WorksheetsWGA - A2 - QUIZ
Total questions: 30
Worksheet time: 56mins
Radiation resistance of a small dipole current element of length l at a frequency of 3 GHz is 3 ohms. If the length is changed by 1%, then the percentage change in the radiation resistance, rounded off to two decimal places, is ---------%.
1.5
2.5
1.98
0
Consider the following statements with reference to dipole arrays:
1) In broadside array, all the dipoles are fed in the same phase from the same source.
2) In end-fire array, the magnitude of the current in each element is same and there is no phase difference between these currents.
Which of the above statements is/are correct? [GATE 2019]
1 only
2 only
Both 1 and 2
Neither 1 nor 2
Two communication antennas A and B, are operating at 300 MHz and other at 3 GHz respectively and having same gain, are illuminated with identical flux density of -100 dBW/m2. What is the relation between the received powers (PA : PB)?
1 : 10
10 :1
1 : 100
100 : 1
A rectangular waveguide of width w and height h has cut-off frequencies for TE10 and TE11 modes in the ratio 1 :2 . The aspect ratio w/h, rounded off to two decimal places, is --------.
1.5
2.5
1.71
0
For a dipole antenna
The radiation intensity is maximum along the normal to the dipole axis
The current distribution along its length is uniform irrespective of the length
The effective length equals its physical length
The input impedance is independent of the location of the feed – point
An antenna when radiating, has a highly directional radiation pattern. When the antenna is receiving its radiation pattern.
Is more directive
Is less directive
Is the same
Exhibits no directivity all
The vector 𝐻 in the far field of an antenna satisfies
∇.𝐻 = 0 𝑎𝑛𝑑 ∇ × 𝐻 = 0
∇.𝐻 ≠ 0 𝑎𝑛𝑑 ∇ × 𝐻 ≠ 0
∇.𝐻 = 0 𝑎𝑛𝑑 ∇ × 𝐻 ≠ 0
∇.𝐻 ≠ 0 𝑎𝑛𝑑 ∇ × 𝐻 = 0
The radiation resistance of a circular loop of one turn is 0.01Ω. The radiation resistance of five turns of such a loop will be
0.002 Ω
0.01 Ω
0.05 Ω
0.25 Ω
An antenna in free space receives 2𝜇 𝑊 of power when the incident electric field is 20 mV/m rms. The effective aperture of the antenna is
0.005 𝑚2
0.05 𝑚2
1.885 𝑚2
3.77 𝑚2
The far field of an antenna varies with distance r as
1/r
1/r2
1/r3
1/√𝑟
If the diameter of a 𝜆/2 dipole antenna is increased from 𝜆/100 to 𝜆/50 then its
Bandwidth increases
Bandwidth decreases
Gain increases
Gain decreases
The line – of – sight communication requires the transmit and receive antennas to face each other. If the transmit antenna is vertically polarized for best reception the receiver antenna should be
Horizontally polarized
Vertically polarized
At 450 with respect to horizontal polarization
At 450 with respect to vertical polarization
Consider a lossless antenna with a directive gain of +6 dB. If 1 mW of power is fed to it the total power radiated by the antenna will be
4 mW
1 mW
7 mW
1/4 mW
A transmission line is feeding 1 Watt of power to a horn antenna having a gain of 10 dB. The antenna is matched to the transmission line. The total power radiated by the horn antenna into the free space is
10 Watts
1 Watt
0.1 Watt
0.01 Watt
For a Hertz dipole antenna, the half power beam width (HPBW) in the E – plane is
3600
1800
900
450
The radiation pattern of an antenna in spherical co – ordinates is given by 𝐹(𝜃) = 𝑐𝑜𝑠4𝜃 ; 0 ≤ 𝜃 ≤ 𝜋/2 The directivity of the antenna is
10 dB
12.6 dB
11.5 dB
18 dB
For an antenna radiating in free space, the electric field at a distance of 1 km is found to be 12 mV/m. Given that intrinsic impedance of the free space is 120 πΩ, the magnitude of average power density due to this antenna at a distance of 2 km from the antenna (in nW/m2) is ----------------.
47.7 nW/m2
4.77 nW/m2
477 nW/m2
0.477 nW/m2
Match column A with column B.
Column A
1. Point electromagnetic source
2. Dish antenna
3. Yagi – Uda antenna
Column B
P. Highly directional
Q. End fire
R. Isotropic
1-P,2-Q,3-R
1-R,2-P,3-Q
1-Q,2-P,3-R
1-Q,2-R,3-P
The directivity of an antenna array can be increased by adding more antenna elements, as a larger number of elements
Improves the radiation efficiency
Increases the effective area of the antenna
Results in a better impedance matching
Allow more power to be transmitted by the antenna
The electric field E and the magnetic field H of a short dipole antenna satisfy the condition
The r component of E is equal to zero
Both r and 𝜃 components of H are equal to zero
The 𝜃 component of E dominates the r component in the far – field region
The 𝜃 and ∅ components of H are of the same order of magnitude in the near – field region
Two isotropic antennas are separated by two wavelengths. If both the antennas are fed with currents of equal phase and magnitude, the number of lobes in the radiation pattern in the horizontal plane are
2
4
6
8
In a broad side array of 20 isotropic radiators, equally spaced at 𝜆 /2, the beam width between first nulls is
51.3 degrees
11.46 degrees
22.9 degrees
102.6 degrees
Two dissimilar antennas having their maximum directivities equal
Must have their beam widths also equal
Cannot have their beam widths equal because they are dissimilar antennas
May not necessarily have their maximum power gains equal
Must have their effective aperture areas (capture areas) also equal
The beam width – between – first – nulls of a uniform linear array of N equally – spaced (element spacing = d) equally – excited antennas is determined by
N alone and not by d
d alone and not by N
The ratio (N/d)
The product (Nd)
A transverse electromagnetic wave with circular polarization is received by a dipole antenna. Due to polarization mismatch, the power transfer efficiency from the wave to the antenna is reduced to about
50%
35.3%
25%
0%
A 1 km long microwave link uses two antennas each having 30dB gain. If the power transmitted by one antenna is 1 W at 3 GHz, the power received by the other antenna is approximately
98.6 µ W
76.8 µ W
63.4 µ W
55.2 µ W
A parabolic dish antenna has a conical beam 20 wide. The directivity of the antenna is approximately
20 dB
30 dB
40 dB
50 dB
The half – power bean widths (HPBW) of an antenna in the two orthogonal planes are 1000 and 600 respectively. The directivity of the antenna is approximately equal to
2 dB
5 dB
8 dB
12 dB
A medium wave radio transmitter operating at a wavelength of 492 m has a tower antenna of height 124 m. What is the radiation resistance of the antenna?
25 Ω
36.5 Ω
50 Ω
73 Ω
A person with a receiver is 5 km away from the transmitter. What is the distance that this person must move further to detect a 3 – dB decrease in signal strength?
942 m
2070 m
4978 m
5320 m
