Antenna and wave propagationTwo marks

Question and answers

1) What is magnetic vector potential?The source for magnetic vector potential is current element. The current having both magnitude and direction. Hence the potential in the case of magnetic field is magnetic vector potential.The expressions for magnetic vector potential (A) A = μ/401 J/r dV (volts /metre)2) What is a monopole antenna?A monopole antenna consists of one half of a dipole (usually a short vertical) antenna mounted above the earth or group (reflecting plane).3) What is a quarter wave monopole?One-quarter wavelength long .it is also called as Marconi antenna.4) What is a hertz antenna?Effective length or height of the antenna becomes half of the actual length.5) Define electric scalar potential.The source for producing a electric potential is charge. The charge is having magnitude only. Hence the potential in the case of electric charge is electric scalar potential.E= -V Unit is weber/m²6) Write down the expressions for magnetic vector potential using threestandard current distributions.i) for volume currentA = μ/40 1 J/r dV (volts /metre)ii) for line currentA = μ/40 1 I/r dl (volts /metre)iii) for surfaceA = μ/40 1 K/r dS (volts /metre)7) What is retarded current?Since current flowing through a short dipole is assumed to be constant throughout its length, the effect of this current is not felt instantaneously at a distant point P, but only after an interval equal to the time required for the wave to propagate over a distance r. This current is called as retarded current.Expressions for retarded current[I] = Im e jw(t- r/c) : r/c – retardation current.8) Define hertzian dipole?Hertzian dipole is defined as a short linear conductor or short electric dipole, whose length is very short compared to wavelength (l <) current is assumed to be constant throughout its length.9) Write down the expressions for radiated fields of a half wave dipole antenna (/2) .E I =60 Im /r [( cos(0/2 cosI)/sinI]H , = Im /20r [( cos(0/2 cosI)/sinI]10. State reciprocity principle.If a current I1 at the terminals of antenna no.1 induces an emf E21 at the open terminals of antenna no.2 and a current I2 at the terminals of antenna no.2 induces an emf E12 at the open terminals of antenna no.1 then E12= E21provided I1= I211. Define antenna .An antenna is a structure that has been designed to radiate or receive electromagnetic waves.12. Define Radiation patternAn antenna radiation pattern is defined as a mathematical function or a graphical representation of the

radiation properties of the antennas a function of space coordinates. The radiation properties include power flux density, radiation intensity, field strength, directivity, phase or polarization.13). What are the two types of radiation pattern.Field patternIf the radiation from the antenna is expressed in terms of the fieldstrength(either E or H ) then the radiation pattern is called as field pattern.Power patternIf the radiation from the antenna is expressed in terms of power per unitarea, then the resultant pattern is power pattern.14) Define Induction field(near field)The field which predominates at the points closer to the current element where r is small is known as induction field. The near field is inversely proportional to square of the distance(1/ r²).15) Write down expression for retarded vector potential.Retarded vector potential [A] = μ/40 1v ( Jm e jw(t- r/c) ) / r.16) Write down the expression for radiation resistance of a hertzian dipoleRadiation resistance Rr = 80 0² ( L / G)² ohms17) Define retardation timeIt is the time required for the wave to propagate over the distance r. It is given by r/c where c is 3*108m/s.18) What is the radiation resistance of a current element whose overall length is G/50.Radiation resistance Rr = 80 0² ( L / G)² ohmsGiven L = G /50.Ans = 0.316 ohms19) Calculate the physical height of a halfwave dipole (G/2) having antenna Q of 30 and bandwidth of 10 MHz.f = Q. BWG= c / f ; ans: 0.5 m20) Calculate the bandwidth of a 50 cm long half wave diploe having a Q of 15.Bandwidth = f / Q;Height of a half wave dipole (G/2) = 50 cm.f = C/ Gans : 20 MHz.21) If the electric field strength(E) of a plane wave is 5 volts/metre. Calculate the strength of a magnetic field(H)in free space.E I = 5 vR = 120 0 = E I / H S22). What is the Special feature of folded dipole antennas?Folded dipole has got a versatile quality of providing any desired input impedance by increasing the number of elements and selecting suitable lengths of dipole.23). What are the Advantages of folded dipole? AN.U.2003The radiation pattern of a folded dipole and a conventional half waveis same but the input impedance of the folded dipole is higher. It has low directivity and bandwidth than simple dipole.24). What is Application of folded dipole?Folded dipole is used as a driven element in yagi-uda antenna. It has built in impedance transforming properties, which makes it easier to match a transmission line that feeds the antenna . Unit.ii1.What is a Loop antenna? The 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 likes rectangular, square, triangular, hexagonal and circular

loop, most popular out of these are square and circle.2.What are the Applications of loop antenna?1.They are seldom employed for transmission in radio communicating they are used in such application; it is usually in receiving mode where antenna efficiency is not important2.They also use it for finding the direction.3. What is meant by Broadband antenna?Antenna which maintain certain required characteristics like gain, front to back ratio, SWR, polarization, input impedance and radiation pattern over wide range of frequencies are called wide band or broad band antenna. EG: Log-periodic5. What is the Special feature of folded dipole antennas?Folded dipole has got a versatile quality of providing any desired input impedance by increasing the number of elements and selecting suitable lengths of dipole.6. What are the Advantages of folded dipole? The radiation pattern of a folded dipole and a conventional half wave is same but the input impedance of the folded dipole is higher. It has low directivity and bandwidth than simple dipole.7. What is Application of folded dipole?Folded dipole is used as a driven element in yagi-uda antenna. It has built in impedance transforming properties, which makes it easier to match atransmission line that feeds the antenna.8. What are the disadvantages of loop antenna?Only suitable for LF & MF except for a very small distance. Transmission efficiency is poor & hence cannot be used for UHF unless design is changed. Spurious induced voltages are produced, if nearby loop, wires & conductors are present. It is subjected to antenna effect & night effect, which are minimizedby balancing & using Adcock antenna for direction finding.

9. What is Adcock antenna? & how it eliminates the effects of loop antenna?It consists of 2 spaced vertical antenna. In vertical polarization the action is same as loop antenna. The horizontally polarized down coming sky waves have no effect on this antenna due to its circuit arrangement. If the horizontal wires are placed inside a metal tube shielded from the radiowaves, this antenna system becomes insensitive to horizontally polarize down coming sky waves & thus it is free from polarization effect.10. compare half wave dipole & folded dipole? Half wave dipole Folded dipole1. Directivity is unidirectional Directivity is bi-directional, butbecause of the distribution ofcurrents in the parts of foldeddipole, the input impendence ishigher.Used as impedance matchingdevices.2 Broadness in bandwidth is lessthan folded dipole.Broadness in bandwidth11.What is a normal mode of helix antenna?Radiation field is maximum in the direction normal to the helix axis &wave is nearly or exactly circularly polarized wave . Mode is said to benormal if the dimensions of helix is small compared with the wavelength.12. What is a axial mode of helix antenna?Radiation field is maximum in the end fire direction.(ie) along the

helix axis & polarization is circular or nearly circular.13. How bandwidth & efficiency is increased?

Efficiency is increased by increasing the dimension & current feed inphase with helix axis.Bandwidth is increased by providing phase shifter at regular intervals.14.How the axial mode is improved?When the helix circumference D & spacing S of order of onewavelegth. Axial mode of radiation is produced by raising helixcircunference (c/G) of order of one wavelength & spacing is approximatelyof G/a.15.Define radiation efficiencyRadiation efficiency=Max power gain/directivity16.What is the error introduced in direction finding of loop antenna?Antenna or Vertical effectNight effect or Aeroplane effect or polarization error.17. What is the radiation resistance of multi turn loop antenna? & how itchange the o/p power?Rr = 31,200 (NA/ G 2 ) 2 N= number of turns , G= wavelength, A=effective area.18. What is the principle of pattern multiplication?In case of isotropic antenna arrays the total field of the antenna arrayis simply the vector sum of those of individual radiating sources.In case of non isotropic, but similar sources I s the multiplication ofthe individual source patterns and the pattern of an array of isotropic pointsources, each located at the phase centre of individual sources and havingrelative amplitude and phase. Whereas the total phase pattern is theaddition of the phase patterns of the individual sources and tat of the arrayof isotropic point sources19. What is the general effect of earth on antennas?Effect of earth modifies the following:1.Currents flowing in reflecting surface.2.Radiation pattern.20. What is an “array factor”?It is apparent that the total field of an array is equal to equal field of asingle element positioned at the origin multiplied by a factor which is widelyreferred as array factor.21. What are the disadvantages of binomial arrays?1. As HPBW increases and hence directivity decreases.2. For design of a large array, larger amp ratio of sources is required.22. What is the disadvantage of a binomial array?A major practical disadvantage of binomial array is the widevariations between the amplitudes of the different elements of an array,especially for an array with a large no of elements. This leads to very lowefficiencies, and makes this method not very desirable in practice.23. What is a binomial array?The coefficients of binomial expansion represent relative amplitudesof the elements. Since the coefficients are determined from the binomialseries, expansion the array is known as binomial array.

24. What are the types of antenna arrays?1.Broad side array2.End fire array3.Collinear array4.Parasitic array25. Define the length of an arrayThe length of an array is the length measured along the axis of thearray from the first element to the last element.26. What is array factor or space factor?The factor by which the antenna array increases the field strength overthat of a single element radiating the same total power is called array factoror space factor.27. Define antenna array. AN.U.2003Antenna array is an arrangement of several individual antennas sospaced and phased that their individual electric field contributions combinein one preferred direction and cancel in all other directions to get greaterdirectivity.28. How to convert broad side array radiation pattern into unidirectional?AN.U.2004Bidirectional pattern of a broad side array can be converted intounidirectional by installing an indentical array behind this array at a distanceG/4 and exciting it by current leading in phase by 90*.29. What are the applications of arrays?Because of their physical size, their use is generally limited to HFbands and higher but they are used in LF bands for point to pointcommunications. They are also used in overseas broadcasting stations inMF and HF bands for repeated broad casting to some distant area.30.Give the formula for beam width between first nulls(BWFN) of a broadside array.BWFN=115/(L/G)L=length of arrayG=wave length31.Give the formula for BWFN of an end-fire array.BWFN=115/X(L/G)32.Give the formula for half power beam width of a broad side array.BWFN=51/(L/G)L=length of arrayG=wave length.33.Give the formula for HPBW of an end-fire array.HPBW=52/X(L/G)34.Give the formula for calculating directive gain of broad side array.Directive gain=2L/G(when the elements along with axis parallel toarray axis)Directive gain=4L/G(when the elements at right angles to array axis)35.What is the formula for directive gain when the elements right angels toarray axis?Directive gain=4L/G36. What is a collinear array? AN.U.2004In this array the antennas are arranged co-axially and the elements are

fed with equal inphase currents. The radiation pattern of a collinear arrayhas circularly symmetry with its main lobe every where perpendicular to theprinciple axis.37. When will be the gain of the collinear array be maximum?When the spacing between elements is of the order of 0.3G to 0.5G.38. Define antenna .An antenna is a structure that has been designed to radiate or receiveelectromagnetic waves.39. Define Radiation patternAn antenna radiation pattern is defined as a mathematical function ora graphical representation of the radiation properties of the antennas afunction of space coordinates.The radiation properties include power flux density, radiation intensity, fieldstrength,directivity, phase or polarization.40. What are the two types of radiation pattern.1) Field patternIf the radiation from the antenna is expressed in terms of the fieldstrength(either E or H ) then the radiation pattern is called as fieldpattern.2) Power patternIf the radiation from the antenna is expressed in terms of power perunit area, then the resultant pattern is power pattern.41. What is broadside array?The simplest array consist of a number of dipoles of equal size,equallyspaced along a straight line with the dipole fed in the same phase from thesame sources. Such an arrangement is called broad side array.42.What is an end-fire array?In the end-fire array each element is fed with same magnitude butdifferent phase and this phase is progressive from left to right.43.What is the direction of maximum radiation is maximum only in onedirection that is in the direction of array axis.(180 & 360 (or) 0 degree)44.What are the characteristics of an end-fire array and broad side array?1.linear 2.Resonant 3.Narrow bandwidth45.What is a collinear array? AN.U.2004In this array the antennas are arranged co-axially and the elements arefed with equal inphase currents. The radiation pattern of a collinear arrayhas circularly symmetry with its main lobe every where perpendicular to theprinciple axis.46. When will be the gain of the collinear array be maximum?When the spacing between elements is of the order of 0.3G to 0.4G1) What is magnetic vector potential?The source for magnetic vector potential is current element. Thecurrent having both magnitude and direction. Hence the potential in the caseof magnetic field is magnetic vector potential.The expressions for magnetic vector potential (A)A = μ/401 J/r dV (volts /metre)2) What is a monopole antenna?A monopole antenna consists of one half of a dipole (usually a shortvertical) antenna mounted above the earth or group (reflecting plane).

3) What is a quarter wave monopole?One-quarter wavelength long .it is also called as Marconi antenna.4) What is a hertz antenna?Effective length or height of the antenna becomes half of the actuallength.5) Define electric scalar potential.The source for producing a electric potential is charge. The charge ishaving magnitude only. Hence the potential in the case of electric charge iselectric scalar potential.E= -;VUnit is weber/m²6) Write down the expressions for magnetic vector potential using threestandard current distributions.i) for volume currentA = μ/40 1 J/r dV (volts /metre)ii) for line currentA = μ/40 1 I/r dl (volts /metre)iii) for surfaceA = μ/40 1 K/r dS (volts /metre)7) What is retarded current?Since current flowing through a short dipole is assumed to be constantthroughout its length, the effect of this current is not felt instantaneously at aDistant point P, but only after an interval equal to the time required for thewave to propagate over a distance r. This current is called as retardedcurrent.Expressions for retarded current[I] = Im e jw(t- r/c) : r/c – retardation current.8) Define hertzian dipole?Hertzian dipole is defined as a short linear conductor or short electricdipole , whose length is very short compared to wavelength(l <current is assumed to be constant throughout its length.9) Write down the expressions for radiated fields of a half wave dipoleantenna(G/2) .E I =60 Im /r [( cos(0/2 cosI)/sinI]H , = Im /20r [( cos(0/2 cosI)/sinI]10. State reciprocity principle.If a current I1 at the terminals of antenna no.1 induces an emf E21 at theopen terminals of antenna no.2 and a current I2 at the terminals of antennano.2 induces an emf E12 at the open terminals of antenna no.1 then E12= E21provided I1= I211. Define antenna .An antenna is a structure that has been designed to radiate or receiveelectromagnetic waves.12. Define Radiation patternAn antenna radiation pattern is defined as a mathematical function or agraphical representation of the radiation properties of the antennas afunction of space coordinates.The radiation properties include power flux density, radiation intensity, fieldstrength,directivity, phase or polarization.

13). What are the two types of radiation pattern.Field patternIf the radiation from the antenna is expressed in terms of the fieldstrength(either E or H ) then the radiation pattern is called as field pattern.Power patternIf the radiation from the antenna is expressed in terms of power per unitarea, then the resultant pattern is power pattern.14) Define Induction field(near field)The field which predominates at the points closer to the current elementwhere r is small is known as induction field. The near field is inverselyproportional to square of the distance(1/ r²).15) Write down expression for retarded vector potential.Retarded vector potential [A] = μ/40 1v ( Jm e jw(t- r/c) ) / r.16) Write down the expression for radiation resistance of a hertzian dipoleRadiation resistance Rr = 80 0² ( L / G)² ohms17) Define retardation timeIt is the time required for the wave to propagate over the distance r. It isgiven by r/c where c is 3*108 m/s.18) What is the radiation resistance of a current element whose overalllength is G/50.Radiation resistance Rr = 80 0² ( L / G)² ohmsGiven L = G /50.Ans = 0.316 ohms19) Calculate the physical height of a halfwave dipole (G/2) havingantenna Q of 30 and bandwidth of 10 MHz.f = Q. BWG= c / f ; ans: 0.5 m20) Calculate the bandwidth of a 50 cm long half wave diploe having a Q of15.Bandwidth = f / Q;Height of a half wave dipole (G/2) = 50 cm.f = C/ Gans : 20 MHz.21) If the electric field strength(E) of a plane wave is 5volts/metre,calculate the strength of a magnetic field(H)in free space.E I = 5 vR = 120 0 = E I / H S22). What is the Special feature of folded dipole antennas?Folded dipole has got a versatile quality of providing any desired inputimpedance by increasing the number of elements and selecting suitablelengths of dipole.23). What are the Advantages of folded dipole? AN.U.2003The radiation pattern of a folded dipole and a conventional half waveis same but the input impedance of the folded dipole is higher. It has lowdirectivity and bandwidth than simple dipole.24). What is Application of folded dipole?Folded dipole is used as a driven element in yagi-uda antenna. It hasbuilt in impedance transforming properties, which makes it easier to match atransmission line that feeds the antenna .

Unit.ii1.What is a Loop antenna? AN.U.2003The loop antenna is a radiating coil of any convenient cross section ofone or more turns, carrying radio frequency current. It may assume anyshape likes rectangular, square, triangular, hexagonal and circular loop, mostpopular out of these are square and circle.2.What are the Applications of loop antenna?1.They are seldom employed for transmission in radio communicatingthey are used in such application; it is usually in receiving mode whereantenna efficiency is not important2.They also use it for finding the direction.3. What is meant by Broadband antenna?Antenna which maintain certain required characteristics like gain,front to back ratio, SWR, polarization, input impedance and radiation patternover wide range of frequencies are called wide band or broad band antenna.EG: Log-periodic5. What is the Special feature of folded dipole antennas?Folded dipole has got a versatile quality of providing any desiredinput impedance by increasing the number of elements and selecting suitablelengths of dipole.6. What are the Advantages of folded dipole? AN.U.2003The radiation pattern of a folded dipole and a conventional half waveis same but the input impedance of the folded dipole is higher. It has lowdirectivity and bandwidth than simple dipole.7. What is Application of folded dipole?Folded dipole is used as a driven element in yagi-uda antenna. It hasbuilt in impedance transforming properties, which makes it easier to match atransmission line that feeds the antenna.8. What are the disadvantages of loop antenna?

Only suitable for LF & MF except for a very small distance.Transmission efficiency is poor & hence cannot be used for UHFunlessdesign is changed.Spurious induced voltages are produced, if nearby loop, wires &conductors are present.It is subjected to antenna effect & night effect, which are minimizedby balancing & using Adcock antenna for direction finding.

9. What is Adcock antenna? & how it eliminates the effects of loop antenna?AN.U.2003It consists of 2 spaced vertical antenna.In vertical polarization theaction is same as loop antenna. The horizontally polarized down coming skywaves have no effect on this antenna due to its circuit arrangement. If thehorizontal wires are placed inside a metal tube shielded from the radiowaves, this antenna system becomes insensitive to horizontally polarizedown coming sky waves & thus it is free from polarization effect.10. compare half wave dipole & folded dipole? AN.U.2005s.no Half wave dipole Folded dipole

1. Directivity is unidirectional Directivity is bi-directional, butbecause of the distribution ofcurrents in the parts of foldeddipole, the input impendence ishigher.Used as impedance matchingdevices.2 Broadness in bandwidth is lessthan folded dipole.Broadness in bandwidth11.What is a normal mode of helix antenna?Radiation field is maximum in the direction normal to the helix axis &wave is nearly or exactly circularly polarized wave . Mode is said to benormal if the dimensions of helix is small compared with the wavelength.12. What is a axial mode of helix antenna?Radiation field is maximum in the end fire direction.(ie) along thehelix axis & polarization is circular or nearly circular.13. How bandwidth & efficiency is increased? Efficiency is increased by increasing the dimension & current feed inphase with helix axis.Bandwidth is increased by providing phase shifter at regular intervals.14.How the axial mode is improved?When the helix circumference D & spacing S of order of onewavelegth. Axial mode of radiation is produced by raising helixcircunference (c/G) of order of one wavelength & spacing is approximatelyof G/a.15.Define radiation efficiencyRadiation efficiency=Max power gain/directivity16.What is the error introduced in direction finding of loop antenna?Antenna or Vertical effectNight effect or Aeroplane effect or polarization error.17. What is the radiation resistance of multi turn loop antenna? & how itchange the o/p power?Rr = 31,200 (NA/ G 2 ) 2 N= number of turns , G= wavelength, A=effective area.18. What is the principle of pattern multiplication?In case of isotropic antenna arrays the total field of the antenna arrayis simply the vector sum of those of individual radiating sources.In case of non isotropic, but similar sources I s the multiplication ofthe individual source patterns and the pattern of an array of isotropic pointsources, each located at the phase centre of individual sources and havingrelative amplitude and phase. Whereas the total phase pattern is theaddition of the phase patterns of the individual sources and tat of the arrayof isotropic point sources19. What is the general effect of earth on antennas?Effect of earth modifies the following:1.Currents flowing in reflecting surface.2.Radiation pattern.20. What is an “array factor”?

It is apparent that the total field of an array is equal to equal field of asingle element positioned at the origin multiplied by a factor which is widelyreferred as array factor.21. What are the disadvantages of binomial arrays?1. As HPBW increases and hence directivity decreases.2. For design of a large array, larger amp ratio of sources is required.22. What is the disadvantage of a binomial array?A major practical disadvantage of binomial array is the widevariations between the amplitudes of the different elements of an array,especially for an array with a large no of elements. This leads to very lowefficiencies, and makes this method not very desirable in practice.23. What is a binomial array?The coefficients of binomial expansion represent relative amplitudesof the elements. Since the coefficients are determined from the binomialseries, expansion the array is known as binomial array.24. What are the types of antenna arrays?1.Broad side array2.End fire array3.Collinear array4.Parasitic array25. Define the length of an arrayThe length of an array is the length measured along the axis of thearray from the first element to the last element.26. What is array factor or space factor?The factor by which the antenna array increases the field strength overthat of a single element radiating the same total power is called array factoror space factor.27. Define antenna array. AN.U.2003Antenna array is an arrangement of several individual antennas sospaced and phased that their individual electric field contributions combinein one preferred direction and cancel in all other directions to get greaterdirectivity.28. How to convert broad side array radiation pattern into unidirectional?AN.U.2004Bidirectional pattern of a broad side array can be converted intounidirectional by installing an indentical array behind this array at a distanceG/4 and exciting it by current leading in phase by 90*.29. What are the applications of arrays?Because of their physical size, their use is generally limited to HFbands and higher but they are used in LF bands for point to pointcommunications. They are also used in overseas broadcasting stations inMF and HF bands for repeated broad casting to some distant area.30.Give the formula for beam width between first nulls(BWFN) of a broadside array.BWFN=115/(L/G)L=length of arrayG=wave length31.Give the formula for BWFN of an end-fire array.BWFN=115/X(L/G)

32.Give the formula for half power beam width of a broad side array.BWFN=51/(L/G)L=length of arrayG=wave length.33.Give the formula for HPBW of an end-fire array.HPBW=52/X(L/G)34.Give the formula for calculating directive gain of broad side array.Directive gain=2L/G(when the elements along with axis parallel toarray axis)Directive gain=4L/G(when the elements at right angles to array axis)35.What is the formula for directive gain when the elements right angels toarray axis?Directive gain=4L/G36. What is a collinear array? AN.U.2004In this array the antennas are arranged co-axially and the elements arefed with equal inphase currents. The radiation pattern of a collinear arrayhas circularly symmetry with its main lobe every where perpendicular to theprinciple axis.37. When will be the gain of the collinear array be maximum?When the spacing between elements is of the order of 0.3G to 0.5G.38. Define antenna .An antenna is a structure that has been designed to radiate or receiveelectromagnetic waves.39. Define Radiation patternAn antenna radiation pattern is defined as a mathematical function ora graphical representation of the radiation properties of the antennas afunction of space coordinates.The radiation properties include power flux density, radiation intensity, fieldstrength,directivity, phase or polarization.40. What are the two types of radiation pattern.1) Field patternIf the radiation from the antenna is expressed in terms of the fieldstrength(either E or H ) then the radiation pattern is called as fieldpattern.2) Power patternIf the radiation from the antenna is expressed in terms of power perunit area, then the resultant pattern is power pattern.41. What is broadside array?The simplest array consist of a number of dipoles of equal size,equallyspaced along a straight line with the dipole fed in the same phase from thesame sources. Such an arrangement is called broad side array.42.What is an end-fire array?In the end-fire array each element is fed with same magnitude butdifferent phase and this phase is progressive from left to right.43.What is the direction of maximum radiation is maximum only in onedirection that is in the direction of array axis.(180 & 360 (or) 0 degree)44.What are the characteristics of an end-fire array and broad side array?1.linear 2.Resonant 3.Narrow bandwidth

45.What is a collinear array? AN.U.2004In this array the antennas are arranged co-axially and the elements arefed with equal inphase currents. The radiation pattern of a collinear arrayhas circularly symmetry with its main lobe every where perpendicular to theprinciple axis.46. When will be the gain of the collinear array be maximum?When the spacing between elements is of the order of 0.3G to 0.4G