# 300+ [UPDATED] Antenna Interview Questions and Answers

Q1. 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).

Q2. Define Maximum Usable Frequency?

The maximum Frequency that can be reflected back for a given distance of trmission is called the maximum usable frequency (MUF) for that distance.

MUF = fcr sec φi

Q3. What Is Meant By Polarization?

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.

Q4. Define An Antenna?

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

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

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

• Increasing the number of turns.
• Inserting a ferrite core of very high permeability with loop antenna’ s circumference which will rise the magnetic field intensity called ferrite loop.

Q6. Define Frequency Diversity Reception?

This method takes advantage of the fact that signals of slightly different frequencies do not fade synchronously. This fact is utilized to minimize fading in radio telegraph circuits.

Q7. Define Aperture Efficiency?

The ratio of the effective aperture to the physical aperture is the aperture efficiency. i.e Aperture efficiency = hap = Ae / Ap (dimensionless).

Q8. What Are The Type Of Ground Wave?

Ground wave classified into two types.

• Space wave.
• Surface wave.

Q9. Define Gyro Frequency?

Frequency whose period is equal to the period of an electron in its orbit under the influence of the earths magnetic flux density B.

Q10. What Is A Dipole Antenna?

A dipole antenna may be defined as a symmetrical antenna in which the two ends are at equal potential relative to the midpoint.

Q11. Define Different Types Of Aperture?

Effective aperture (Ae): It is the area over which the power is extracted 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.

Q12. Define Power Pattern?

Graphical representation of the radial component of the poynting vector Sr at a constant radius as a function of angle is called power density pattern or power pattern.

Q13. What Is Meant By Diversity Reception?

To minimize the fading and to avoid the multi path interference the technique used are diversity reception. It is obtained by three ways:

• Space diversity reception.
• Frequency diversity 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 different components (ordinary and extra-ordinary) by the earths magnetic field is called Magneto-Ions Splitting.

Q16. What Is Meant By Cross Field?

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.

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.

Q18. Define Space Diversity Reception?

This method exploits the fact that signals received at different locations do not fade together. It requires antennas spaced at least 100λ apart are preferred and the antenna which high signal strength at the moment dominates.

Q19. What Are The Advantages Of Binomial Array?

• No minor lobes.

• Increased beam width.
• Maintaining the large ratio of current amplitude in large arrays is difficult.

Q20. What Is Collinear Array?

In this array the antenna elements are arranged coaxially by mounting the elements end to end in straight line or stacking them one over the other with radiation pattern circular symmetry.

Eg. Omnidirectional antenna.

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 trmission line as a resistive component and this is known as the radiation resistance.

Q22. What Is Meant By Fading?

Fading is variation of signal strength occur on line of sight paths as a result of the atmospheric conditions. It can not be predicted properly.

Q23. What Is Broad Side Array?

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.

Q24. What Are The Types Of Array?

• End fire array
• Collinear array.
• Parasitic array.

Q25. What Is Meant By Identical Point Sources?

Similar point sources with equal maximum amplitudes are called identical point sources.

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 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.

Q28. Differentiate Broad Side And End Fire Array?

• In Broad side array antennas are fed in phase δ = 0, where as in end fire arrays the antenna elements are fed out of phase i.e. δ = – β d.
• In broad side array the maximum radiation is perpendicular to the direction of array axis, where as in case of end fire array the maximum radiation is directed along the array axis.

Q29. Define Tropospheric Wave?

Waves that arrive at the receiver after reflection from the troposphere region is called Tropospheric wave (i.e. 10 Km from Earth surface).

Q30. What Is Meant By Reciprocity Theorem?

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.

Q31. 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.

Q32. What Is Point Source?

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

Q33. What Is Meant By Beam Area?

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 dq.df

Q34. What Are Antenna Field Zones?

The regions containing the radiations that are present around the antenna are called field zones. The fields around an antenna ay be divided into two principal regions.

• Near field zone (Fresnel zone).
• Far field zone (Fraunhofer zone).

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

• Curvature of earth.
• Earth’ s magnetic field.
• 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 complicated array without making lengthy computations.

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.

Q38. Define Luhf?

The lowest useful HF for a given distance and trmitter power is defined as the lowest frequency that will give satisfactory reception for that distance and power.

It depends on:

• Absorption character of ionosphere for the paths between trmitter and receiver.
• The required field strength which in turn depends upon the radio noise at the receiving location and type of service involved.

Q39. 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.

Q40. What Is The Need For The Binomial Array?

The need for a binomial array is

• In uniform linear array as the array length is increased to increase the directivity, the secondary lobes also occurs.
• For certain applications, it is highly desirable that secondary lobes should be eliminated completely or reduced to minimum desirable level compared to main lobes.

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

The effective aperture of a short dipole is given by

Ae = 0.119 λ2.

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

The dipole has two equal charges of opposite sign oscillating up and down in a harmonic motion. 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 filed are created around the antenna. This is how radiations are obtained from a short dipole.

Q43. Define Self Impedance?

Self impedance of an antenna is defined as its input impedance with all other antennas are completely removed i.e away from it.

Q44. What Is Meant By Uniform Linear Array?

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.

Q45. What Are The Type Of Fading?

Two types:

Q46. 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.

Q47. What Are The Field Zones?

The fields around an antenna may be divided into two principal regions.

• Near field zone (Fresnel zone)
• Far field zone (Fraunhofer zone)

Q48. 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.

Q49. Define Side Lobe Ratio?

Side Lobe Ratio is defined as the ratio of power density in the principal or main lobe to the power density of the longest minor lobe.

Q50. Define Ground Wave?

Waves propagated over other paths near the earth surface is called ground wave propagation.