Question 1. Define An Antenna?
Antenna is a transition device or a transducer among a guided wave and a unfastened area wave or vice-versa. Antenna is also stated to be an impedance remodeling device.
Question 2. What Is Meant By Radiation Pattern?
Radiation pattern is the relative distribution of radiated power as a feature of distance in space .It is a graph which shows the version in actual area electricity of the EM wave in any respect points which are at same distance from the antenna. The strength radiated in a particular course by means of an antenna is measured in terms of FIELD STRENGTH. (E Volts/m)
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Question three. Define Radiation Intensity?
The electricity radiated from an antenna in keeping with unit solid angle is called the radiation intensity U (watts consistent with steradian or in keeping with square degree). The radiation depth is impartial of distance.
Question 4. Define Beam Efficiency?
The total beam vicinity (WA) includes the main beam place (WM) plus the minor lobe area (Wm).
Thus WA = WM+ Wm.
The ratio of the primary beam location to the entire beam vicinity is called beam performance.
Beam performance (SM) = WM / WA.
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Question five. Define Directivity?
The directivity of an antenna is identical to the ratio of the maximum energy density P (q,f)max to its average price over a sphere as found in the some distance discipline of an antenna.
D = P (q,f)max / P(q,f)av. Directivity from Pattern.
D = 4p / WA. Directivity from beam area (WA).
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Question 6. What Are The Different Types Of Aperture?
Question 7. Define Different Types Of Aperture?
Effective aperture (Ae): It is the location over which the energy is extracted from the incident wave and brought to the load is referred to as 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 electricity as heat.
Collecting aperture (Ae): It is the addition of above three apertures.
Physical aperture (Ap): This aperture is a measure of the bodily length of the antenna.
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Question 8. Define Aperture Efficiency?
The ratio of the powerful aperture to the physical aperture is the aperture efficiency. I.E Aperture efficiency = hap = Ae / Ap (dimensionless).
Question nine. What Is Meant By Effective Height?
The effective peak h of an antenna is the parameter associated with the aperture. It can be described as the ratio of the caused voltage to the incident area.I.E H= V / E.
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Question 10. What Are The Field Zones?
The fields around an antenna can be divided into two primary areas.
Near area quarter (Fresnel area)
Far field sector (Fraunhofer quarter)
Question eleven. What Is Meant By Polarization?
The polarization of the radio wave may be defined via direction in which the electric vector E is aligned for the duration of the passage of atleast one full cycle.Also polarization can also be defined the bodily orientation of the radiated electromagnetic waves in area. The polarization are 3 kinds. They are Elliptical polarization ,circular polarization and linear polarization.
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Question 12. What Is Meant By Front To Back Ratio?
It is defined because the ratio of the power radiated in preferred path to the power radiated in the opposite direction. I.E FBR = Power radiated in preferred direction / energy radiated in the opposite course.
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Question 13. Define Antenna Efficiency?
The performance of an antenna is described as the ratio of strength radiated to the total enter electricity supplied to the antenna. Antenna efficiency = Power radiated / Total enter Power.
Question 14. What Is Radiation Resistance ?
The antenna is a radiating tool wherein power is radiated into area inside the shape of electromagnetic wave. W’ = I2 R Rr = W’/ I2 Where Rr is a fictitious resistance known as referred to as as radiation resistance.
Question 15. What Is Meant By Antenna Beam Width?
Antenna beamwidth is a measure of directivity of an antenna. Antenna beam width is an angular width in degrees, measured at the radiation sample (important lobe) among points where the radiated electricity has fallen to 1/2 its maximum price. This is known as as "beam width" among half strength points or half of energy beam width.(HPBW).
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Question sixteen. What Is Meant By Reciprocity Theorem?
If an e.M.F is carried out to the terminals of an antenna no.1 and the modern measured at the terminals of the any other antenna no.2, then an equal contemporary both in amplitude and phase could be received on the terminal of the antenna no.1 if the same emf is carried out to the terminals of antenna no.2.
Question 17. What Is Meant By Isotropic Radiator?
A isotropic radiator is a fictitious radiator and is described as a radiator which radiates fields uniformly in all directions. It is likewise known as as isotropic supply or omni directional radiator or actually unipole.
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Question 18. Define Gain?
The ratio of maximum radiation intensity in given direction to the most radiation depth from a reference antenna produced within the equal path with same input power. I.E Maximum radiation intensity from test antenna (G)= Maximum radiation intensity from the reference antenna with equal enter power.
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Question 19. Define Self Impedance?
Self impedance of an antenna is defined as its input impedance with all different antennas are absolutely eliminated i.E faraway from it.
Question 20. Define Mutual Impedance?
The presence of near by means of antenna no.2 induces a cutting-edge in the antenna no.1 indicates that presence of antenna no.2 modifications the impedance of the antenna no.1. This impact is known as mutual coupling and consequences in mutual impedance.
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Question 21. What Is Meant By Cross Field?
Normally the electrical discipline E is perpendicular to the path of wave propagation. In a few scenario the electric subject E is parallel to the wave propagation that circumstance is referred to as Cross discipline.
Question 22. Define Axial Ratio?
The ratio of the essential to the minor axes of the polarization ellipse is known as the Axial Ratio (AR).
Question 23. What Is Meant By Beam Area?
The beam region or beam solid attitude or WA of an antenna is given by the normalized energy pattern over a sphere.
WA = ò ò4p Pn ( q,f ) dW
Where dW = Sin q dq.Df
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Question 24. What Is Duality Of Antenna?
It is defined as an antenna is a circuit tool with a resistance and temperature on the one hand and the distance tool on the alternative with radiation styles, beamangle, directivity gain and aperture.
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Question 25. State Poynting Theorem?
It states that the vector fabricated from electric powered subject intensity vector E and the magnetic filed intensity vector H at any point is a degree of the fee of power flow per unit vicinity at that factor. The path of energy waft is perpendicular to both the electric field and magnetic subject additives.
Question 26. What Is Point Source?
It is the waves originate at a fictitious volume less emitter source at the center ‘O’ of the commentary circle.
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Question 27. What Is Meant By Array?
An antenna is a device of comparable antennas orientated similarly to get greater directivity in a favored route.
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Question 28. What Is Meant By Uniform Linear Array?
An array is linear when the factors of the array are spaced equally along the directly line. If the factors are fed with currents of equal significance and having a uniform innovative section shift along the line, then it's far referred to as uniform linear array.
Question 29. What Are The Types Of Array?
Broad facet array.
End fireplace array
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Question 30. What Is Broad Side Array?
Broad facet array is defined as an arrangement wherein the essential route of radiation is perpendicular to the array axis and additionally the plane containing the array element.
Question 31. Define End Fire Array?
End fire array is described as an association in which the major route of radiation is coincides with the array axis.
For give up fireplace array δ = - β d
wherein β = 2Π / λ and d = distance between the factors.
Question 32. What Is Collinear Array?
In this array the antenna elements are organized coaxially by way of mounting the factors end to end in directly line or stacking them one over the alternative with radiation sample round symmetry.
Eg. Omnidirectional antenna.
Question 33. What Is Parasitic Array?
In this array the elements are fed parasitically to reduce the trouble of feed line. The strength is given to at least one element from that other factors get by means of electro magnetic coupling.
Eg. Yagi uda antenna.
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Question 34. What Is The Condition On Phase For The End Fire Array With Increased Directivity?
When δ = - β d, produces most subject inside the direction φ = zero however dies no longer provide the maximum directivity. It has been proven by Hansen and woodyard that a big directivity is obtained by way of growing the phase trade among the resources in order that δ = - (βd + π / n ).
This condition may be known as the circumstance for increased directivity.
Question 35. Define Array Factor?
The normalized value of the entire field is given via,
E = ( 1 / n) ( sin (n Ψ / 2) / sin ( Ψ / 2) )
The area is given by way of the expression E might be known as array component.
Question 36. Define Beam Width Of Major Lobe?
It is defined the perspective between the first nulls (or) it is defined as two times the angle between the primary null and the primary lobe most route.
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Question 37. List Out The Expression Of Beam Width For Broad Side Array And End Fire Array?
For wide facet array the expression for beam width among the first nulls is given by means of,
BWFN = ( ( + / -) 2 λ / n d )
For End fireplace array the expression for beam width between the first nulls is given through,
BWFN = ( ( + / -) 2 ( 2 λ / n d ) )half
Question 38. Differentiate Broad Side And End Fire Array?
In Broad side array antennas are fed in segment δ = zero, in which as in stop fire arrays the antenna elements are fed out of section i.E. δ = - β d.
In large aspect array the most radiation is perpendicular to the route of array axis, wherein as in case of quit hearth array the maximum radiation is directed along the array axis.
Question 39. What Is The Need For The Binomial Array?
The want for a binomial array is
In uniform linear array as the array duration is improved to increase the directivity, the secondary lobes also occurs.
For positive programs, it is pretty acceptable that secondary lobes ought to be eliminated completely or reduced to minimum desirable stage compared to essential lobes.
Question 40. Define Power Pattern?
Graphical representation of the radial element of the poynting vector Sr at a constant radius as a characteristic of angle is called strength density sample or power pattern.
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Question forty one. What Is Meant By Similar Point Sources?
Whenever the version of the amplitude and the segment of the sphere with appreciate to the absolute attitude for any two sources are equal then they may be called similar factor sources.
The maximum amplitudes of the man or woman resources may be unequal.
Question forty two. What Is Meant By Identical Point Sources?
Similar factor assets with same most amplitudes are known as identical factor assets.
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Question 43. What Is The Principle Of The Pattern Multiplication?
The total subject pattern of an array of non isotropic but similar assets is the made from the
Individual supply pattern and
The array pattern of isotropic point assets each located at the section center of the man or woman
source having the identical amplitude and section.
While the total segment sample is the sum of the phase styles of the character source pattern and array pattern.
Question 44. What Is The Advantage Of Pattern Multiplication?
Useful tool in designing antenna.
It approximates the pattern of a complex array with out making lengthy computations.
Question forty five. What Is Tapering Of Arrays?
Tapering of array is a method used for discount of unwanted side lobes. The amplitude of currents in the linear array supply is non-uniform; subsequently the critical source radiates more strength than the ends. Tapering is performed from middle to quit.
Question 46. What Is A Binomial Array?
It is an array in which the amplitudes of the antenna elements inside the array are organized in step with the coefficients of the binomial series.
Question 47. What Are The Advantages Of Binomial Array?
No minor lobes.
Increased beam width.
Maintaining the massive ratio of cutting-edge amplitude in huge arrays is difficult.
Question 48. What Is The Difference Between Isotropic And Non-isotropic Source?
Isotropic source radiates energy in all guidelines but non-isotropic source radiates power only in some desired directions.
Isotropic source is not physically realizable but non-isotropic supply is physically realizable.
Question 49. Define Side Lobe Ratio?
Side Lobe Ratio is defined as the ratio of energy density within the main or main lobe to the electricity density of the longest minor lobe.
Question 50. 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.
Question fifty one. What Do You Understand By Retarded Current?
Since,the fast electric powered dipole is so quick, the cutting-edge that's flowing thru the dipole is believed to be steady at some point of its duration. The effect of this contemporary isn't always felt instant at a distance point handiest after an interval same to the time required for the wave to propagate over the space r is called the retardation time.
The retarded cutting-edge [I]=Io exp( jw' ( t - r / c ) )
Where w'r / c is the segment retardation.
Question fifty two. Define Induction Field?
The induction discipline will predominate at factors close to the present day detail, wherein the distance from the middle of the dipole to the unique point is less. This area is more effective in the place of the cutting-edge element handiest. It represents the power stored in the magnetic field surrounding the contemporary detail or conductor. This area is also called close to discipline.
Question fifty three. Define Radiation Field?
The radiation discipline can be produced at a larger distance from the the current detail, where the gap from the centre of the dipole to the particular factor is very huge. It is likewise referred to as as remote discipline or some distance discipline.
Question fifty four. At What Distance From The Dipole Is The Induction Field Equal To The Radiation Field?
As the distance from the modern-day detail or the short dipole will increase, each induction and radiation fields emerge and begin reducing. However, a distance reaches from the conductor at which each the induction and radiation area turns into same and the unique distance depends upon the wavelength. The fields will therefore have equal amplitude at that specific distance. This distance is given by using r = zero.159 λ.
Question 55. Define Radiation Resistance?
It is described as the fictitious resistance which whilst inserted in collection with the antenna will devour the identical quantity of energy as it's far absolutely radiated. The antenna seems to the transmission line as a resistive factor and that is known as the radiation resistance.
Question 56. Give The Expression For The Effective Aperture Of A Short Dipole?
The effective aperture of a brief dipole is given by using
Ae = 0.119 λ2.
Question fifty seven. What Is A Dipole Antenna?
A dipole antenna may be defined as a symmetrical antenna wherein the 2 ends are at same potential relative to the midpoint.
Question 58. What Is A Half Wave Dipole?
A half of wave antenna is the fundamental radio antenna of metallic rod or tubing or skinny twine which has a physical duration of half of wavelength in free space at the frequency of operation.
Question 59. Give The Expression For The Effective Aperture Of A Half Wave Dipole?
The effective aperture of a half wave dipole is given by using
Ae = 0.Thirteen λ2.
Question 60. What Is The Radiation Resistance Of A Half Wave Dipole?
The radiation resistance of a half of wave dipole is given with the aid of
Rr = seventy three ohm.
Question sixty one. What Is A Loop Antenna?
A loop antenna is a radiating coil of any convenient pass-section of one or greater turns wearing radio frequency modern. It may additionally count on any form (e.G. Square, square, triangular and hexagonal).
Question sixty two. Give An Expression Of Radiation Resistance Of A Small Loop?
Radiation resistance of a small loop is given via
Rr = 31,200 ( A / λ2 )2
Question sixty three. How To Increase The Radiation Resistance Of A Loop Antenna?
The radiation resistance of a loop antenna may be multiplied with the aid of:
Increasing the quantity of turns.
Inserting a ferrite core of very excessive permeability with loop antenna’ s circumference with a view to upward thrust the magnetic area depth referred to as ferrite loop.
Question 64. What Are The Types Of Loop Antennas?
Loop antennas are classified into:
Electrically Small (Circumference < λ / 10 )
Electrically Small (Dimension comparable to λ )
Question 65. What Are Electrically Small Loop Antennas?
Electrically Small loop antennas is one in which the overall period of the loop is less than one-tenth of the wavelength. Electrically Small loop antennas have small radiation resistances that are typically smaller than their loop resistances. They are very bad radiators and seldom hired for transmission in radio conversation.
Question sixty six. List The Applications Of Helical Antenna?
The programs of helical antenna are:
It became the workhouse of space communications for cellphone, tv and records, being hired both on satellites and at ground stations.
Many satellites which include climate satellites, facts relay satellites all have helical antennas.
It is on many different probes of planets and comets, including moon and mars, getting used by myself, in arrays or as feeds for parabolic reflectors, its round polarization and high gain and simplicity making it powerful for area software.
Question sixty seven. Define Sky Wave?
Waves that arrive on the receiver after reflection inside the ionosphere is called sky wave.
Question sixty eight. Define Tropospheric Wave?
Waves that arrive at the receiver after mirrored image from the troposphere area is called Tropospheric wave (i.E. 10 Km from Earth surface).
Question 69. Define Ground Wave?
Waves propagated over other paths close to the earth surface is known as floor wave propagation.
Question 70. What Are The Type Of Ground Wave?
Ground wave labeled into two types.
Question 71. What Is Meant By Space Wave?
It is made of direct wave and ground pondered wave. Also consists of the portion of energy obtained because of diffraction around the earth floor and the mirrored image from the higher ecosystem.
Question 72. What Is Meant By Surface Wave?
Wave that is guided alongside the earth’ s surface like an EM wave is guided by a transmission is referred to as surface wave. Attenuation of this wave is directly stricken by the steady of earth along which it travels.
Question 73. What Is Meant By Fading?
Fading is variation of sign strength arise on line of sight paths because of the atmospheric conditions. It can't be predicted properly.
Question seventy four. What Are The Type Of Fading?
Multi path fading.
Question 75. What Is Inverse And Multi Path Fading?
Inverse bending can also transform line of sight path into an obstructed one.
Multi route fading is as a result of interference among the direct and floor meditated waves as well as interference between are greater paths inside the surroundings.
Question seventy six. What Is Meant By Diversity Reception?
To decrease the fading and to keep away from the multi route interference the technique used are variety reception. It is acquired by means of 3 ways:
Space variety reception.
Frequency range reception.
Question seventy seven. Define Space Diversity Reception?
This method exploits the fact that alerts acquired at special locations do no longer fade collectively. It calls for antennas spaced as a minimum 100λ aside are preferred and the antenna which excessive sign energy in the mean time dominates.
Question seventy eight. Define Frequency Diversity Reception?
This method takes gain of the truth that signals of slightly specific frequencies do no longer fade synchronously. This truth is utilized to reduce fading in radio telegraph circuits.
Question seventy nine. Define Polarization Diversity Reception?
It is utilized in normally in microwave hyperlinks, and it is determined that sign transmitted over the equal course in polarization have unbiased fading styles. In broadband dish antenna gadget, Polarization variety combined with frequency variety reception acquire first-rate outcomes.
Question eighty. What Is Meant By Faraday's Rotation?
Due to the earth’ s magnetic fields, the ionosheric medium turns into anisotropic and the incident aircraft wave coming into the ionosphere will split into regular and additional everyday waves/modes.
When those modes re-emerge from the ionosphere they recombine right into a unmarried plane wave once more. Finally the aircraft of polarization will commonly have modified, this phenomenon is referred to as Faraday's rotation.
Question eighty one. What Are The Factors That Affect The Propagation Of Radio Waves?
Curvature of earth.
Earth’ s magnetic area.
Frequency of the signal.
Plane earth mirrored image.
Question 82. Define Gyro Frequency?
Frequency whose length is same to the duration of an electron in its orbit under the affect of the earths magnetic flux density B.
Question 83. Define Critical Frequency?
For any layer, the best frequency so as to be contemplated lower back for vertical prevalence is
fcr = 9 √Nmax
Question eighty four. Define Magneto-ions Splitting?
The phenomenon of splitting the wave into two one-of-a-kind components (normal and extra-everyday) by using the earths magnetic field is called Magneto-Ions Splitting.
Question 85. Define Luhf?
The lowest beneficial HF for a given distance and transmitter power is defined as the bottom frequency on the way to provide excellent reception for that distance and strength.
It relies upon on:
The powerful radiated energy
Absorption man or woman of ionosphere for the paths between transmitter and receiver.
The required area electricity which in turn relies upon upon the radio noise on the receiving vicinity and form of carrier involved.
Question 86. Define Refractive Index?
It is defined as n = c / Vp
where n = √εr
Question 87. Define Maximum Usable Frequency?
The most Frequency that may be contemplated lower back for a given distance of transmission is known as the maximum usable frequency (MUF) for that distance.
MUF = fcr sec φi
Question 88. Define Skip Distance?
The distance with in which a signal of given frequency fails to be pondered lower back is the skip distance for that frequency. The higher the frequency the more the pass distance.
Question 89. Define Optimum Frequency?
Optimum frequency for transmitting between any two points is therefore selected as some frequency mendacity among about 50 and 85 percentage of the predictedmaximum usable frequency among the ones factors.
Question 90. What Is Antenna Matching?
When the antenna is receiving with a load resistance matched to the antenna radiation resistance, most energy is transferred to the weight and the electricity is likewise re-radiated from the dipole. This is known as antenna matching.
Question ninety one. What Is A Short Dipole?
A brief dipole is one in which the sector is oscillating due to the oscillating voltage and present day. It is known as so, due to the fact the period of the dipole is brief and the modern is almost constant throughtout the whole length of the dipole.
Question ninety two. How Are Fields Created From Short Dipole / Oscillating Dipole?
The dipole has identical expenses of contrary signal oscillating up and down in a harmonic movement. The fees will flow toward every different and electric powered filed traces have been created. When the fees meet on the midpoint, the sphere traces reduce every different and new subject are created.This procedure is spontaneous and so greater filed are created around the antenna. This is how radiations are obtained from a brief dipole.
Question 93. What Are Antenna Field Zones?
The regions containing the radiations that are gift across the antenna are referred to as field zones. The fields round an antenna ay be divided into predominant regions.
Near area sector (Fresnel zone).
Far subject area (Fraunhofer zone).
Question ninety four. What Is Self Impedance And Mutual Impedance?
Self impedance of an antenna is defined as its enter impedance with all different antennas are absolutely eliminated i.E far from it.
The presence of close to with the aid of antenna no.2 induces a modern-day within the antenna no.1 indicates that presence of antenna no.2 adjustments the impedance of the antenna no.1. This effect is referred to as mutual coupling and consequences in mutual impedance.