Interview Questions.

Q1. What Is A Loop Antenna?

A loop antenna is a radiating coil of any handy go-segment of one or more turns sporting radio frequency cutting-edge. It may expect any shape (e.G. Rectangular, rectangular, triangular and hexagonal).

Q2. Define Maximum Usable Frequency?

The maximum Frequency that may be reflected lower back for a given distance of trmission is known as the most usable frequency (MUF) for that distance.

MUF = fcr sec φi

Q3. What Is Meant By Polarization?

The polarization of the radio wave can be described by means of route wherein the electric vector E is aligned throughout the passage of atleast one full cycle.Also polarization also can be described the bodily orientation of the radiated electromagnetic waves in area. The polarization are 3 sorts. They are Elliptical polarization ,round polarization and linear polarization.

Q4. Define An Antenna?

Antenna is a trition device or a trducer among a guided wave and a free space wave or vice-versa. Antenna is also stated to be an impedance trforming device.

Q5. How To Increase The Radiation Resistance Of A Loop Antenna?

The radiation resistance of a loop antenna may be increased by:

Increasing the range of turns.

Inserting a ferrite center of very high permeability with loop antenna’ s circumference to be able to rise the magnetic subject depth known as ferrite loop.

Q6. Define Frequency Diversity Reception?

This method takes benefit of the fact that alerts of barely one-of-a-kind frequencies do now not fade synchronously. This truth is applied to reduce fading in radio telegraph circuits.

Q7. Define Aperture Efficiency?

The ratio of the powerful aperture to the physical aperture is the aperture efficiency. I.E Aperture performance = hap = Ae / Ap (dimensionless).

Q8. What Are The Type Of Ground Wave?

Ground wave categorised into two types.

Space wave.

Surface wave.

Q9. Define Gyro Frequency?

Frequency whose period is equal to the length of an electron in its orbit below the affect of the earths magnetic flux density B.

Q10. What Is A Dipole Antenna?

A dipole antenna may be defined as a symmetrical antenna wherein the two ends are at identical ability relative to the midpoint.

Q11. Define Different Types Of Aperture?

Effective aperture (Ae): It is the place over which the power is extracted from the incident wave and added to the load is called powerful aperture. 

Scattering aperture (As): It is the ratio of the reradiated strength to the strength density of the incident wave.

Loss aperture (Ae): It is the place of the antenna which dissipates power as warmness. 

Collecting aperture (Ae): It is the addition of above 3 apertures.

Physical aperture (Ap): This aperture is a degree of the physical length of the antenna.

Q12. Define Power Pattern?

Graphical illustration of the radial factor of the poynting vector Sr at a constant radius as a feature of attitude is called electricity density pattern or energy sample.

Q13. What Is Meant By Diversity Reception?

To minimize the fading and to keep away from the multi route interference the method used are variety reception. It is acquired by three ways:

Space variety reception.

Frequency variety reception.

Polarization diversity.

Q14. What Are The Different Types Of Aperture?

Effective aperture.

Scattering aperture.

Loss aperture.

Collecting aperture.

Physical aperture.

Q15. Define Magneto-ions Splitting?

The phenomenon of splitting the wave into two one of a kind components (normal and extra-ordinary) by using the earths magnetic subject is called Magneto-Ions Splitting.

Q16. What Is Meant By Cross Field?

Normally the electrical discipline E is perpendicular to the route of wave propagation. In a few state of affairs the electric subject E is parallel to the wave propagation that circumstance is referred to as Cross discipline. 

Q17. Define Radiation Field?

The radiation field might be produced at a bigger distance from the the modern-day detail, where the distance from the centre of the dipole to the precise point may be very large. It is likewise referred to as as distant discipline or a long way area.

Q18. Define Space Diversity Reception?

This method exploits the reality that indicators obtained at special locations do no longer fade collectively. It calls for antennas spaced as a minimum 100λ apart are favored and the antenna which excessive signal energy in the mean time dominates.

Q19. What Are The Advantages Of Binomial Array?

Advantage:

No minor lobes.

Disadvantages:

Increased beam width.

Maintaining the big ratio of cutting-edge amplitude in big arrays is tough.

Q20. What Is Collinear Array?

In this array the antenna factors are arranged coaxially by mounting the factors stop to lead to straight line or stacking them one over the opposite with radiation sample circular symmetry. 

Eg. Omnidirectional antenna.

Q21. Define Radiation Resistance?

It is defined as the fictional resistance which whilst inserted in collection with the antenna will consume the equal quantity of energy as it is definitely radiated. The antenna seems to the trmission line as a resistive component and this is referred to as the radiation resistance.

Q22. What Is Meant By Fading?

Fading is variant of sign strength arise online of sight paths due to the atmospheric conditions. It can not be predicted properly.

Q23. What Is Broad Side Array?

Broad facet array is defined as an arrangement in which the foremost path of radiation is perpendicular to the array axis and also the aircraft containing the array detail. 

Q24. What Are The Types Of Array?

Broad facet array.

End hearth array

Collinear array.

Parasitic array.

Q25. What Is Meant By Identical Point Sources?

Similar factor assets with identical maximum amplitudes are known as equal factor resources.

Q26. 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.

Q27. What Is Meant By Front To Back Ratio?

It is described as the ratio of the energy radiated in preferred course to the power radiated inside the contrary direction. I.E FBR = Power radiated in preferred path / power radiated in the contrary direction.

Q28. Differentiate Broad Side And End Fire Array?

In Broad aspect array antennas are fed in section δ = 0, in which as in cease fireplace arrays the antenna factors are fed out of section i.E. δ = - β d.

In large side array the most radiation is perpendicular to the path of array axis, in which as in case of cease fire array the maximum radiation is directed alongside the array axis.

Q29. Define Tropospheric Wave?

Waves that arrive at the receiver after reflection from the troposphere area is known as Tropospheric wave (i.E. 10 Km from Earth floor).

Q30. 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-day measured on the terminals of the some other antenna no.2, then an equal modern-day both in amplitude and phase might be obtained at the terminal of the antenna no.1 if the equal emf is applied to the terminals of antenna no.2.

Q31. What Is Meant By Space Wave?

It is made up of direct wave and floor pondered wave. Also includes the part of strength obtained due to diffraction around the earth floor and the mirrored image from the higher surroundings.

Q32. What Is Point Source?

It is the waves originate at a fictitious extent less emitter source on the center ‘O’ of the observation circle.

Q33. What Is Meant By Beam Area?

The beam region or beam stable attitude or WA of an antenna is given by means of the normalized electricity pattern over a sphere. 

WA = ò ò4p Pn ( q,f ) dW

Where dW = Sin q dq.Df 

Q34. What Are Antenna Field Zones?

The areas containing the radiations which are gift around the antenna are referred to as discipline zones. The fields round an antenna ay be divided into two main regions.

Near field region (Fresnel region).

Far field quarter (Fraunhofer zone).

Q35. What Are The Factors That Affect The Propagation Of Radio Waves?

Curvature of earth.

Earth’ s magnetic discipline.

Frequency of the signal.

Plane earth reflection.

Q36. What Is The Advantage Of Pattern Multiplication?

Useful tool in designing antenna.

It approximates the pattern of a complex array without making lengthy computations.

Q37. Define Radiation Intensity?

The energy radiated from an antenna per unit strong perspective is referred to as the radiation depth U (watts in keeping with steradian or in line with square diploma). The radiation depth is impartial of distance.

Q38. Define Luhf?

The lowest beneficial HF for a given distance and trmitter energy is described as the lowest frequency with a purpose to give nice reception for that distance and strength.

It depends on:

The effective radiated power

Absorption character of ionosphere for the trails among trmitter and receiver.

The required field electricity which in flip depends upon the radio noise at the receiving place and kind of service concerned.

Q39. What Is Meant By Similar Point Sources?

Whenever the variation of the amplitude and the phase of the field with respect to absolutely the perspective for any two sources are identical then they are known as comparable factor resources.

The most amplitudes of the character resources can be unequal.

Q40. What Is The Need For The Binomial Array?

The need for a binomial array is

In uniform linear array as the array period is accelerated to increase the directivity, the secondary lobes also happens.

For certain applications, it's far pretty proper that secondary lobes ought to be eliminated completely or reduced to minimum suited level in comparison to most important lobes.

Q41. Give The Expression For The Effective Aperture Of A Short Dipole?

The powerful aperture of a quick dipole is given via

Ae = 0.119 λ2.

Q42. How Are Fields Created From Short Dipole / Oscillating Dipole?

The dipole has  same fees of opposite signal oscillating up and down in a harmonic motion. The prices will move toward every different and electric powered filed traces were created. When the expenses meet on the midpoint, the sector lines reduce every different and new area are created.This technique is spontaneous and so extra filed are created around the antenna. This is how radiations are received from a short dipole.

Q43. Define Self Impedance?

Self impedance of an antenna is described as its input impedance with all other antennas are absolutely eliminated i.E far from it.

Q44. What Is Meant By Uniform Linear Array?

An array is linear when the factors of the array are spaced similarly alongside the directly line. If the factors are fed with currents of identical significance and having a uniform modern phase shift along the road, then it's far referred to as uniform linear array.

Q45. What Are The Type Of Fading?

Two sorts:

Inverse fading.

Multi path fading.

Q46. Define Beam Width Of Major Lobe?

It is defined the attitude among the primary nulls (or) it's far defined as twice the angle among the first null and the principal lobe maximum direction.

Q47. What Are The Field Zones?

The fields round an antenna can be divided into  predominant areas.

Near subject area (Fresnel quarter)

Far subject quarter (Fraunhofer sector)

Q48. What Is Tapering Of Arrays?

Tapering of array is a way used for reduction of undesirable side lobes. The amplitude of currents inside the linear array source is non-uniform; hence the valuable supply radiates greater electricity than the ends. Tapering is achieved from center to cease.

Q49. Define Side Lobe Ratio?

Side Lobe Ratio is defined because the ratio of energy density within the major or fundamental lobe to the electricity density of the longest minor lobe.

Q50. Define Ground Wave?

Waves propagated over other paths near the earth floor is known as ground wave propagation.