1. Find the Effective Length of a Λ/2 Dipole and Λ/4 Monopole. Hence Calculate Their

UNIT-1

1. Find the effective length of a λ/2 dipole and λ/4 monopole. Hence calculate their directivities, using the

appropriate radiation resistances. [10M/S1,S3]

2 (a) Establish the relations between directivity and effective area, directivity and effective length.

(b) An antenna has a radiation resistance of 63 ohms and a lossy resistance of 6ohms. If the power gain is 30,

Calculate the directivity and the efficiency of the antenna. [10M/S2]

3. What is the maximum effective aperture(approximately) for a beam antenna having half power widths of 300

and 350 in perpendicular planes intersecting in the beam axis, minor lobes are small and may be neglected.

[10M/S4]

4. (a) Define Directivity and Gain of an antenna. Bring out the relation between Directivity and Gain.

(b) The Normalized field pattern of an end fine array is given by En=Sin(π/2N)Sin(nψ/2)/Sin(ψ/2)

where ψ =dr (cosφ -1)- π/n, dr= π/2, n=10. i. Calculate the Gain G

ii. Calculate the Approximate Gain. [09M/S1]

5. (a) Explain the significance of principal planes in the description of Radiation pattern of antennas. Hence

define and distinguish between: Horizontal and vertical plane patterns, E & H plane patterns.

(b) For a source with radiation intensity u = 6 Cosθ, find the directivity and HPBW, when its pattern is uni

directional. [09M/S2]

6. (a) Define antenna beam width and directivity and obtain the relation between them.

(b) Calculate the electric field due to an isotropic radiator radiating 3 kW power at a distance of 2 Km

from it. [09M/S3]

7. (a) Define the terms:

i. Beam Width ii. Side Lobe Level

iii. Polarization iv. Effective Aperture Area. [09M/S4]

(b) What is the effective length of an antenna. Determine the effective length of a half wave dipole antenna.

8. (a) As related to antennas, define and explain the following terms:

i. Gain ii. Directivity iii. radiation resistance iv. effective area

v. effective length vi. Efficiency vii. beam width viii. bandwidth.

(b) Evaluate the directivity of i. an isotropic source, and

ii. source with bi-directional cos θ power pattern. [08N/S1,S4]

9. (a) Define and explain the significance of the terms: Radiation intensity, Beam area, Beam efficiency,

effective height, and resolution.

(b) A source has a constant power pattern limited to top half of the hemisphere only. Find its directivity and

effective area. [08N/S2]

10.(a) From the knowledge of Directive gain ‘Gd’, Prove the following relation. Gd = 120Π2/Rred (le/λ)2 Where

le= effective length of the antenna Rred = Radiation resistance of the antenna.and state the importance of

this relation.

(b) A source has bidirectional power pattern with a radiation intensity of U = 4sin θ. Find its directivity and

HPBW, sketching the pattern. [08N/S3]

11.(a) Define and Explain: Directivity and power gain for an antenna. What is the relation between the two?

Prove that the directivity of a λ/2 aerial is 0.39 db more than that of short dipole.

(b) What are principal planes? How the antenna beam width is defined in such planes? [08N/S1,S3]

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

i. Radial Power Flow ii. Radiation resistance for a short dipole iii. Uniform Current Distribution.

(b) Calculate the following for an antenna carrying 50A (rms) at 480 kHz having effective length of

60.96 metres. Take loss resistance of the antenna= 5 ohms i. Radiation resistance ii. Power radiated

iii. Antenna efficiency iv. Directivity and power gain v. HPBW and BWFN. [08N/S2,S4]

UNIT-2

1. (a) What is radiation resistance of an antenna.

(b) Show that the radiation resistance of half wave dipole is 73 ohm

2. (a) Explain the terms Isotropic, Directional and Omni directional patterns.

(b) Show that the radiation resistance of a λ/4 monopole is 36.5 ohms. [10M/S2]

3. (a) Explain the complimentary behavior between Slot and Dipole Antennas. [10M/S3]

(b) State Reciprocity Theorem. How is it useful to obtain radiation characteristics of Antennas?

4. (a) Explain the concept of retarded potential

(b) Write down the expressions for the Electric and Magnetic fields caused to an alternating current element.

Identify the Electrostatic, Induction, and Radiation terms [10M/S4]

5. (a) Derive an expression for radiance resistance of current element starting from the expression for radiation

fields.

(b) Prove that the impedance of an isolated antenna when used for receiving is same as when used for

transmitting.. [09M/S1]

6. (a) Define the following terms:

i. Directivity ii. Gain iii. Effective Aperture of Antennas.

(b) Show that the Directivity of an elementary Dipole (Current Element) is 1.5 or 1.76 dB.

1.64 respectively. [09M/S1] [08N/S3]

7. (a) State the Reciprocity Theorem for Antennas? Prove that the Self Impedance of an Antenna in transmitting

and receiving mode is same. [09M/S1]

(b) Define Directivity. Obtain the Directivity of an Isotropic Antenna, Short Dipole and Half-Wave Dipole.

8. (a) Assuming the expression of radiation fields for alternating current element,find out its radiation

resistance. Explain the significance of the term Rr.

(b) An antenna whose effective height is 100 meters at a frequency of 60 kHz radiated 100 kWof power.

Determine the strength of the electric field at a distance of 100 km from the antenna. Neglect the ground

effect and atmospheric losses. [09M/S1]

9. (a) Derive an expression for the Radiation Resistance of a Loop Antenna.

(b) Find the Effective Length of a Half Wave Dipole.

element. Assuming that the current is 10 Amp.Calculate the power radiated and radiation resistance of the

Antenna. [08N/S1]

10.(a) Explain the terms ‘Radiation Field’, ‘Induction Field’ and ‘Electrostatic Field’ by deriving the E Field of

a current element through vector potential.

(b) What is Polarization? How many types of Polarizations are used in Antennas? Explain. [08N/S2]

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

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

(b) Obtain the relative amplitudes of radiation, induction and electro-static fields at a distance of 2λ from a

short current element having an uniform current of 1 mA along its length. [08N/S1,S2,S3]

12.(a) State the following antenna theorems and bring out their importance in antenna measurements :

i. Reciprocity theorem. ii. Maximum power transfer theorem.

(b) A half wave transmitting antenna radiates 10KW of power at 100 MHz.If the heights of transmitting and

receiving antennas are 100m and 9m, calculate the power received at a distance of 10 kms from the

transmitting antenna. [08N/S4]

13.(a) Show that the radiation resistance of a small loop is equal to 320π 4(A/λ2) ohms where A is loop area.

(b) What is Folded Dipole ? Find its Radiation Resistance. [07N/S1]

14.(a) Explain the terms ‘Radiation Field’, ‘Induction Field’ and ‘Electrostatic Field’ by deriving the E Field of

a current element through vector potential.

(b) What is Polarization? How many types of Polarizations are used in Antennas? Explain. [07N/S2]

UNIT-3

1. (a) What is Array Factor? Find the array factor of 2 element array.

(b) For an array of 2 identical infinitesi8mal dipoles oriented with a separation of ‘D’ and phase excitation

Difference ‘β’ between the elements. Find the angles of observation where the nulls of the array occur.

The magnitude of excitation of the elements is same. [10M/S1][08N/S1,S3]

2. (a) A linear broadside array consist of 4 identical equal in phase point source with λ/3 spacing. Calculate

And plot the field pattern. Also find the directivity and beam width.

(b) What is optimum spacing used in parasitic array? Why. [10M/S2][07N/S1]

3. (a) Compare the performance of Broadside and End fire array.

(b) Show that the width of principle lobe of an end array is greater than that of broadside array of the same

length. [10M/S3]

4. (a) Compare the radiation characteristics of uniform linear arrays, fed with

i. Uniform amplitudes. ii. Triangular taper amplitudes.

iii. Binomially tapered amplitudes.

(b) Mention the advantages and disadvantages of Binomial array. [10M/S4][08NN/S2]

5. (a) Explain the principle of stacked arrays

(b) Obtain the array factor of a binomial array of 6 isotropic radiators. [09M/S1]

6. (a) Derive an expression for field pattern of a 2 element array and draw the field pattern

i. When d= λ/2 and α=00 ii. When d= λ/2 and α=1800

(b) Explain Dolph-Tchebyshelf distribution for linear broadside array. [09M/S2]

7. Evaluate the radiation characteristics HPBW, Null, Side lobe positions. And actual side lobe levels for a

Uniform linear array of 10 elements with quadrate wavelength spacing fed with α= 2πd/λ. Sketch the pattern.

What happens if α= (-2πd/λ)-π/10. [09M/S3]

8. (a) Compute the principle beam width for broadside and end fire array.

(b) A uniform linear array consisting of isotropic radiators spaced half wavelength a parts has 10 elements,

elements, each element carries 0.5amperes. Calculate the width of principle beam and maximum power

radiated if operated as i. Broadside array ii. End fire array. [09M/S4]

9. (a) Derive an expression for radiated power(Rp) of a BSA with ‘n’ vertical dipoles. Plot the Rp in vertical and

vertical and horizontal planners for a BSA of 4 dipoles.

(b) Show the directivity of EFA (with increased directivity) is given by 1.789[4(L/λ)]. [08N/S1]

10.(a) Find the radiation pattern of 4 isotropic elements fed in phase, spaced λ/2 a part by using pattern

multiplication.

(b) What is uniform linear array? Discuss the application of linear array. [08N/S2]

11.(a) Enumerate the advantages and disadvantages of linear arrays.

(b) Find the phasing requ8ired to steer a beam Zenith to-400 for a 5 ele4ment array with 0.4λ inter element

spacing. [08N/S3]

12. (a) Explain the concept of scanning arrays.

(b) Show that Dolph-Tchebyshelf distributions gives optimum distribution and minimum side lobe level for

a given beam width of major lobe. [08N/S4]

13.(a) Compare the radiation characteristics of BSA’s, EFA’s, EFA’s with increased directivity, and Binomial

arrays. Under what conditions they are preferred?

(b) What are the conditions for the linear array of 20 isotropic elements to radiate in end fire, broad side

Modes and Hansen-word yard array mode? [08/N/S4]

14.(a) In order to scan the beam of a linear array to 300 off broadside. Calculate the inner element phase shift

Required if the elements are spaced at 3 cms and the frequency is 64 KHz.

(b) What are the linear arrays? Compare Broadside array and End fire array. [07N/S2]

15.(a) Explain the procedure for measuring the radiation pattern of a half wave dipole.

(b) What is the requirement for tapering of arrays.

UNIT-4

1.(a) State the advantages and disadvantages of Rhombic Antenna.

(b) Draw the radiation pattern for traveling wave antenna for L=λ/2, λ, 2λ, 4λ and 8λ. [10M/S1]

2.(a) If a Helical antenna has spacing between turns 0.05m, diameter 0.1m,number of turns equal to 20 and

operates at 1000MHz. find the null to beam width of the main beam and also half power beam width and

directivity.

(b) Discuss the basic properties of Helical Antennas. [10M/S2]

3. (a) Describe the construction and properties of Rhombic Antenna.

(b) Describe the characteristics of long wire traveling wave antenna. Sketch their pattern for lengths of

i. λ/2ii. 5λ iii. 20λ [10M/S3]

4. (a) Design a Rhombic Antenna to operate at 20MHz when the angle of elevation Δ=100

(b) Describe the Non Resonant V-antenna [10M/S4]

5. (a) Sketch the current distribution in vertical grounded antennas of λ/4 and 3λ/4 length.

(b) Derive an expression for radiation pattern of a rhombic antenna. At what frequencies rhombic antenna is

used. [09M/S1]

6. (a) Explain the radiation from traveling wave antennas.

(b) Describe the design and performance of Rhombic antennas

7. (a) Write short notes on “Helical Antenna”. [09M/S3][08N/S2]

(b) Derive an expression for radiated electric field strength of a traveling wave radiation of length ‘1’.

8. (a) Explain the construction of Rhombic Antenna with balloon and termination. Draw the radiation pattern of

rhombic antenna i. Over perfectly conducting plane.

ii. In the presence of earth.

(b) Derive electric field expression for Non Resonant antenna. [09M/S4]

9. (a) Derive an expression for electric field of a Non Resonant antenna of length ‘1’ carrying current.

(b) Sketch and explain the constructional features of a Helical antenna. [08N/S1][07N/S2]

10. (a) What is meant by Non Resonant antenna? Derive from the first principle, the field due to such antenna

and sketch the field pattern for lengths λ and 2λ.

(b) Mention the merits and demerits of a traveling wave antenna. [08N/S3]

11. (a) Distinguish between

i. Resonant and Non Resonant antennas ii. Narrow Band and wide Band antennas. [08N/S4]

12. (a) Compare the requirements and radiation characteristics of resonant and non-resonant radiators?

(b) Determine the lengths and spacing requirements for a 3 element yagi-Uda antenna array at 500mHz, and

explain its characteristics. [08N/S1]

13. (a) With neat schematics, describe the principle of working of a 3 element yagi antenna, listing out its length

and spacing requirements.

(b) Sketch the current distribution on a folded dipole, and account for its input impedance when the two legs

have unequal diameters. [08N/S2]

14. Write notes on:

(a) Parasitic elements and their reference (b) Terminated antennas

15. (a) Explain the need and the configuration of a folded Dipole Antenna. Sketch its radiation pattern and

compare its characteristics with those of a simple λ/2 dipole

(b) List out the design relations associate with a Rhombic Antenna. What are its applications? [08N/S4]

16 (a) Write short notes on “Helical Antenna” [07N/S1]

(b) Derive an expression for radiated electric field strength of a traveling wave radiation of lengthy ‘1’.

17. (a) Distinguish between Traveling wave and Standing wave antennas.

(b) Compare Resonant and Non Resonant antennas.

18. Explain how a Yagi Uda antenna is analyzed as an EFA, listing and the necessary mathematical relations.

Why is it called a super Gain Antenna? [07N/S4]

UNIT-5

1. (a) What is a parabolic element. How does a parasitic element act when length is greater than and smaller

than λ/2.

(b) Distinguish between Spherical and Cylindrical paraboloids. Comment on their aperture efficiency

and applications. [10M/S1][08M/S1]

2. (a) Explain all the structural requirements of a 5 element yagi antenna at 475 MHz accounting for typical

spacing, length to diameter ratios and input impedance Zn.

(b) Explain the geometry, requirements and properties of parabolic reflectors. [10M/S2]

3. (a) A paraboloid operating at 5 GHz, has a radiation pattern with null to null beam width of 100. Find the

mouth diameter of the paraboloid, HPBW and power gain.

(b) Draw the Yadi-Uda antenna and sketch its radiation, Write down the design equations of yagi-uda

antenna. [10M/S3]

4. (a) Describe the following reflectors :i. Truncated Paraboloid ii. Offset Paraboloid.

(b) Find the gain, BWFN, HPBW of a paraboloid of 2 m diameter operating at 5GHz when half wave

dipole is used. [10M/S4]

5. (a) Explain the working of Yagi Antenna.

(b) Compare Corner reflector and Parabolic reflector. [09M/S1]

6. (a) Write short notes on ‘Folded Dipole’.

(b) A six feet parabolic reflector is to be used at 6 GHz. Calculate the beam width between first nulls and

gain of the antenna in dB. [09M/S2]

7. (a) With reference to paraboloids, explain i. Aperture Blocking. ii. FID ratio. iii. Spill over.

(b) Evaluate the power gain directing and the required diameter of a paraboloid having a null beam width

of 100 at 3 GHz. [09M/S3]

8. (a) For what mouth diameter and capture area of a paraboloid reflector is a BWFN of 120 obtained when

it is operated at 2.5 GHz.

(b) Describe the cassegrain feed mechanism of a parabolic reflectors. [09M/S4]

9. (a) Describe the performance of paraboloids with respect to aperture blocking. [08M/S1]

(b) Describe the constructional details of cassegrain antennas and sketch its radiation characteristics.

10.(a) A Paraboloid reflector of 1.8 m diameter is used at 6 GHz. Calculate the beam width between the

nulls and gains in dBs.

(b) Design Yagi Uda antenna of six elements to provide a again of 12dB if the operating frequency is

200 MHz. [08M/S3]

11.(a) A paraboloid reflector has radiation characteristics whose HPBW is 50. Find out its null to null beam

width and power gain.

(b) Discuss the conditions under which a parasitic dipole placed near and parallel to a driven dipole can

act as a reflector. [08M/S4]

12.(a) Establish and explain the gain and beam width relations for a parabolic reflector and account for its

beam shaping considerations.

(b) Write short notes on: Cassegrainian antennas. [07M/S1,S2]

13.(a) Sketch the typical geometry of a helical antenna radiating in axial mode, and list out all its

parameters and basic characteristics. List out the expressions for BWFN, directivity and axial ratio.

(b) With a neat sketch, explain the image formation and field calculation for the case of a 600 corner

reflector. [07M/S3]

14.(a) With sequence to helical antennas, explain the following features: i. band width

ii. circular polarization iii. linear polarization under axial mode.

(b) Distinguish between the F/B and f/D ratios for a parabolic reflector. [07M/S4]

UNIT_6

1. (a) Describe the method of measuring the gain and radiation pattern of an antenna.

(b) A standard gain horn antenna with a power gain of 12.5, is used to measure the gain of a large

directional antenna by comparison method. The test antenna is connected to the receiver and an

attenuator adjusted to 23dB in order to have the same receiver output. Find out the gain of the large

antenna. [10M/S1]

2. (a) Explain why the beam widths in the two perpendicular planes of radiation of a square pyramidal

horn will be different. Derive gain formula.

(b) What is an antenna test range? What is minimum distance at which test should be taken for an

antenna 5m in diameter and working at 6GHz? Derive the necessary expression. [10M/S2]

3. (a) Given that radiation pattern of an antenna are measured, explain how the directivity and power gain

can be evaluated.

(b) Distinguish between different types of lens antennas, explaining their curvature profiles. [10M/S3]

4. (a) Derive an expression for directivity of pyramidal horn in terms of aperture dimensions. [10M/S4]

(b) Explain the 3 antenna method of measurement of the gain of a horn antenna with necessary relations.

5. (a) Explain radiation through aperture horn antenna and reflector antenna.

(b) Write short notes on “Antenna Pattern Measurement”. [09M/S1,S2]

6. (a) Describe the measurement procedures to obtain directive gain of an antenna. State clearly the

precautions taken with necessary justifications.

(b) Describe the “Dielectric Lens”. [09M/S3] 7. (a) What is an electromagnetic horn antenna? What are its applications? The length of an E-plane

sectoral horn is 15cms. Design the horn dimensions such that it is optimum at 10GHz. [09M/S4]

8. (a) What is an Optimum Horn? Sketch and Explain its characteristics along with dimensional relations.

(b) Explain the first transmission formula and its applicability for antenna gain measurements. [08M/S1]

9. (a) What is the principle of equality of path length? How is it applicable to horn antenna?