antenna & wave propagation

ANTENNAS AND WAVE PROPAGATION L T P M C3 1 0 100 4

UNIT I RADIATION PROPERTIES 9 Concept of vector potential- Modification for time varying- retarded case- Fields associatedwith Hertzian dipole- Power radiated and radiation resistance of current element-Radiationfrom half-wave dipole and quarter-wave monopole antennas. Radiation intensity- Directivegain- Directivity- Power gain- Beam Width- Band Width- Gain -Quarter wave monopole-Halfwavedipole and folded dipole- Reciprocity principle- Effective length and Effective area-Relation between gain effective length and radiation resistance.UNIT II ANTENNA ARRAYS 9Antenna Arrays: Expression for electric field from two, three and N element arrays- lineararrays: Broad-side array and End-Fire array- Method of pattern multiplication- Binomial array-Horizontal and Vertical Antennas above the ground plane, Phased arrays, Frequency-Scanning arrays- Adaptive arrays and Smart antennas.UNIT III ANTENNA TYPES 9Loop Antennas: Radiation from small loop and its radiation resistance- Radiation from a loopwith circumference equal to a wavelength-Helical antenna: Normal mode and axial modeoperation-Yagi uda Antenna- Log periodic antenna- Phased array- rhombic antenna- Hornantenna- Reflector antennas and their feed systems- Micro strip antenna-Selection ofantenna based on frequency of operation – Antennas for special applications: Antenna forterrestrial mobile communication systems, GPR, Embedded antennas, UWB, Plasmaantenna.UNIT IV WAVE PROPAGATION 9Ground wave propagation: Attenuation characteristics for ground wave propagation-Calculation of field strength at a distance - Space wave propagation: Reflection from groundfor vertically and horizontally polarized waves- Reflection characteristics of earth- Resultant ofdirect and reflected ray at the receiver- Duct propagation - Sky wave propagation: Structureof the ionosphere- Effective dielectric constant of ionized region- Mechanism of refraction-Refractive index- Critical frequency- Skip distance- Effect of earth’s magnetic field-Attenuation factor for ionospheric propagation- Maximum usable frequency- Fading andDiversity reception.UNIT V ANTENNA AND IONOSPHERIC MEASUREMENTS 9Antenna Measurements:Reciprocity in Antenna measurements – Near-field and Far-field - Measurementsranges - Measurement of different Antenna parameters- Directional pattern, Gain,Phase, Polarization, Impedance, Efficiency.Ionosphere Measurements:Measurement of vertical Incidence- Group Velocity and Group Delay- Relation betweenoblique and vertical Incidence transmission.TOTAL: 45TUTORIAL : 15REFERENCES:1. John D-Kraus and Ronalatory Marhefka- "Antennas"- Tata McGraw-Hill Book Company-2002-2. E-C-Jordan and Balmain- "Electro Magnetic Waves and Radiating Systems"- PHI- 1968-Reprint 2003-3. R-E-Collins- 'Antennas and Radio Propagation "- McGraw-Hill- 1987-4. Ballanis "Antenna Theory " - John Wiley & Sons- second edition – 20035. D.Ganesh rao, B.Somanathan nair, Deepa Reghunath- “Antennas and Radio-WavePropagation”, Sanguine technical publishers, Bangalore- 2007.

KSRCE/ECE ANTENNA AND WAVE PROPAGATION

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERINGK.S.R. COLLEGE OF ENGINEERING: TIRUCHENGODE – 637 215.

COURSE / LESSON PLAN SCHEDULE

NAME : J.GNANAMBIGAI CLASS: III -ECE (A &B SECTION)SUBJECT : ANTENNA S AND WAVE PROPAGATION REFERENCES:

1.E.C.Jordan and Balmain : “Electro magnetic Waves and Radiating Systems” –Prentice Hall of India – 1968,Reprint 2003.(Unit I,V)2.. John.D.Krauss and Ronalatory Marhefka,”Antennas”,Tata Mc Graw hill Book company2002.

3. R.E.Collins,’Antennas and Radio Propagation’, Mc Graw hill-1987.4. Ballanis,”Antenna Theory”,John Wiley & sons,II edition,2003.5. K.D.Prasad.”Antenna and Wave Propagation”Tech India Publications.

C). LEGEND: L 1 - Lecture 1 BB - Black BoardT 1 - Tutorial 1 OHP - Over Head Projector Tx 1 - Text 1 pp - Pages Rx 1 - Reference 1

Sl.No.

Lecture Hour

Topics to be coveredTeaching Aid Required

Book No. / Page No.

UNIT-I RADIATION PROPERTIES

1 L 1Concept of vector potential,

BBRx 1/pp-90-92,Rx5/pp-274,415,

2 L 2Modification for time varying,retarded case

BBRx 1/pp-94Rx5/pp-298

3 L 3Fields associated with Hertzian Dipole

BBRx 1/pp-323-325,Rx 5/pp-423,

4. L 4Power radiated and radiation resistance of current element BB

Rx 1/pp-323-325,Rx 5/pp-445-448

5. T-1 Problems BB

6. L 5Radiation resistance of elementary dipole with linear current distribution

BBRx 1/pp-326Rx 5/pp-435

7.L 6

Radiation from half wave dipole&quarter wave monopole

OHPRx 1/pp-328Rx 5/pp-452,438

8. L7RadiationIntensity, Directive gain, Directivity, Power gain, Beamwidth,Band width, BB

Rx 1/pp-374,353,602Rx4/pp-35,39,62Rx 5/pp-536-574

9. L8Halfwave dipole, quarter wave monopole, Folded dipole

BBRx 5/pp-452,438Rx 1/pp-127, 374,

10. L9Reciprocity principle, Effective length&effective area, Relation between gain effective length and radation resistance.

BBRx 1/pp-353,602Rx4/pp-35,39,62Rx 5/pp-536-574

11. T 2 Problems BB

12. L10Radiation resistance of various wire antennas and short dipoles BB

Rx 1/pp-326Rx 5/pp-435


UNIT-II ANTENNA ARRAYS

13. L 11Expression for electric field from two & three element arrays,

Rx4/pp-224Rx 5/pp-723

14. L 12BSA,EFA ,Uniform linear array

BBRx1/pp-362Rx4/pp-257

15. L13Method of pattern multiplication

BBRx1/pp-372Rx4/pp-288Rx 5/pp-635

16. L 14Binomial array,Horizontal& Vertical antennas above ground the ground plane.

BBRx 5/pp-276-278

17. L 15Phased arrays,frequency Scanning arrays

BBRx 5/pp-626Rx 2/pp-572,576

18. L 16 Adaptive Arrays& Smart antennas OHP Rx 2/pp-58219. T 3 Problems on arrays BB20. T-4 Problems on Radiation resistance BB21. L 17 Dolph Tchebyshev Arrays BB Rx 5/pp-637

UNIT-III ANTENNA TYPES

22. L 18Radiation from small loop & its radiation resistance BB

Rx 1/pp-374,353,602Rx4/pp-35,Rx 5/pp-736

23. L 19Radiation from a loop with circumference equal to a wavelength BB

Rx 5/pp-723

24. L 20Helical antenna,Normal mode &axial mode operation BB

Rx4/pp-228Rx 5/pp-791-796

25. L 21Yagi uda antennas

BBRx 4/pp-505,506Rx 5/pp-777-779

26. L 22

Log periodic antenna.LPDA

BB

Rx1/pp-606Rx 5/pp-779Rx1/pp-608Rx 5/pp-781

27. L 23Analysis of Rhombic antenna. Design of Rhombic antennas. BB

Rx 4/pp-492Rx 5/pp-710-712

28. L 24Horn antenna

BBRx 4/pp-651Rx 5/pp-785

29. L 25Reflector type of antennas (dish antennas).& their feed systems BB

Rx 4/pp-347Rx 5/pp-829-838

30. L 26 Micro Strip antennas BB Rx 5/pp809

31. L 27Selection of antenna based on frequency of operation,Antennas for special applications BB

Rx 2/pp 708

32. L 28Antenna for terrestrial mobile communication systems,GPR OHP

Rx 2/pp 708-712Rx 2/pp 781

33. T-6Embedded antennas,UWB antennas,Plasma antenna OHP

Rx 2/pp 784-788


UNIT-IV WAVE PROPAGATION

34. L 29Ground wave propagation: Attenuation characteristics for ground wave propagation

BBRx1/pp-651Rx 5/pp-1111

35. L 30Calculation of field strength at a distance.

BBRx1/pp-652Rx 4/pp-1109

36. L31Space wave propagation: Reflection from ground for vertically and horizontally polarized waves.

BBTx1/pp-629Rx 4/pp-1152

37. L32Reflection characteristics of earth. Resultant of direct and reflected ray at the receiver. Duct propagation.

BBTx1/pp-640Rx 4/pp-1160

38. L33Sky wave propagation: Structure of the ionosphere. Effective dielectric constant of ionized region.

BBTx1/pp-689,670Rx 4/pp-1104-1119,1135

39. L34Mechanism of refraction. Refractive index. Critical frequency. Skip distance. OHP

Tx1/pp-671,682,687Rx 4/pp-1121-1123

40. L35Effect of earth’s magnetic field. Maximum usable frequency.

BBTx1/pp-671,682,687Rx 4/pp-1134-1147

41. L36 Fading and Diversity reception BB Tx1/pp-670

42. T 7 Problems BB

43 L 37 Ionospheric Abnormalities OHP Rx 5/pp-1146-1150

UNIT-V ANTENNA & IONOSPHERIC MEASUREMENTS

44. L38Reciprocity in antenna measurements-Near & Far field

BBRx5/pp 559Rx 2/pp 39

45. L39Measurement Ranges


46. L40Measurement of different antenna parameters, Directional pattern, BB

Rx4/pp 858-872Rx 2/pp 848-866Rx5/pp 855-857

47. L41Gain,Phase,polarization,


48. L42impedance,efiiciency

BBRx 2/pp 864,866-872Rx5/pp 845,857

49. L43Ionosphere Measurements-Measurement of vertical incidence

BBRx 5/pp-1146-1150

50. L44 Group velocity & group delay BB Rx 5/pp-1146-1150

51. L45Relation between oblique & vertical Incidence Transmission.

BBRx 2/pp 864,866-872Rx5/pp 845,857

52. T 8 Problems BB

PERPARED BY HOD-ECE(J.GNANAMBIGAI) (P.S.PERIYASAMY)


K.S.R.COLLEGE OF ENGINEERING.DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING.

Antennas & Wave Propagation QUESTION BANK

UNIT-I RADIATION PROPERTIES1.What is retarded Vector potentials?

Ans: There is a finite time delay for propagation of an electromagnetic wave from a source point to the observation point.The effect of this propagation delay is introduced in vector and scalar potentials by simply substituting the time varaible ‘t’ by a variable {t-r/c}.The potentials at the observation point are delayed or retarded by this time delay are known as retarded potentials.2.Write an expression for retarded current.

[I]=Io exp(j _W-r/c))3.What are wire antennas and give it’s applications.

Ans: Dipole antenna, loop antenna, helix antenna are some of the wire antennas, It can be used on automobiles, buildings, ships, aircrafts, spacecraft etc...4.what is an infinitesimal dipole?

Ans:When the length of the short dipole is becoming small, th eterm infinitesimal dipole is used.5.What is oscillating electric dipole?

Ans:It represents alternating current element.A current element refers to filamentary current I flowing along an element’dl’ length.6.What is a Short Dipole?

Ans: A short dipole is one in which the field is oscillating because of the oscillating voltage and current.It is called so, because the length of the dipole is short and the current is almost constant throughtout the entire length of the dipole.It is also called as Hertzian Dipole which is a hypothetical antenna and is defined as a short isolated conductor carrying uniform alternating current.7.How radiations are created from a short Dipole?

Ans:The dipole has two equal charges of opposite sign oscillating up and down in a harmonicmotion.The charges will move towards each other and electric filed lines were created.When the charges meet at the midpoint, the field lines cut each other and new field are created.This process is spontaneous and so more fields are created around the antenna.This is how radiations are obtained from a short dipole8.Why a short dipole is also called an elemental dipole?

Ans:A short dipole that does have a uniform current will be known as the elemental dipole.Such a dipole will generally be considerably shorter than the tenth wave length maximum specified for a short dipole.Elemental dipole is also called as elementary dipole,elementary doublet and hertzian dipole.9.Why a short dipole is called a oscillating dipole?

Ans:A short dipole is initially in neutral condition and the moment a current starts to flow in one direction,one half of the dipole require an excess of charge and the other a deficit because a current is a flow of electrical charge.Then ,there will be a voltage between the two halves of the dipole.When the current changes its direction this charge unbalance will cause oscillations.Hence an oscillating current will result in an oscillating voltage.Since,in such dipole,electric charge oscillates ,it may be called as Oscilllating electric dipole.10.What do you understand by retarded current?

Ans: Since,the short electric dipole is so short,the current which is flowing through the dipole isassumed to be constant throughtout its length.The effect of this current is not felt instantaneous at a distance point only after an interval equal to the time required for the wave to propagate over the distance r is called the retardation time. The retarded current [I]=Io exp(j _W-r/c))11.Define induction field

Ans:The induction field will predominate at points close to the current element ,where the distance from the centre of the dipole to the particular point is less.This field is more effective in the vicinity of the current element only.It represents the energy stored in the magnetic field surrounding the current element or conductor.This field is also known as near field.12.Define Radiation field Ans:The radiation field will be produced at a larger distance from the the current element ,where the distance from the centre of the dipole to the particular point is very large.It is also called as distant field or far field.


13.At what distance from the dipole is the induction field equal to the radiation field?Ans:As the distance from the current element or the short dipole increases ,both induction and

radiation fields emerge and start decreasing .However,a distance reaches from the conductor at which both the induction and radiation field becomes equal and the particular distance depends upon the wavelength.The two fields will thus have equal amplitude at that particular distance.14.Define Radiation Resistance

Ans:It is defined as the fictitious resistance which when inserted in series with the antenna will consume the same amount of power as it is actually radiated.The antenna appears to the transmission line as a resistive component and this is known as the radiation resistance.15.Can same antenna be used satisfactorily for transmission as well as reception?

Ans:Ordinary antennas can be used to transmit and receive the signal at different times.Radar types antennas can be used to transmit and receive the signal at the same time.16.Compare radian and steridian.

Ans:Radian-measure of plane angle. Steridian- measure of solid angle.17.Name the fields around the antenna.

Ans: Near field or Fresnel Zone ii.Far field or fraunhofer zone18.Define Radiation intensity?

Ans:The power radiated from an antenna per unit solid angle is called the radiation intensity U (watts per steradian or per square degree). The radiation intensity is independent of distance.19. Define Beam efficiency?

Ans:The total beam area ( WA) consists of the main beam area ( WM ) plus the minor lobe area ( Wm) .Thus WA = WM+ Wm . The ratio of the main beam area to the total beam area is called beam efficiency.Beam efficiency = SM = WM / WA.20.Define Directivity?

Ans:The directivity of an antenna is equal to the ratio of the maximum power density P(q,f)max to its average value over a sphere as observed in the far field of an antenna.D =P(q,f)max/P(q,f)av. Directivity from Pattern. D = 4p / WA. Directivity from beam area(WA ).21.What are the different types of aperture.?Ans:i) Effective aperture.,ii). Scattering aperture,iii) Loss aperture. iv) Collecting aperture.v). Physical aperture.22.Define different types of aperture.?Effective aperture(Ae).

It is the area over which the power is extrated from the incident wave and delivered to the load is called effective aperture.Scattering aperture(As.)

It is the ratio of the reradiated power to the power density of the incident wave.Loss aperture. (Ae).

It is the area of the antenna which dissipates power as heat.Collecting aperture. (Ae). It is the addition of above three apertures.Physical aperture. (Ap).

This aperture is a measure of the physical size of the antenna.23. Define Aperture efficiency?

Ans:The ratio of the effective aperture to the physical aperture is the aperture efficiency. i.e Aperture efficiency hap = Ae/ Ap (dimensionless).24. What is meant by effective height?

Ans:The effective height h of an antenna is the parameter related to the aperture.It may be defined as the ratio of the induced voltage to the incident field.i.e H= V / E.25. What are the field zone? The fields around an antenna ay be divided into two principal regions. i.Near field zone (Fresnel zone) ii. Far field zone (Fraunhofer zone)26.What is meant by Polarization.?Ans:The polarization of the radio wave can be defined by direction in which the electric vector E is aligned during the passage of atleast one full cycle.Also polarization can also be defined the physical orientation of the radiated electromagnetic waves in space. The polarization are three types. They are Elliptical polarization ,circular polarization and linear polarization.


27. What is meant by front to back ratio.?Ans:It is defined as the ratio of the power radiated in desired direction to the power radiated in the opposite direction. i.e FBR = Power radiated in desired direction / power radiated in the opposite direction.28. Define antenna efficiency.?

Ans:The efficiency of an antenna is defined as the ratio of power radiated to the total input power supplied to the antenna. Antenna efficiency = Power radiated / Total input power29. What is radiation resistance ?

Ans:The antenna is a radiating device in which power is radiated into space in the form of electromagnetic wave. W’ = I2 R; Rr = W’/ I2 Where Rr is a fictitious resistance called as radiation resistance.30 What is meant by antenna beam width?

Ans:Antenna beamwidth is a measure of directivity of an antenna. Antenna beam width is an angular width in degrees, measured on the radiation pattern (major lobe) between points where the radiated power has fallen to half its maximum value .This is called as “beam width” between half power points or half power beam width.(HPBW).31. What is meant by reciprocity Theorem.?

Ans:If an e.m.f is applied to the terminals of an antenna no.1 and the current measured at the terminals of the another antenna no.2, then an equal current both in amplitude and phase will be obtained at the terminal of the antenna no.1 if the same emf is applied to the terminals of antenna no.2.32.What is meant by isotropic radiator?Ans:A isotropic radiator is a fictitious radiator and is defined as a radiator which radiates fields uniformly in all directions. It is also called as isotropic source or omni directional radiator or simply unipole.33. Define gain

Ans: The ratio of maximum radiation intensity in given direction to the maximum radiation intensity from a reference antenna produced in the same direction withsame input power. i.eGain (G) = Maximum radiation intensity from test antenna -------------------------------------------------------- Maximum radiation intensity from the reference antenna with same input power34. What is meant by cross field.?

Ans:Normally the electric field E is perpendicular to the direction of wave propagation. In some situation the electric field E is parallel to the wave propagation that condition is called Cross field.35.Define axial ratioAns:The ratio of the major to the minor axes of the polarization ellipse is called the Axial Ratio. (AR).36. What is meant by Beam Area.?

Ans:The beam area or beam solid angle or WA of an antenna is given by the normalized power pattern over a sphere. WA = ò ò4p Pn ( q,f ) dW Where dW = Sin q d q .df37. What is duality of antenna.?

Ans:It is defined as an antenna is a circuit device with a resistance and temperature on the one hand and the space device on the other with radiation patterns, beam angle ,directivity gain and aperture.

16 MARKS1.what is Hertzian dipole.& draw the same.(D-07)2.Derive the Expression for field components of an infinitesimal dipole(M-07)3. Derive the Expression for power radiated and find the radiation resistance of an HW dipole(M-07)4. Derive the Expression for radiated field components of an short dipole(D-07)5.Starting from first principles obtain the expression for the power radiated by a half wave dipole(D-07)6.Write an expression for power radiated of current element.7.Define radiation intensity(M-07) 8.Define directivity(M-05)9.Write the significance of notations dBi and dbd. (N-06)10.Illustrate the reciprocity theorem with its diagram. (N-07)11.Comopute the effective area and directive gain for a half wave dipole. (N-07)12.Show that reciprocity theorem can be applied to antennas. (N-06)13.Compute the folded dipole with dipole moment. (N-06)


UNIT-IIANTENNA ARRAYS

1.State Poynting theorem.Ans:It states that the vector product of electric field intensity vector E and the magnetic filed

intensity vector H at any point is a measure of the rate of energy flow per unit area at that point.The direction of power flow is perpendicular to both the electric field and magnetic field components.2.What is point source?Ans:It is the waves originate at a fictitious volumeless emitter source at the center ‘O’ of the observation circle.3.What is meant by array?An antenna is a system of similar antennas oriented similarly to get greater directivity in a desired direction.4.What is meant by uniform linear array.?

Ans:An array is linear when the elements of the array are spaced equally along the straight line. If the elements are fed with currents of equal magnitude and having a uniform progressive phase shift along the line, then it is called uniform linear array .5.What are the types of array?

a. Broad side array. b. End fire array c. Collinear array. d. Parasitic array.6.What is Broad side array?

Ans:Broad side array is defined as an arrangement in which the principal direction of radiation is perpendicular to the array axis and also the plane containing the array element. For Broad side array the phase difference 6.a.Define End fire array?

Ans:End fire array is defined as an arrangement in which the principal direction of radiation is coincides with the array axis7. What is collinear array?Ans:In this array the antenna elements are arranged coaxially by mounting the elements end to end in straightline or stacking them one over the other with radiation pattern circular symmetry. Eg. omnidirectional antenna.8. What is Parasitic array?

Ans:In this array the elements are fed parasitically to reduce the problem of feed line. The power is given to one element from that other elements get by electro magnetic coupling. Eg. Yagi uda antenna.9. What is the condition on phase for the end fire array with increased directivity?10.Define array factor.11. Define beam width of major lobe?

It is defined the angle between the first nulls (or) it is defined as twice the angle between the first null and the major lobe maximum direction.12. List out the expression of beam width for broad side array and end fire array.

For broad side array the expression for beam width between the first nulls is given by,BWFN = For End fire array the expression for beam width between the first nulls is given by,13. Differentiate broad side and End fire array?

Broad side array End fire array1. Antennas fed in Phase Antenna elements are fed of out of Phase2. Maximum Radiation is perpendicular Maximum Radiation is directed along the array axis.

to the direction of array axis.3. Beam width of major lobe is twice the Beam width is greater than that for a broad side array of

same length.14.What is the need for the Binomial array?

The need for a binomial array isi). In uniform linear array as the array length is increased to increase the directivity, the secondary lobesalso occurs. ii) For certain applications, it is highly desirable that secondary lobes should be eliminated completely or reduced to minimum desirable level compared to main lobes.


15. Define power pattern?Graphical representation of the radial component of the pointing vector Sr at a constant radius as

a function of angle is called power density pattern or power pattern.16. What is meant by similar Point sources?

Whenever the variation of the amplitude and the phase of the field with respect to the absolute angle for any two sources are same then they are called similar point sources. The maximum amplitudes of the individual sources may be unequal.17. What is meant by identical Point sources?

Similar point sources with equal maximum amplitudes are called identical point sources.18. What is the principle of the pattern multiplication?

The total field pattern of an array of non isotropic but similar sources is the product of thei) individual source pattern and ii) The array pattern of isotropic point sources each located at the phase center of the individual source having the same amplitude and phase.While the total phase pattern is the sum of the phase patterns of the individual source pattern and array pattern.19.What is the advantage of pattern multiplication? Useful tool in designing antenna approximates the pattern of a complicated array without making lengthy computations20.What is tapering of arrays?

Tapering of array is a technique used for reduction of unwanted side lobes .The amplitude of currents in the linear array source is non-uniform; hence the central source radiates more energy than the ends. Tapering is done from center to end.21.What is a binomial array?

It is an array in which the amplitudes of the antenna elements in the array are arranged according to the coefficients of the binomial series.22.What are the advantages of binomial array?

Advantage: No minor lobes Disadvantages: Increased beam width .Maintaining the large ratio of current amplitude in large arrays is difficult23.What is the difference between isotropic and non isotropic source

Isotropic source radiates energy in all directions but non-isotropic source radiatesenergy only in some desired directions. ._Isotropic source is not physically realizablebut non-isotropic source is physically realizable.24.Define Side Lobe Ratio

Side Lobe Ratio is defined as the ratio of power density in the principal or main lobe to the powerdensity of the longest minor lobe.25. List the arrays used for array tapering Binomial Array:Tapering follows the coefficient of binomial series .Dolph Tchebycheff Array: Tapering follows the coefficient of Tchebycheff polynomial 26.What are parasitic elements in an array? Elements in an array with no feeding arrangements are called parasitic elements.27.Define HPBW The half power beam width can be defined as the angle subtended by the half power points of the main lobe28.What are absolute power pattern and normalized power pattern

If the radial component is expressed in W/m2,the graph is called as an absolute ppwer pattern. A pattern with a maximum value of unity Sr/Srm is called as a normalised pattern29.What is the relationship between effective aperture and dirctivity? Do=4πAe\

16 MARKS1.Define an iostropic radiator(M-05)2..What is meant by BSA and EFA(N-07)3.Derive the gain of Half wave length antenna. (N-07)4.What is pitch angle and how it is calculated(N-07)5.Derive the expression for directivity in terms of beam solid angle(M-07)


6.Derive the expression for electric field of a BSA of 2 point sources and also find the maxima directions,minimaand half power point direction. (M-07)7.What is an antenna array? What are the types of antenna arreys,for each type explain it with array diagram and radiation pattern.8. Derive the total far field pattern for uniform linear array with ‘n’ isotropic sources.9.Obtain the expression for the field and radiation pattern produced by two element array of short dipole with distance of seperation χ/ 2 and currents of equal magnitude and phase shift 180.

UNIT-IIIANTENNA TYPES

1.What is a loop antenna?A loop antenna is a radiating coil of any convenient cross-section of one or more turns carrying

radio frequency current.it may assume any shape (e.g. rectangular,square,triangular and hexagonal)2.Give an expression of radiation resistance of a small loop

Radiation resistance of a small loop is given by Rr=31,200 (A/_ 2)23.How to increase the radiation resistance of a loop antenna

The radiation resistance of a loop antenna can be increased by:1. increasing the number of turns, 2. inserting a ferrite core of very high permeability with loop antenna’ scircumference which will rise the magnetic field intensity called ferrite loop.4.What are the types of loop antennas?

Loop antennas are classified into:1. Triangular2.square3.Circular4.Rectangular5.What are Electrically Small loop antennas?

Electrically Small loop antennas is one in which the overall length of the loop is less than one-tenth of the wavelength. Electrically Small loop antennas have small radiation resistances that are usually smaller than their loop resistances.They are very poor radiators and seldom employed for transmission in radio communication.6.What are Electrically large loop antennas?

Electrically Large loop antennas is one in which the overall length of the loop approaches the wavelength.7.List out the uses of loop antenna

Various uses of loop antenna are:*It is used as receiving antenna in portable radio and pagers*It is used as probes for field measurements and as directional antennas for radio wave navigation, *It is used to estimate the direction of radio wave propagation8.What are the parameters to be considered for the design of an helical antenna?

The parameters to be considered for the design of an helical antenna are:1. Bandwidth 2. Gain 3. Impedance 4. Axial Ratio

9.What are the types of radiation modes of operation for an helical antennaThe two types of radiation modes of operation possible for an helical antenna are:

1. Normal mode of operation 2. Axial mode of operation10.Which antenna will produce circularly polarized waves Helical antenna radiates circularly polarized wave.11.List the applications of helical antenna

The applications of helical antenna are:i.It became thw workhouse of space communications for telephone,television anddata,being employed both on satellites and at ground stationsii.Many satellites including weather satellites,data relay satellites all have helicalantennasiii.It is on many othe probes of planets and comets,including moon and mars,being usedalone,in arrays or as feeds for parabolic reflectors,its circular polarization and highgain and simplicity making it effective for space application12.What is the type of radiation pattern produced when a wave travels in a wire and draw its pattern. #Radiation pattern-Unidirectional pattern.


13.Why are some antennas called log periodic?When plotted on a lograthmic scale,the frequencies are equally spaced with aperiod equal to

logarithm of τ .ie.the structure repeats periodically with the logarithm of the frequency.hence the name periodic antenna.14.What are the requirements for a successful frequency independent operation.

i.An excitation of the antenna from the high frequencyii.Radiation in the forward direction must be zero.iii.Transmissions region should have proper characteristics impedence and negligible radiation.iv.For broad side radiation,phasings must be zero.v.Reflection region should be beyond the action region.

15.Write the advantages of log periodic antenna.i.No power is wasted in terminating impedenceii.Used for television reception

iii.This antenna will cover all higher frequencies bandiv.Low cost installation

16.What are resonant antenna?#The length of a resonant antenna is in exact multiples of χ/2.Resonant antennas are open at both

ends,They are not terminated by any resistance.They are used at fixed frequencies.Radiation patterns are multi directional.Hence resonant antennas are also known as periodic antennas.17.Differentiate V antenna from rhombic antenna

V antenna Rhombic antennaIt produces bidirectional lobes It produces uni directional lobesIt requires less space It requires more space for installationIt is fed by tuned feeder It is tuned,useful wideband antennaPower is wasted Power is usedIt is suitable for HF communication It is suitable F layer propagation

18..Draw the structure of 3 element Yagi uda antenna and give dimensioins and spacing between elements in terms of wavelength(M-07)

16 MARKS1.Write about helical antenna with its pitch angle and its applications2. Discuss the construction and principle of operation of rhombic antenna(A-99,2000)3.Write detailed notes on Log periodic antennas(A-99,2000)4.Witha asuitable diagram explain the construction and principle of operation of log periodic antenna (N-98,A-97)5.Explain the salient features of rhombic and yagi uda antenna(A-2000)6.How is analysis of LPDA done? (M-07)7.Design a LPDA and derive the parameters that describe the configuration of PLDA. (M-07,D-07)8.Name and draw frequency independent antenna. (M-05)9.What are various types of rhombic antenna. (M-07)10.Explain the structure of rhombic antenna and its radiation pattern.How rhombic antenna is designed in alignment design and maximum E design. (M-07,D-07)11.Explain the principle of operation and applications of parabolic reflector. (D-07)12.Write short notes on horn antenna.13..Explain about the reflector type of antennas.

UNIT-IVWAVE PROPAGATION

TWO MARKS1. Define Sky wave.

Waves that arrive at the receiver after reflection in the ionosphere is called sky wave.2.Define Tropospheric wave.

Waves that arrive at the receiver after reflection from the troposphere region is called Tropospheric wave .(ie 10 Km from Earth surface).3. Define Ground wave.

Waves propagated over other paths near the earth surface is called ground wave propagation.4.What are the type of Ground wave.

Ground wave classified into two types. i. Space wave, ii. Surface wave.


5. What is meant by Space Wave?It is made up of direct wave and ground reflected wave. Also includes the portion of energy

received as a result of diffraction around the earth surface and the reflection from the upper atmosphere.6. What is meant by Surface Wave?Wave that is guided along the earth’ s surface like an EM wave is guided by a transmission is called surface wave. Attenuation of this wave is directly affected by the constant of earth along which it travels.7. What is meant by fading?

Variation of signal strength occur on line of sight paths as a result of the atmospheric conditions and it is called .It can not be predicted properly.8. What are the type of fading?

Two types. i. Inverse bending. iii. Multi path fading.9. What is inverse and multi path fading.?

Inverse bending may transform line of sight path into an obstructed one.Multi path fading is caused by interference between the direct and ground reflected waves as well asinterference between two are more paths in the atmosphere.10.What is meant by diversity reception?

To minimize the fading and to avoid the multi path interference the technique used are diversityreception. It is obtained by two ways. i. Space diversity reception. ii. Frequency diversity reception.iii. Polarization diversity. 11. Define Space diversity Reception.

This method exploits the fact that signals received at different locations do not fade together. It and the antenna which high signal strength at the moment dominates.12 .Define frequency diversity Reception.

his method takes advantage of the fact that signals of slightly different frequencies do not fadesynchronously. This fact is utilized to minimize fading in radio telegraph circuits.13. Define polarization diversity reception.

It is used in normally in microwave links, and it is found that signal transmitted over the same path in two polarizations have independent fading patterns.in broad band dish antenna system, Polarization diversity combined with frequency diversity reception achieve excellent results.14. What is meant by Faraday’ s rotation.?

Due to the earth’ s magnetic fields, the ionosheric medium becomes anisotropic and the incidentplane wave entering the ionosphere will split into ordinary and extra ordinary waves/modes.When these modes re-emerge from the ionosphere they recombine into a single plane wave again.Finally the plane of polarization will usually have changed, this phenomenon is known as Faraday’ srotation.15. What are the factors that affect the propagation of radio waves.?i. Curvature of earth. ii. Earth’ s magnetic field. iii. Frequency of the signal. iv. Plane earth reflection.16. Define gyro frequency.

Frequency whose period is equal to the period of an electron in its orbit under the influence of theearths magnetic flux density B.17. Define critical frequency.For any layer , the highest frequency that will be reflected back for vertical incidence is fcr = 9¥1max18. Define Magneto-Ions Splitting.

The phenomenon of splitting the wave into two different components (ordinary and extra-ordinary) by the earths magnetic field is called Magneto-Ions Splitting.19.Define LUHF.

The lowest useful HF for a given distance and transmitter power is defined as the lowest frequency that will give satisfactory reception for that distance and power. It depends oni. The effective radiated power ii. Absorption character of ionosphere for the paths between transmitter and receiver. iii. The required field strength which in turn depends upon the radio noise at the receiving location and type of service involved .20. Define Refractive index.

It is defined as n = c / vp Velocity of light in vacua n = Phase velocity in the medium n = ¥ r


21.Define maximum Usable Frequency.(MUF)The maximum Frequency that can be reflected back for a given distance of transmission is called

the maximum usable frequency (MUF) for that distance.MUF = fcr_VHF_ i22. Define skip distance.

The distance with in which a signal of given frequency fails to be reflected back is the skipdistance for that frequency.The higher the frequency the greater the skip distance.23. Define Optimum frequency?

Otimum frequency for transmitting between any two points is therefore selected as some frequency lying between about 50 and 85 percent of the predicted maximum usable frequency between those points.24. What is wave impedance.?25. Define wave velocity and Group velocity?wave velocity Group velocity,26.Explain the phenomenon of duct propagation.(D-07)

Due to the presence of moisture,the electromagnetic rays are curved along the earth’s surfece,having the same curvature as that of earth.Under such conditions,wave tends to get trapped or guided along a duct propagation making the atmosphere to bahave as a leaky waveguide.with the duct,it is possible for line of communication to stretch much beyond the line of sight,sometimes upto 640kms.This is known as duct propagation.27.What is the significance of faraday rotation?(N-06)

i)The rotation of the plane of polarization ii)At high frequencies,the amount of rotation is much smaller.iii)The rotation angle will lead to a loss in received signal power at the receiving antenna because of the resultant polarization mizmatch.

16 MARKS1.Write Explanatory notes on (D-07)a)critical frequency,b)Tropospheric propagation,c)Ground wave propagation2.Explain the mechanism of ionospheric propagation(D-07,A-05)3.Derive the expression for refractive index of ionosphere and critical frequency. (M-07)4.Explain ground wave propagation and obtain expression for field strength(N-07)5.Show the radius of curvature of wave path is function of rate of change of dielectric constant or refractive index with height in space wave propagation. (D-07)6.Explain the characteristics of different ionized regions of ionosphere,drawing the structure above the earth. (N-07)7.Derive the expression for refractive index of the ionosphere. (D-07) 8.Derive the expression for calculating field strength at adistance in space wave propagation. (M-07)9.Explain the advantages of tropospheric wave propagation and sky wave propagation. (D-05)10.Describe the need for diversity reception and typical schemes.11.Obtain the expression for the field strength of space wave signal. (A-2000,M-07)

UNIT VANTENNA & IONOSPHERE MEASUREMENTS

1. What is meant by reciprocity Theorem.?Ans:If an e.m.f is applied to the terminals of an antenna no.1 and the current measured at the

terminals of the another antenna no.2, then an equal current both in amplitude and phase will be obtained at the terminal ofthe antenna no.1 if the same emf is applied to the terminals of antenna no.2.2.What are the parameters that can be measure using antenna? The parameters are directional pattern,gain,phase,polarization,impedance,efficiency.3.What do you mean by near field and far field of an antenna? In antenna field near to the radiator is the near field or Fresnel zoneand at large distance as far field or Fraunhoffer zone.R=2L2 /λ4.What are the possible errors in antenna measurements? The possible errors in antenna measurements are phase error,amplitude error,reflections,Man made error,Atmospheric abnormalities,Impedance mismatch,Incorrect use of cables,


5.What are the types of measurement ranges? The types are Elevated ranges,ground reflection ranges,Anechoic chamber,Compact antenna test ranges.Near field ranges,6.what are the methods to measure gain of an antenna? 1.Absolute method2.Comparision method3.Radar Techniques.7.what is meant by vertical incidence?8.Define group velocity and group delay/9. what are the methods to measure Phase of an antenna? 1.Direct method,2.reference antenna method 3.Differntial method.10. what are the methods to measure Efficiency of an antenna?1.Directivity/Gain method2.Radiometric method,3.Random field method4.Wheeler cap method.11.Write down the relation between the oblique and vertical incidence in transmission.

16 MARKS1.Explain in detail about antenna mesurements.2.write short notes on near field and far field measurements.3.Explain in detail about antenna impedance measurement.4.Explain in detail about antenna parameters measurement.5.Elaborately explain about ionospheric measurements.6.Dicuss antenna measurement ranges along with its types in detail.


antenna & wave propagation

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