember ]
The following ranges are used for antenna parameter measurements.
1. TEM cell 2. GTEM cell 3. Outdoor range 4. Indoor range 5.Reflection range
6. Slant range 7. Elevated range 8.Compact range
10. Near field range 11. Ground range
9. Anechoic chamber
12. Radar cross section range
60.
What is reflection range? [ Remember ]
In an elevated range, the goal is to minimize the reflected signal from the ground. In a reflection range, the signal reflected off the ground is used to create constructive interference and hence a uniform wave front in the region of the antenna under test. This can be achieved by careful design of the reflecting surface. Hence the design of a reflection range is more complicated than that of an elevated range. Ground reflection ranges are very useful in the VHF band of frequencies for measuring moderately broad patterns.
61.
Define slant range. [ Remember ]
In a slant range, the transmit antenna is kept very close to the ground and the test antenna along with its positioner is mounted on a non-conducting tower
62.
What is anechoic chamber?
[ Remember ]
A closed chamber can be made reflection-free or echo-free by lining all the surfaces of the chamber with absorbing material. Such a chamber is known as an anechoic chamber.
63.
What are the differences between indoor and outdoor range?
[ Remember ]
S.No. Indoor range
1. These are protected from external Emi
Outdoor range
These are susceptible to Emi
2.
3.
4.
Space is limited
Only small antennas can be tested
Space is unlimited
Antennas of any size can be tested
Ground and other reflections are controlled Ground and other reflections cannot be controlled fully.
They have controlled environment They have uncontrolled environment 5.
6. They have all weather capability They do not have all weather capability.
64.
What are the various factors in which the selection of various ranges depend on? [ Remember ] i.
Frequency ii.
Cost iii.
Accuracy required iv. Size of the antenna and so on.
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PIT ECE VI SEM
65.
Mention the techniques for measuring gain of antenna? [ Remember ] i. Absolute gain measurement ii.
Gain transfer method
66.
What are secondary antennas? Give examples.
[ Understand ]
Antennas that are not radiators by themselves are called as secondary antennas.
Eg. Cassegrain, Hyperbolic.
67.
State Rumsey principle on frequency independence .
(MAY / JUNE 2016)
[ Remember ]
It states that, Impedance and pattern property of an antenna will be frequency independent if the antenna shape is specified in terms of angles.
PART B
1.
With neat sketch, explain the construction and operation of Helical antenna. [ Apply ]
(APRIL / MAY 2011)
2.
With neat sketch, explain the construction and operation of MultielementYagi-Uda antenna.
[ Apply ] (NOV. / DEC. 2011) .
3.
With necessary illustrations explain the radiation characteristics of microstrip antenna and mention its possible applications. [ Apply ] (NOV. / DEC. 2011) .
4.
With suitable geometry describe the design of a log periodic dipole array.
[ Apply ]
(MAY / JUNE 2012)
(MAY / JUNE 2012) i). Directivity measurement
5.
Explain in detail about:[ Apply ] ii). Gain measurement
6.
With necessary illustration explain the radiation characteristics of multi element log periodic antenna and mention its possible applications.
[ Apply ](NOV. / DEC. 2012) .
7.
Draw and explain the function of Helical antenna and various modes of radiation. Highlight some of its applications.
[ Apply ] (NOV. / DEC. 2012) .
8.
With neat diagram explain helical antenna and brief describe its operation in the axial mode.How does it differ from other antennas?
[ Apply ] (MAY / JUNE 2013)
9.
With neat block diagram explain how radiation pattern and gain of an antenna can be measured. [ Apply ] (MAY / JUNE 2013)
10.
i). Differentiate V antenna from Rhombic antenna and explain their construction and principles in detail. [ Apply ] (NOV. / DEC. 2013) . ii). Explain the design details of log periodic dipole antenna.
11.
i). Draw a neat block diagram for antenna radiation pattern measurement. Explain the procedure in detail.
[ Apply ] (NOV. / DEC. 2013) . ii). Give an account of “Helical Antenna”.
12. i). Explain the measurement of antenna gain. (MAY / JUNE 2014) ii). With necessary illustrations explain the radiation characteristics of YagiUda antenna.
13.With suitable diagrams the construction and principle of helical antenna in different mode of operation.
[ Apply ] (MAY / JUNE 2014)
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PIT ECE VI SEM
12.
i). Explain the design procedure for the construction of log periodic antenna ii). Discuss the construction equation for the helical antenna. (MAY / JUNE 2016) [ Apply ]
13.
Explain the measurement procedure for the measurement of VSWR and radiation pattern.
(MAY / JUNE 2016) [ Apply ]
14.
(i) Explain the operation and design of a helical Antenna. (NOV. / DEC. 2016) .
[ Apply ]
(ii) Explain the procedures involved in the measurement of gain in antennas.
(NOV. / DEC. 2016) . [ Apply ]
15.
Explain in detail about log periodic antennas. What is the need for feeding from end with shorter dipoles and the need for transposing the lines? Also discuss the effects of decreasing a. (NOV. / DEC. 2016) . [ Apply ]
ASSIGNMENT QUESTIONS:
1.
What is broad band antennas and explain the difference between the frequency dependent and independent antennas in detail.(PO1) [ Remember ]
2.
Give the examples and design equations of the frequency independent antennas.(PO2)
[ Understand ]
3.
Derive the design equations and explain the operations of the log periodic antennas. (PO2)
[ Understand ]
4.
Design a log periodic dipole array with 7dBi gain and a 4 to 1 bandwidth. Specify apex angle, scale constant k and number of elements. (PO3) [ Create ]
5.
What are the requirements of antenna measurements? .(PO1) [ Remember ]
6.
What is SAR in mobile and how it’s being measured in the antenna, explain in detail and how its going to be lowered.(PO2) [ Understand ]
7.
How the phase and polarization of an antenna is measured with neat setup(PO2)
[ Understand ]
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PIT ECE VI SEM
UNIT V
RADIO WAVE PROPAGATION
Modes of propagation , Structure of atmosphere , Ground wave propagation , Tropospheric propagation , Duct propagation, Troposcatter propagation , Flat earth and Curved earth concept
Sky wave propagation – Virtual height, critical frequency , Maximum usable frequency – Skip distance, Fading , Multi hop propagation
1.
What are the 3 modes of radio wave propagation? [ Remember ]
1.
Ground wave or surface wave propagation (upto 2 MHz)
2.
Sky wave or ionospheric wave propagation (Between 2 to 30 MHz)
3.
Space wave propagation (Above 30MHz)
2.
Define ground wave. [ Remember ]
A wave that is guided along the surface of the earth is called as ground wave or surface wave.
3.
What are the factors that cause attenuation in ground wave? [ Remember ]
Frequency, surface irregularities, permittivity, conductivity, diffraction and tilt in the wave front are the various factors that cause attenuation in ground wave.
4.
What are the 2 components present in space wave? [ Remember ]
1.
Direct wave – It reaches directly from transmitting antenna to receiving antenna.
2.
Indirect wave – It reaches receiving antenna after reflection from ground.
5.
Define Troposphere . [ Remember ]
The portion of the atmosphere which extends up to 16 Km from the earth surface is called Troposphere.
6.
Define LOS distance. [ Remember ]
Line Of Sight distance is a distance in which both the transmitting and receiving antenna can usually see each other.
7.
Define Ionosphere. [ Remember ]
The upper part of the atmosphere where the ionization is possible is known as Ionosphere.
8.
What are the different layers in Ionosphere? [ Remember ]
D layer, E layer, F
1
layer and F
2
layer are the layers in Ionosphere.
9.
Define fading. (MAY / JUNE 2013)
It is the fluctuation in the received signal strength at the receiver or a random variation in the received signal.
10.
How can we minimize fading? [ Remember ]
The most common method to minimize fading is diversity reception. In this method, some part of the signal is duplicated and even if one part experiences a deep fade, the other may not
11.
What are the various types of diversity reception? [ Remember ]
1.
Time diversity reception
2.
Frequency diversity reception
3.
Space diversity reception
12.
What do you meant by magneto Ionic splitting? [ Remember ]
The earth’s magnetic field splits up the incident waves into 2 different components. They are Ordinary wave and extra ordinary wave. This phenomenon of splitting of wave into 2 different components is called as magneto ionic splitting.
26

PIT ECE VI SEM
13.
Define Gyro frequency.
[ Remember ]
Gyro frequency f g
is defined as the frequency whose period is equal to the period of revolution of an electron in its circular orbit under the influence of earth’s magnetic flux B.
F g
= B e
/2πm
14.
Define critical frequency .
(NOV. / DEC. 2011) . [ Remember ]
The critical frequency f c
of an ionized layer is defined as the highest frequency which can be reflected by a particular layer at vertical incidence. It is different for different layer.
F c
= 9√N m
MHz
Where N m
= Maximum electron density in the layer.
15.
What is virtual height? (MAY / JUNE 2012) [ Remember ]
Virtual height is defined as the height to which a short pulse of energy sent vertically upward and traveling with the speed of light would reach taking the same 2 ways travel time as does the actual pulse reflected from the layer.
16.
Define MUF .
(APRIL / MAY 2011) [ Remember ]
Maximum Usable Frequency MUF is defined as the frequency which can be reflected back to earth for some specific angle of incidence.
F muf
= f c
sec i
Where f c
= critical frequency; i = angle of incidence
17.
State secant law. [ Remember ]
Secant law states that the maximum usable frequency is equal to the product of critical frequency and secant of incident angle.’
F muf
= f c
sec i
18.
Define space wave. [ Remember ]
Space wave is a wave that reaches the receiver either directly or after reflection from ground in the earth’s tropospheric region.
19.
Which layer of ionosphere is otherwise called as Kennelly haeaviside layer?
[ Remember ]
E layer
20.
How F layer has formed?
[ Understand ]
During night F
1
and F
2
layers combine and form one layer called F layer.
21.
Write down the expression for refractive index. [ Remember ]
Refractive Index,
 
1

81 N f
2
Where, N= Number of electrons per cubic meter f = frequency in Hz
22.
What are the factors that affect the propagation of radio waves? [ Remember ]
The factors that affect the propagation of radio waves are
1.
Earth’s magnetic field
2.
Frequency of the signal
3.
Curvature of earth
4.
Permittivity and conductivity
23. Define Maximum Usable Frequency (APRIL / MAY 2011) [ Remember ]
MUF is defined as the frequency which can be reflected back to earth for some specific angle of incidence.
PART B
1.
Write short notes on: [ Remember ] i.
Surface wave tilting. ii.
Space wave propagation. iii.
Ionosphere propagation. iv.
Structure of ionosphere.
27

PIT ECE VI SEM v.
Sky wave propagation. vi.
Duct propagation.
2.
Obtain an expression for space wave field component taking into account a direct wave field component and a reflected wave from the earth surface. [ Understand ]
3.
Derive an expression for refractive index of ionosphere. [ Apply ]
4.
Explain the following and derive the relevant expressions: [ Remember ] i.
Critical frequency. ii.
Maximum usable frequency. iii.
Virtual height. iv.
Skip distance.
5.
Briefly explain characteristics of different ionized layers in ionospheric propagation.
[ Understand ]
6.
Calculate the critical frequency for a medium at which the wave reflects if the maximum electron density is 1.24 X 10
6
electrons/cm
3
. [ Apply ]
7.
Which propagation will aid the following frequencies and why. (a) 120KHz. (b) 10MHz.
(c) 300 MHz. (d) 30GHz. [ Remember ]
8.
Estimate the surface wave tilt in degrees over an earth of 12mm conductivity and relative permittivity 20 at a wave length of 300m. [ Understand ]
9.
A transmitter radiates 100Wof power at a frequency of 50MHz, so that space wave propagation takes place. The transmitting antenna has a gain of 5 and its height is 50m. The receiving antenna height is 2m. It is estimated that field strength of 100 V/m is required to give a satisfactory result. Calculate the distance between transmitter and receiver.
[ Remember ]
10.
Explain the electrical properties of Ionosphere. [ Understand ]
11.
Explain the effect of earth’s magnetic field. [
Remember ]
12.
Explain Faraday rotation and whistlers. Also explain wave propagation in complex environment.
13.
Explain the mechanism of ionosphere propagation.
(APRIL / MAY 2011) [ Remember ]
14.
How does the earth affect ground wave propagation?
(APRIL / MAY 2011) [ Understand ]
15. Explain the terms (APRIL / MAY 2011), (NOV. / DEC. 2011) . [ Remember ] i). Optimum working frequency. ii). Duct propagation. iii). Virtual height iv). Skip distance
16. Discuss the effects of Earth’s magnetic field on ionosphere radio wave propagation (APRIL / MAY 2011) [ Remember ]
17. Explain the important features of ground wave propagation.
( NOV. / DEC. 2011) .
[ Remember ]
18. Describe the structure of the atmosphere and specify the factors affecting the radio wave propagation.
(MAY / JUNE 2012) [ Remember ]
19.Explain in detail about effect of earth’s magnetic field on radio wave propagation.
(MAY /
JUNE 2012)
20. i). Expalin the structure of the ionosphere with neat diagram.
( NOV. / DEC. 2011) .
[ Remember ] ii). Why do we use high frequency waves in sky wave propagation? Explain the mechanism of propagation
18.
i). Describe the tropsphere and explain how ducts can be used for microwave propagation
[ Remember ] ii). Explain the term ( NOV. / DEC. 2011) . [ Remember ] a). Optimum working frequency
28

PIT ECE VI SEM b). Skip distance c). Virtual height.
22. i). Describe the Tropo-scatter propagation. (MAY / JUNE 2012) [ Analyze ] ii). Explain the effect of Earth’s magnetic field on ground wave propagation
23. Describe the theory of propagation of Electromagnetic wave through the ionosphere in the presence of external magnetic field and show that the medium acts as doubly refracting crystal.
(MAY / JUNE 2012) [ Analyze ]
24. Describe the structure of the atmosphere and explain each layer in detail.
(MAY / JUNE 2016)
[ Analyze ]
25.
i). Discuss the effects of earth’s magnetic field on ionosphere radio wave propagation.
[ Analyze] ii). Describe the troposphere and explain how ducts can be used for microwave propagation.
(MAY / JUNE 2016) [ Analyze]
26.
Draw ' electron density profile chart of an in . Also derive an expression for the effective relative dielectric constant of the ionosphere. Explain about reflection and refraction of waves in ionosphere. ( NOV. / DEC. 2016) . [ Understand ]
27.
(i) Explain the attenuation characteristics for ground wave propagation.
28.
(ii) Explain LOS propagation and troposcatter propagation. ( NOV. / DEC. 2016) .
[ Remember ]
ASSIGNMENT QUESTIONS:
1.
What are the various types of paths of propagation of radio waves (PO1) [ Remember ]
2.
How does wave tilt occurs in ground waves.(PO1) [ Remember ]
3.
What is the difference between space wave and LOS communication(PO1) [ Remember ]
4.
What do you mean by temperature inversion & what its effects.(PO1) [ Remember ]
5.
Explain in detail about the tropo-scatter effects and duct propagation.(PO1)
6.
Tabulate the frequency ranges for the different types of communications systems. (PO7)
[ Create ]
7.
What are the components of atmosphere (PO1) [ Remember ]
8.
What is the height of D-layer and which layer is absent in night.(PO2) [ Understand ]
29

PIT ECE VI SEM
30