UNIT – IV
APERTURE AND LENS ANTENNAS
PART – A
1. State Huygen’s Principle?
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 that a secondary wave front can be constructed as the envelope of these secondary waves.
2. What is Slot Antenna?
The slot antenna is an opening cut in a sheet of a conductor, which is energized through a coaxial cable or wave guide.
3. Which antenna is complementary to the slot dipole?
The dipole antenna is the complementary to the slot antenna. The metal and air regions of the slot are interchanged for the dipole.
4. How will you find the directivity of a large rectangular broadside array?
Directivity , D = 12.56 x Area of the aperture
-----------------------------------
l2
5. What is the relationship between the terminal impedance of slot and dipole antenna?
ZsZd = ho2/4
Where Zs is the terminal impedance of the slot antenna
Zd is the terminal impedance of the dipole antenna
ho is the intrinsic impedance of the free space » 377W\\
6. What is the difference between slot antenna and its complementary dipole antenna?
1. i. Polarization are different
2. ii. The electric field be vertically polarized for the slot and horizontally polarized for its complementary dipole
3. iii. Radiation form the backside of the conducting plane of the slot antenna has the opposite polarity from that of the dipole antenna.
7. Define lens antenna?
An antenna, which collimates the incident divergent energy to prevent it from spreading in undesired directions, is called as lens antenna.
8. What are the different types of lens antenna?
1. i. dielectric lens or H plane metal plate lens
2. ii. E plane metal plate lens antenna
9. What is a dielectric lens antenna?
Dielectric lens antennas are the antennas in which the traveling wave fronts are delayed by lens media
10. What are the drawbacks of lens antenna?
* Lens antennas are used only at higher frequencies (above 3 GHz) because at lower frequencies they become bulky and heavy. Lens antennas have excessive thickness at low frequencies.
Thickness, t = l/m-1 = C/ f(m-1)
* Costlier for the same gain and beam width in comparison with reflectors
11. What are the field components that are radiated from open end of a coaxial line?
Eq = {-hbwKsinq(b2-a2)e-jbro}/8r0
Hf = {-bweKsinq(b2-a2)e-jbro}/8r0
12.What are the advantages of stepped dielectric lens antenna?
1. i. It is mechanically strong
2. ii. Reduces weight
3. iii. Less power dissipation
13.What is biconical antenna?
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 the opposite direction.
14.What is Lunenburg lens?
The Lunenburg lens is a spherical symmetric delay type lens formed from a dielectric with index of refraction ‘n’ which varies as a function of radius given by
.n = Ö[2 –{ r/R}2]
where r = radial distance from the center of the sphere
R = radius of the sphere
15.What are the advantages of lens antenna?
1. i. the lens antenna, feed and feed support do not block the aperture as the rays are transmitted away from the feed
2. ii. It has greater design tolerance
3. iii. It can be used to feed the optical axis and hence useful in applications where a beam is required to be moved angularly with respect to the axis.
16.Mention the uses of lens antenna?
1. i. Unstepped dielectric lens is a wide band antenna as its shape does not depend on the wavelength and hence it can be used over a wide frequency range, however this is not true for the dielectric lens antenna which is frequency sensitive.
2. ii. Both reflectors and lens antenna are commonly used above 1000 MHz. Lens antenna is a microwave device. So it is preferred to be usually above 3000 MHz and not below it.
17.How spherical waves are generated?
When a voltage V is supplied at the input terminals of a biconical antenna, it will produce outgoing spherical waves. The biconical antenna acts as a guide for spherical waves.
18.Define the characteristic impedance of biconical antenna?
The Characteristic impedance Zc of a biconical antenna is the ratio of voltage (r ) and current ( r )
Zc = V( r) / I ( r) = 120ln cot(a/4)
19.Bring out the expressions for voltage across the feed points of the biconical antenna and current flowing through the surface of the cone?
V(r ) = 2hHmln cot(a/4)
I( r) = 2pHmee-jbr
20.What do you meant by sect oral horn?
If flaring (opened out) is done only in one direction, then it is called as a sectoral horn.
21.What do you meant by pyramidal horn?
If flaring is done along both the walls( E & H), then it is called as a pyramidal horn.
22.What is back lobe radiation?
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.
23.What are the various feeds used in reflectors?
1. i. Dipole antenna
2. ii. Horn feed
3. iii. End fire feed
4. iv. Cassegrain feed
24.What are the different types of horn antennas?
1. i. Sectoral horn
2. ii. Pyramidal horn
3. iii. Conical horn
4. iv. Biconical horn antenna
25.Define refractive index of lens antenna?
Refractive index, m = (Velocity of wave in air)/(velocity of wave in lens medium)
26.What are secondary antennas? Give examples?
Antennas that are not radiators by themselves are called secondary antennas. For example Cassergrain, Hyperbolic antennas.
PART – B
1. Explain the different types of lens antenna? (10)
2. Explain the radiation from a rectangular aperture? (16)
3. Explain the radiation from an elemental area of a plane wave or
explain the radiation from a Huygen’s source ? (16)
4. Describe the parabolic reflector used at micro frequencies? (16)
5. Write short notes on Lunenburg lens? (16)
6. Discuss about spherical waves and biconical antenna? (16)
7. Derive the various field components radiated from circular aperture
and also find beam width and effective area ? (12)
8. Derive the field components radiated from a thin slot antenna in an
infinite cylinder ? (10)
9. Show the relationship between dipole and slot impedances? (8)
10. Explain the radiation from the open end of a coaxial cable? (8)
KEYWORDS:2009 ANNA UNIVERSITY CHENNAI B.E ELECTRONICS & COMMUNICATION ENGINEERING EC1352 (UNIT IV) QUESTION PAPER,ANNA UNIVERSITY QUESTION PAPER,ANNA UNIVERSITY,ANNA UNIVERSITY CHENNAI,ANNA UNIVERSITY COIMBATORE,ANNA UNIVERSITY TRICHY,ANNA UNIVERSITY TIRUNELVELI,ANNA UNIVERSITY MADURAI,ANNA UNIVERSITY SYLLABUS,ANNA-UNIVERSITY RESULTS,ANNA UNIVERSITY DISTANCE EDUCATION,ANNA UNIVERSITY MBA-CENTRE FOR DISTANCE EDUCATION,ANNA UNIVERSITY SCHEDULE OF EXAMINATIONS,ANNA UNIVERSITY ADMISSION,ANNA UNIVERSITY COURSES,ANNA UNIVERSITY ACADEMIC,ANNA UNIVERSITY DEPARTMENTS,ANNA UNIVERSITY RESEARCH,ANNA UNIVERSITY MAIL,ANNA UNIVERSITY QUESTION PAPERS,ANNA UNIVERSITY COUNSELLING DATES,ANNA UNIVERSITY RE-EVALUATION RESULTS
APERTURE AND LENS ANTENNAS
PART – A
1. State Huygen’s Principle?
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 that a secondary wave front can be constructed as the envelope of these secondary waves.
2. What is Slot Antenna?
The slot antenna is an opening cut in a sheet of a conductor, which is energized through a coaxial cable or wave guide.
3. Which antenna is complementary to the slot dipole?
The dipole antenna is the complementary to the slot antenna. The metal and air regions of the slot are interchanged for the dipole.
4. How will you find the directivity of a large rectangular broadside array?
Directivity , D = 12.56 x Area of the aperture
-----------------------------------
l2
5. What is the relationship between the terminal impedance of slot and dipole antenna?
ZsZd = ho2/4
Where Zs is the terminal impedance of the slot antenna
Zd is the terminal impedance of the dipole antenna
ho is the intrinsic impedance of the free space » 377W\\
6. What is the difference between slot antenna and its complementary dipole antenna?
1. i. Polarization are different
2. ii. The electric field be vertically polarized for the slot and horizontally polarized for its complementary dipole
3. iii. Radiation form the backside of the conducting plane of the slot antenna has the opposite polarity from that of the dipole antenna.
7. Define lens antenna?
An antenna, which collimates the incident divergent energy to prevent it from spreading in undesired directions, is called as lens antenna.
8. What are the different types of lens antenna?
1. i. dielectric lens or H plane metal plate lens
2. ii. E plane metal plate lens antenna
9. What is a dielectric lens antenna?
Dielectric lens antennas are the antennas in which the traveling wave fronts are delayed by lens media
10. What are the drawbacks of lens antenna?
* Lens antennas are used only at higher frequencies (above 3 GHz) because at lower frequencies they become bulky and heavy. Lens antennas have excessive thickness at low frequencies.
Thickness, t = l/m-1 = C/ f(m-1)
* Costlier for the same gain and beam width in comparison with reflectors
11. What are the field components that are radiated from open end of a coaxial line?
Eq = {-hbwKsinq(b2-a2)e-jbro}/8r0
Hf = {-bweKsinq(b2-a2)e-jbro}/8r0
12.What are the advantages of stepped dielectric lens antenna?
1. i. It is mechanically strong
2. ii. Reduces weight
3. iii. Less power dissipation
13.What is biconical antenna?
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 the opposite direction.
14.What is Lunenburg lens?
The Lunenburg lens is a spherical symmetric delay type lens formed from a dielectric with index of refraction ‘n’ which varies as a function of radius given by
.n = Ö[2 –{ r/R}2]
where r = radial distance from the center of the sphere
R = radius of the sphere
15.What are the advantages of lens antenna?
1. i. the lens antenna, feed and feed support do not block the aperture as the rays are transmitted away from the feed
2. ii. It has greater design tolerance
3. iii. It can be used to feed the optical axis and hence useful in applications where a beam is required to be moved angularly with respect to the axis.
16.Mention the uses of lens antenna?
1. i. Unstepped dielectric lens is a wide band antenna as its shape does not depend on the wavelength and hence it can be used over a wide frequency range, however this is not true for the dielectric lens antenna which is frequency sensitive.
2. ii. Both reflectors and lens antenna are commonly used above 1000 MHz. Lens antenna is a microwave device. So it is preferred to be usually above 3000 MHz and not below it.
17.How spherical waves are generated?
When a voltage V is supplied at the input terminals of a biconical antenna, it will produce outgoing spherical waves. The biconical antenna acts as a guide for spherical waves.
18.Define the characteristic impedance of biconical antenna?
The Characteristic impedance Zc of a biconical antenna is the ratio of voltage (r ) and current ( r )
Zc = V( r) / I ( r) = 120ln cot(a/4)
19.Bring out the expressions for voltage across the feed points of the biconical antenna and current flowing through the surface of the cone?
V(r ) = 2hHmln cot(a/4)
I( r) = 2pHmee-jbr
20.What do you meant by sect oral horn?
If flaring (opened out) is done only in one direction, then it is called as a sectoral horn.
21.What do you meant by pyramidal horn?
If flaring is done along both the walls( E & H), then it is called as a pyramidal horn.
22.What is back lobe radiation?
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.
23.What are the various feeds used in reflectors?
1. i. Dipole antenna
2. ii. Horn feed
3. iii. End fire feed
4. iv. Cassegrain feed
24.What are the different types of horn antennas?
1. i. Sectoral horn
2. ii. Pyramidal horn
3. iii. Conical horn
4. iv. Biconical horn antenna
25.Define refractive index of lens antenna?
Refractive index, m = (Velocity of wave in air)/(velocity of wave in lens medium)
26.What are secondary antennas? Give examples?
Antennas that are not radiators by themselves are called secondary antennas. For example Cassergrain, Hyperbolic antennas.
PART – B
1. Explain the different types of lens antenna? (10)
2. Explain the radiation from a rectangular aperture? (16)
3. Explain the radiation from an elemental area of a plane wave or
explain the radiation from a Huygen’s source ? (16)
4. Describe the parabolic reflector used at micro frequencies? (16)
5. Write short notes on Lunenburg lens? (16)
6. Discuss about spherical waves and biconical antenna? (16)
7. Derive the various field components radiated from circular aperture
and also find beam width and effective area ? (12)
8. Derive the field components radiated from a thin slot antenna in an
infinite cylinder ? (10)
9. Show the relationship between dipole and slot impedances? (8)
10. Explain the radiation from the open end of a coaxial cable? (8)
KEYWORDS:2009 ANNA UNIVERSITY CHENNAI B.E ELECTRONICS & COMMUNICATION ENGINEERING EC1352 (UNIT IV) QUESTION PAPER,ANNA UNIVERSITY QUESTION PAPER,ANNA UNIVERSITY,ANNA UNIVERSITY CHENNAI,ANNA UNIVERSITY COIMBATORE,ANNA UNIVERSITY TRICHY,ANNA UNIVERSITY TIRUNELVELI,ANNA UNIVERSITY MADURAI,ANNA UNIVERSITY SYLLABUS,ANNA-UNIVERSITY RESULTS,ANNA UNIVERSITY DISTANCE EDUCATION,ANNA UNIVERSITY MBA-CENTRE FOR DISTANCE EDUCATION,ANNA UNIVERSITY SCHEDULE OF EXAMINATIONS,ANNA UNIVERSITY ADMISSION,ANNA UNIVERSITY COURSES,ANNA UNIVERSITY ACADEMIC,ANNA UNIVERSITY DEPARTMENTS,ANNA UNIVERSITY RESEARCH,ANNA UNIVERSITY MAIL,ANNA UNIVERSITY QUESTION PAPERS,ANNA UNIVERSITY COUNSELLING DATES,ANNA UNIVERSITY RE-EVALUATION RESULTS