SRI ESHWAR COLLEGE OF ENGINEERING,COIMBATORE

DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGINEERING

TWO MARK QUESTION WITH ANSWER

SUBJECT NAME: Antenna and Wave Propagation YEAR/SEM : III/VI

SUBJECT CODE: EC6602 PREPARED BY

: Ms.B.MENAKADEVI AP/ECE

UNIT IFUNDAMENTALS OF RADIATION

1. What is magnetic vector potential?The magnetic vector potential is a quantity whose curl gives the magnetic fluxdensity.

B A

Where A is the magnetic vector potential

2. 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 time required for the wave to propagate over distance r. This current is called as retarded current. Retarded

current {I} = I0 ejω(t\r/c), where r/c = retardation time

3. Compare electric scalar potential and magnetic vector potentialS,No Electric scalar potential Magnetic vector potential1. The source for producing

electric potential is chargeThe source for producing magnetic potential is current element

2. Charge is having magnitude only

Current element is having both magnitude and direction

3. E V where V isthe electric scalar

potential

B A where A is the magnetic vector potential

4. Unit is volt/metre Unit is weber/m2

4. Define retardation time.

It is the time required for the wave to propagate over the distance r. It is given by r/c where c = 3 X 108 m/sec

5. Define Antenna.Antenna is a structure associated with the region of transition between guided

wave and free space wave and vice versa

6. Define an Isotropic Antenna.An Isotropic Antenna is the one which radiate energy uniformly in all directions.

7. Define Radiation pattern.Antenna Radiation pattern is a 3 dimensional graph which shows the

variation in actual field strength of EMF at all points which are at equal distance from the antenna.

8. Define Beam solid angle.Beam area or Beam solid angle is the solid angle through which all of

the power radiated by the antenna would stream if P (θ,φ) maintained its maximum value over and zero elsewhere.

9. What are the 2 types of radiation pattern?The 2 types of radiation pattern are (a) Field pattern and (b) power

pattern Field pattern: If the radiation from the antenna is expressed in terms of the field strength (either E or H), then the radiation pattern is called as field pattern.Power pattern: If the radiation pattern from the antenna is expressed in terms of power per unit area, then the resultant pattern is called power pattern.

10. Define Radiation resistance of antenna.Radiation resistance is defined as a ‘Virtual resistance that does not

exist physically but is a quantity coupling the antenna to distant region s of space via a transmission line’.

11.Define Half power beam width.Half power beam width is defined as the angular width measured in the

radiation pattern between points where the power is half of its maximum value. It is also called -3 dB beam width.

12.Define Radiation intensity.The power radiated from an antenna per unit solid angle is called

radiation intensity (U). Its unit is watts per steradian and it is independent of distance.

13.Can same antenna be used satisfactorily for transmission as well as for reception?

Yes. According to Reciprocity principle, the same antenna can be used or transmission and also for reception.

14.Define Directivity of Antenna.Directivity is defined as the ratio of Radiation intensity of test antenna

in a given direction to radiation intensity of isotropic antenna. D = U/U0

Where U= Radiation intensity of test antennaU0 = Radiation intensity of Isotropic antenna’It is also expressed as D

4UPrad

15. What is front to back ratio?Front to Back Ratio (FBR) is defined as the ratio of power radiated in

the desired direction to the power radiated in the opposite directionie. FBR = power radiated in desired direction/power radiated in

opposite direction

16.Define Antenna efficiency.Antenna Efficiency is defined as the ratio of power radiated to the total

input power applied to the antenna.Antenna efficiency, k = Prad/Pin

( dimensionless) Where Prad = Radiated power in wattsPin= Input power in watts

17. Define Reciprocity principle.Reciprocity principle is stated as follows,’ If an emf is applied to the

terminals of antenna no. 1 and the current measured at the terminals of

another antenna no. 2, then an equal current both in amplitude and phase will be obtained at the terminals of antenna no. 1 if the same emf is applied to the terminals of antenna no.2’

18.What do you meant by Antenna aperture?Antenna aperture or equivalent areas are those which are used to

describe the power capturing characteristics of the antenna when a wave impinges on it.

19.Define Effective aperture.Effective aperture is defined as the ratio of power received at the

antenna load terminal to the pointing vector (power density) of the incident wave. Its unit is W/m2.

20.What is the relationship between effective aperture and directivity?The relationship between effective aperture and directivity is D= 4πAe/λ2

21. Write the antenna field zones with the boundaries of an antenna under test.The space surrounding an antenna is divided into 3 regions. They are

Reactive near field Radiation near field (Fresnel) and Far field (Fraunhofer)

The outer boundary of Reactive near field is at a distance R< 0.62√D3/λThe inner boundary of radiation near field (Fresne) is given by R>= 0.62√D3/λ and its outer boundary is R< 2D2/λ

The inner boundary of far field is given by R>=

2D2/λ Where, D= largest dimension of the antennaλ= wavelength in meter

22. What do you meant by effective length of the antenna?The term effective length of an antenna represents the ‘effectiveness

of an antenna as radiator or collector of electromagnetic wave energy’. For a receiving antenna, it is defined as the ratio of induced voltage at the terminals of the receiving antenna under open circuit condition to the incident electric field strength E.

Effective length, le or h = V/E (meter or wavelength)

23.Define Hertzian dipole.Hertzian dipole is defined as a short linear conductor or short electric

dipole whose length is very short compared to wave length (L<<λ) and current is assumed to be constant throughout its length l.

24.What is the effective aperture and directivity of a Hertzian dipole? Effective aperture = 0.119λ2

Directivity = 1.5

25.What is half wave dipole or what is resonant length antenna?Any linear antenna of λ/2 long is called as half wave dipole antenna or

resonant length antenna.

26.What is the effective aperture and directivity of a Half wave dipole antenna? Effective aperture = 0.13λ2

Directivity = 1.63

27.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). It is of less importance.

28.What is radiation field?The radiation field is far field and it varies inversely with distance (1/r). This field

contributes to the flow of energy away from the source. This radiation field or far field is of great importance at large distance.

29.What is quarter wave monopole antenna?The quarter wave monopole antenna is an antenna whose length is one half of a half

wave dipole antenna and is located on a conducting ground plane.

30.What is Yagi Uda Antenna?It is an array of a driven element, a reflector and one or more directors.

31.What do you meant by parasitic elements?The passive elements which are not connected directly to the transmission line but

are electrically coupled are called as parasitic elements.

32.What do you meant by driven elements?Driven element is a active element where the power from the transmission line is

fed or which feeds received power to the receiver.

33.What is the purpose of using more directors in yagi uda antenna? To increase the gain, more directors are used.

34.Why folded dipole antenna is used in yagi uda antenna?The folded dipole has high input impedance. If the distance between driven and

parasitic elements is decreased, it will load the driven element, so input impedance of driven element reduces. But this will compensated ie. raised by the folded dipole.

35.What are the applications of yagi uda antenna?Yagi uda arrays have been used in the HF, VHF, UHF, & microwave frequency

bands. In the HF band, the array is usually constructed using wires & at VHF& UHF frequencies, hollow pipes are used for the construction of yagi uda arrays. At the microwave frequencies the arrays reconstructed using either printed circuit board (PCB) technology or machined out of a metal sheet.

36.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.

37. What are the Advantages of folded dipole? AN.U.2003The 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.

38. 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 .

39.Define balun?. A Balun is used to "balance" unbalanced systems - i.e. those where power flows from an unbalanced line to a balanced line (hence, balun derives from balance to unbalanced).

UNIT II APERTURE AND SLOT ANTENNAS

1. What is a slot antenna?The slot antenna is an opening cut in a sheet of conductor which is energized via a

coaxial cable or waveguide.

2. Which antenna is complementary to the slot antenna?The dipole antenna is complementary to the slot antenna. The metal and air

regions of the slot are interchanged for the dipole.

3. What is the relationship between the terminal impedances of slot and dipole antennas?

ZsZd = η02/4

Where ZS = terminal impedance of slot antenna Zd = Terminal impedance if dipole antennaη0 = Intrinsic impedance of free space = 377 ohms

4. What is the difference between slot antenna and its complementary antenna?i. Polarization are different ie. The electric fields associated with the slot antenna

are identical with the magnetic field of the complementary dipole antenna.ii. The electric field be vertically polarized for the slot and horizontally polarized

for the dipole.iii. Radiation from the back side of the conducting plane of the slot antenna has

opposite polarity from that of complementary antenna.

5. What are the methods of feeding slot antenna?i) Coaxial line feedii) Waveguide feed

6. What are the different methods of feeding slot antennas?Slot antenna can be

a. Waveguide fed slotb. Boxed in slotc. Coaxial transmission line

7. What do you meant by sectoral horn?If flaring (or opened) out is done only in one direction, then it is called as

sectoral horn.

8. What do you meant by pyramidal horn antenna?If flaring is done along both the walls (E &H), then it is called as pyramidal

antenna.

9. What are various feeds used in reflector?a. Dipole antennab. Horn feedc. End fire feedd. Cassegrain feede.

10.What are the advantages of cassegrain feed antenna?1. Reduction in spill over2. Simple in construction3. Quite inexpensive4. Widely used in fixed point to point microwave communication5. Satellite reception and tracking6. Ability to place feed in a convenient location

11.What are the advantages of Microstrip patch antenna?i. These antennas can be flush mounted to metal or other existing surfaces

ii. They only require space for the feed line which is normally placed behind the ground plane.

12.What are the disadvantages of Microstrip patch antenna?iii. Inefficiency

iv. Very narrow frequency bandwidth

13.What are the uses of horn antenna?Horn antenna are extensively used at microwave frequencies under the

condition that power gain needed is moderate. For high power gain, since the horn dimensions become large, so the other antennas like lens or parabolic reflector etc. are preferred rather than horn.

14.What are Microstrip patch antennas?Microstrip antennas are popular for low profile applications at frequencies

above 100 MHz. they usually consists of a rectangular metal patch on a dielectric coated ground plane (circuit board). Hence, a microstrip patch antenna is also called as printed antenna.

15.What are the methods of feeding microstrip antennas?A microstrip patch can be fed either by a microstrip transmission line J or by a

coaxial transmission line. The microstrip line can be etched along with the patch in a single process. In order to access the appropriate impedance point on the patch, a recess is created in the patch.

The depth of the recess is adjusted to achieve the impedance matching. A coaxial transmission line is attached right below the patch, with the inner conductor soldered to the patch and the outer conductor of the coaxial line connected to the ground plane. A patch antenna fed by either a microstrip or a coaxial transmission line has about 2 to 4% input bandwidth.

16.What do you meant by biconical antenna?A biconical antenna consists of 2 infinitely large (L ) cone arranged such that

there axes are in line and the vertices are an infinitesimal distance away from each other.

The 2 cones are fed by a balanced transmission line connected to their vertices. It can be shown that the transmission line formed by the 2 infinite cones. Has characteristic impedance which is only a function of the cone angle but independent of the radial distance from the feed point.

17.What is planar inverted F antenna?It is seen that the electric field along the centre line of a rectangular half wavelength

long microstrip patch antenna is zero. Therefore, we can introduce a perfect electric conductor along this line between the patch and the ground plane without disturbing the fields of the patch, resulting in a quarter wavelength long antenna. This structure is known as a planar inverted F antenna (PIFA).

UNIT IIIANTENNA ARRAYS

1. What are the types of array.?a. Broad side array.

b. End fire array

c. Collinear array.

d. Parasitic array.

2. What is duality of antenna.?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.

3.What is point source?It is the waves originate at a fictitious volumeless emitter source at the

center „O‟ of the observation circle.

4. What is meant by array.?An antenna is a system of similar antennas oriented similarly to get greater

directivity in a desired direction

5. 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. Omni directional antenna.

6. What is Parasitic array.?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.

7. What is the need for the Binomial array.?The need for a binomial array is

i). In uniform linear array as the array length is increased to increase the directivity, the secondary lobes also 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.

8. 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.

9. 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.

10. Define antenna array.A radiating system composed of several spaced and properly phased radiators is

called as an array.

11.Define linear array.An antenna array is said to be linear if the individual antennas of the array are

equally spaced along a straight line.

12.Define uniform linear array.An uniform linear array is one in which the elements are fed with a current of

equal magnitude with uniform phase shift along a line.

13.Define Broadside array.Broadside array is defined as an arrangement in which the principal direction of

radiation is perpendicular to the array axis and also to the plane containing the array element. The phase difference between adjacent elements is zero.

14.Define endfire array.End fire array is defined as an arrangement in which the principal direction of

radiation coincides with array axis.

15.What is array factor?The factor by which the array increases the field strength over that of a single

element radiation the same total power is array factor.

16.What is uniform amplitude distribution?If the sources are in phase and all equal in amplitude, then it is called uniform

amplitude distribution.

17.What is adaptive array?Adaptive array use signal processing algorithms to adapt to user movement,

changes in the radio-frequency environment and co-channel interference.

18. Define Phased Array Antenna A phased array antenna is composed of lots of radiating elements each with a phase shifter. Beams are formed by shifting the phase of the signal emitted from each radiating element, to provide constructive/destructive interference so as to steer the beams in the desired direction

UNIT IVSPECIAL ANTENNAS

1. What are the uses of helical antenna?i. Single or an array of helical antenna is used to receive or transmit the VHF

signals through Ionosphere. Helical antenna is, thus, frequently used for satellite and space probe communications. It has particular applications in space telemetry at the ground end of the telemetry link with ballistic missiles, satellites etc. at HF and VHF bands. The circular polarization is useful in these applications as polarization rotations of waves are produced by the Ionosphere (Faraday Effect).

ii. The wide bandwidth, simplicity, highest directivity and circular polarization of the helical beam antenna have made it indispensable for space communication applications. For, it has been used in transmitting telemetry data from moon to earth remains.

iii. The dimensions of the helix in Axial mode are not critical and thereby resulting in greater bandwidth. This end fire axial mode is more practical as it can achieve circular polarization over a wider bandwidth (normally 2:1) and it is more efficient. Because of circular polarization, helical antenna is capable of receiving signals of arbitrary polarization.

2. What is beam antenna?If three elements array i.e. 1 reflector, 1 driven element and 1 director are used,

then such type of yagi uda antenna is called beam antenna.

3. What are the general characteristics of rhombic antenna?i. If three elements array (i.e. one reflector, one driven and one director) is used,

then such type of yagi uda antenna is generally referred to as beam antenna.ii. It has unidirectional beam of moderate directivity with light weight, low cost and

simplicity in feed system design.iii. With spacing of 0.1 λ to 0.15 λ, a frequency bandwidth of the order of 2 % is

obtained.iv. It provides gain of the order of 8 db or front to back ratio of about 20db.v. If greater directivity is desired, further elements may be used. For example, 5 or

6 elements are used with case and arrays up to 40 can be constructed.vi. It is essentially a fixed frequency device i.e. frequency sensitive and a bandwidth

of about 3% is obtainable. This much bandwidth is sufficient for TV reception.

4.What is frequency independent antenna?An antenna in which the impedance, radiation pattern and directivity remain

constant as a function of frequency is called as frequency independent antenna. Eg. Log periodic Antenna.

5.Why log periodic antenna is named so far?The geometry of log periodic antenna is so chosen that electrical properties must repeat periodically with logarithm of the frequency.

6.What is LPDA?LPDA means Log Periodic Dipole Array. It is defined as an antenna whose electrical properties repeat periodically with logarithm of the frequency.

7.What are the 3 different regions in log periodic antenna and how they are differentiated?

vii. Inactive region – L<λ/2viii. Active region – L= λ/2ix. Inactive reflective region –L> λ/2 14.What

are the applications of log periodic antenna?i. HF Communicationii. Television reception

iii. All round monitoring

8..Define Rhombic Antenna.An antenna which consists of 4 straight wires, arranged in the shape of a

diamond, suspended horizontally above the surface of the earth is called Rhombic antenna. It is otherwise called diamond antenna or traveling wave antenna.

9. What are the 2 types of rhombic antenna design?a.Alignment designb.Maximum field intensity or maximum output design.

10.What are the advantages of Rhombic antenna?a. It is a highly directional broad band antenna with greatest radiated or

received power along the main axis or longer diagonal.b. It is very efficient.c. It is widely employed antenna for radio communication where enough

space necessary for its installation is no problem.d. It is simple and cheap to erect.

e. Its input impedance is twice to that obtainable from a single side radiator.f. Vertical angle of radiation is low and hence these are suitable for long

distance F – layer propagation.g. Short wave antennas of this kind require only a low height.h. Rhombic antennas are untuned and are a useful wideband antenna suitable

for a rapid switching from one working frequency to another frequency.

11.What are the limitations of rhombic antenna?a. It needs large space for installation.

b. Due to minor lobes, transmission efficiency is low.

12.What are the applications of rhombic antenna?i. HF transmission and receptionii. Point to point communication

13.What do you meant by self impedance?Self impedance is defined as the ratio of voltage to current at a pair of

terminals.Z11=R11+jX11

where, R11 = Radiation resistance, X11 = Self reactance

14.What is mutual impedance?It is defined as the negative ratio of emf induced in one antenna to the current

flowing in the antenna.Mutual Impedance, Z21=-V21/I1 (or) Z12=-V12/I2 2

15..What is the need for transposing the lines?In log periodic antenna, it is necessary to introduce 180˚ phase reversal

between elements. This is accomplished by using a twisted transmission line (transposed line). In order to get 180 phase reversal between dipoles, the transmission .line is tranpositioned.

16.What is the effect of decreasing α?The directivity of an antenna increases by means of decreasing the induced

angle α.

17.What are the uses of LPDA?i. Like Rhombic the uses of Log periodic antennas lie mainly in the field of HF

communication where multi band steerable (rotatable) and fixed antennas are generally used. However it has advantage that no power is wasted in terminating resistance.

ii. LPDA is also used for TV reception where only one log periodic design will suffice for all the channels even up to UHF band.

iii. It is best suited for all round monitoring in which case a single log periodic antenna will cover all the higher frequencies bands. If the cost in the installation is no problem.

18.Define a traveling wave antenna.Traveling wave or non resonant antennas are those antennas in which there is

no reflected wave ie. Only incident wave travel in the antenna.

19.What is the main advantage if traveling wave antenna?Traveling wave antenna provides larger bandwidth.

20.What is the type of radiation pattern produced when a wave travels in a wire?Unidirectional radiation pattern is produced when a wave travels in a wire.

21.What is beverage or wave antenna?A single wire antenna terminated in its characteristic impedance may have essentially a uniform traveling wave. This type of antenna is referred to as beverage antenna.

22.What is biconical antenna?The biconical antenna is a double cone antenna which is driven by potential,

charge or an alternating magnetic field at the vertex. In this antenna, both the cones face in opposite direction.

23.How spherical wave are generated?When a voltage V is applied at the input terminals of a biconical antenna, it

will produce outgoing spherical waves. The biconical antenna acts as a guide for the spherical waves.

13.What is turnstile antenna?It is an antenna composed of two dipole antennas perpendicular to each other. They

intersect at their mid points. The current on the 2 dipoles are equal & in phase quadrature.

0

14.What are the salient features of Turnstile antenna?a. Turnstile antenna consists of 2 half wave dipoles which are perpendicular to

each other. The dipoles are excited with a phase difference of 900 with equal currents.

b. The excitation is provided by non-resonant lines of unequal length.c. It produces almost an omni-directional pattern.d. Directivity is improved by the array of turnstile antennas.e. It is best suited to match 70 ohm dual coaxial line.f. It is often used for TV & FM broadcasting in VHF&UHF bands

It produces horizontal polarization.g. The polarization is disturbed due to loss of power. However, the purity of

polarization is improved by super turnstile antennas.h. The super turnstile antenna can be made of 4 flat sheetsi. It is possible to obtain voltage standing wave ratio (VSWR) of about 1.1 over

30% bandwidth.j. It is used as a mast mounted TV transmitting antenna for frequencies about 50

MHz.k. Bandwidth is improved by an array of super turnstile antennas with a spacing of

λ between the elements.l. Array of super turnstile antennas produces more horizontal gain

15.What do you meant by spiral antenna?Spiral is a geometrical shape found in nature. A spiral can be geometrically

described using polar coordinates. Let (r,θ) be a point in the polar coordinate system.The equationr r ea

where, ro and a are positive constants, describes a curve known as a logarithmic spiral or an equiangular spiral.

16.What are the various modes of operation in Helical antenna?a) Normal modeb) Axial mode

17.What are the important parameters to be considered for the design of an helical antenna?

c) Beam widthd) Gaine) Axial ratiof) Impedance

18.List out the applications of helical antenna.Helical antenna is used for

a) VHF transmission such as satellite communicationb) Space telemetry link with ballistic missiles,

satellites etc. 19.What are the advantages of helical antenna?

a) very simpleb) higher directivityc) wideband operation is possibled) circular polarization is obtained

20.Define Lens antenna.An antenna which collimates the incident divergent energy to prevent it from

spreading in undesired direction is called as lens antenna.

21.What are the different types of lens antenna?Lens antenna can be divided into 2 types.

a. Dielectric lens or H plane metal plate lensb. E plane metal plate lens antenna.c.

22.What is dielectric lens antenna?Dielectric lens antennas are the antennas in which the traveling wave fronts

are delayed by lens media.

23.Name the materials used for dielectric lens construction.Polystyrene and polyethylene are the important materials used for dielectric

lens construction.

24. Define E plane metal plate lens antenna.It is an antenna in which the traveling wave fronts are spaced by the lens medium.

25.Define refractive index of lens antenna.It is defined as the ratio of velocity of wave in air to the velocity of wave in lens medium.

26.What are the advantages of stepped dielectric lens antenna?a. It is mechanically strongb. Reduced weightc. Less power dissipation

27.Mention the uses of Lens Antenna.a. Unstepped dielectric lens is a wideband antenna as its shape does not

depend on the wavelength and hence it can be used over a wide frequency range. However this is nit true for dielectric lens antenna which is frequency sensitive. Typical bandwidth for unstepped and stepped lens antenna is 12% and 5% respectively.

b. Both reflectors and lens antennas are commonly used above 1000 MHz. Lens antenna is a microwave device. So it is preferred to be used usually above 3 GHz and not below it.

28.What are the disadvantages of lens antenna?i. Lenses are usually bulky and heavy and present complication in design.

ii. Costlier for the same gain and bandwidth in comparison with reflector.

29.What are the advantages of lens antenna?i. In lens antenna, feed and feed support do not block the aperture as the rays

are transmitted away from the feed.ii. It has greater design tolerance. Ie. Large amount of wrapping and twisting is

possible in lens antenna as waver enters one side and emerges at the other side, maintaining the electrical path length.

It can be used to feed at off the optical axis and hence useful in applications where beam is required to be move angularly with respect to axis.

30.List the different ranges of antenna measurements.The following ranges are used for antenna parameter measurements.1.TEM cell2.GTEM cell3.Outdoor range4.Indoor range5.Reflection range6. Slant range7. Elevated range8. Compact range 9. Anechoic chamber10. Near field range11. Ground range 12. Radar cross section range

31.What is reflection range?In an elevated range, the goal is to minimize the reflected signal from the

ground. In a reflection range, the signal reflected off the ground is used to create constructive interference and hence a uniform wave front in the region of the antenna under test. This can be achieved by careful design of the reflecting surface. Hence the design of a reflection range is more complicated than that of an elevated range. Ground reflection ranges are very useful in the VHF band of frequencies for measuring moderately broad patterns.

32. Define slant range.In a slant range, the transmit antenna is kept very close to the ground and the test

antenna along with its positioner is mounted on a non-conducting tower

33. What is anechoic chamber?A closed chamber can be made reflection-free or echo-free by lining all the

surfaces of the chamber with absorbing material. Such a chamber is known as an anechoic chamber.

34.What are the differences between indoor and outdoor range?S.No. Indoor range Outdoor range1. These are protected from

external EmiThese are susceptible to Emi

2. Space is limited Space is unlimited3. Only small antennas can be

testedAntennas of any size can be tested

4. Ground and other reflections are controlled

Ground and other reflections cannot be controlled fully.

5. They havecontrolled

environment

They have uncontrolled environment

6. They have all weather capability They do not have all weather capability.

35.What are the various factors in which the selection of various ranges depend on? Frequency Cost Accuracy required Size of the antenna and so on.

36.Mention the techniques for measuring gain of antenna?a. Absolute gain measurement

b. Gain transfer method

37.What are secondary antennas? Give examples.Antennas that are not radiators by themselves are called as secondary antennas.

Eg.Cassegrain, Hyperbolic.

UNIT VPROPAGATION OF RADIO WAVES

1.What are the 3 modes of radio wave propagation?

1. Ground wave or surface wave propagation (upto 2 MHz)2. Sky wave or ionospheric wave propagation (Between 2 to 30 MHz)3. Space wave propagation (Above 30MHz)

2.Define ground wave.A wave that is guided along the surface of the earth is called as ground

wave or surface wave.

3.What are the factors that cause attenuation in ground wave?Frequency, surface irregularities, permittivity, conductivity, diffraction

and tilt in the wave front are the various factors that cause attenuation in ground wave.

4.What are the 2 components present in space wave?i)Direct wave – It reaches directly from transmitting antenna to

receiving antenna.ii)Indirect wave – It reaches receiving antenna after reflection from

ground.

5.Define Troposphere.The portion of the atmosphere which extends up to 16 Km from the

earth surface is called Troposphere.

6.Define LOS distance.Line Of Sight distance is a distance in which both the transmitting

and receiving antenna can usually see each other.

7.Define Ionosphere.The upper part of the atmosphere where the ionization is possible is known

as Ionosphere.

8.What are the different layers in Ionosphere?D layer, E layer, F1 layer and F2 layer are the layers in Ionosphere.

9.Define fading.It is the fluctuation in the received signal strength at the receiver or a

random variation in the received signal.

10.How can we minimize fading?The most common method to minimize fading is diversity reception. In this

method, some part of the signal is duplicated and even if one part experiences a deep fade, the other may not.

11.What are the various types of diversity reception? Time diversity reception Frequency diversity reception Space diversity reception

12.What do you meant by magneto Ionic splitting?The earth’s magnetic field splits up the incident waves into 2 different

components. They are Ordinary wave and extra ordinary wave. This phenomenon of splitting of wave into 2 different components is called as magneto ionic splitting.

13.Define Gyro frequency.Gyro frequency fg is defined as the frequency whose period is equal to

the period of revolution of an electron in its circular orbit under the influence of earth’s magnetic flux B.

Fg = Be/2πm

14.Define critical frequency.The critical frequency fc of an ionized layer is defined as the highest frequency

which can be reflected by a particular layer at vertical incidence. It is different for different layer.

Fc = 9√Nm MHzWhere Nm = Maximum electron density in the layer.

15.What is virtual height?Virtual height is defined as the height to which a short pulse of energy sent

vertically upward and traveling with the speed of light would reach taking the same 2 ways travel time as does the actual pulse reflected from the layer.

1 81Nf 2

16.Define MUF.Maximum Usable Frequency MUF is defined as the frequency which can be

reflected back to earth for some specific angle of incidence.Fmuf = fc sec i

where fc = critical frequency; i = angle of incidence

17.Define space wave.Space wave is a wave that reaches the receiver either directly or after

reflection from ground in the earth’s tropospheric region.18.Write down the expression for refractive index.

Refractive Index,

Where, N= Number of electrons per cubic meter f = frequency in Hz

19.What are the factors that affect the propagation of radio waves? The factors that affect the propagation of radio waves are

4. Earth’s magnetic field5. Frequency of the signal6. Curvature of earth7. Permittivity and conductivity