Smith chart is based on the polar plot of:
D. Voltage reflection co-efficient
Explanation: let the reflection co-efficient be expressed in terms of magnitude and direction. Magnitude is plotted as radius from the center of the chart, and the angle is measured in counter clockwise direction from the right hand side. Hence, smith chart is based on the polar pot of voltage reflection co-efficient.
Normalized impedance of 0.3+j0.4 lies in the:
A. Upper half of the impedance smith chart
B. Lower half of the impedance smith chart
C. Horizontal line of the chart
D. None of the above
Explanation: In the impedance smith chart, the upper part of the smith chart refers to positive reactance or inductive reactance. Hence, the given point lies in the upper half of the smith chart corresponding to the intersection of circles r=0.3 and r=0.4.
If an antenna has a directivity of 16 and radiation efficiency of 0.9, then the gain of the antenna is:
Explanation: Gain of an antenna is given by the product of radiation efficiency of the antenna and the directivity of the antenna. Product of directivity and efficiency thus gives the gain of the antenna to be 16.2.
Gain of an antenna is always greater than the directivity of the antenna.
Explanation: Gain of an antenna is always smaller than the directivity of an antenna. Gain is given by the product of directivity and radiation efficiency. Radiation efficiency can never be greater than one. So gain is always less than or equal to directivity.
A rectangular horn antenna has an aperture area of 3λ × 2λ. Then the maximum directivity that can be achieved by this rectangular horn antenna is:
A. 24 dB
B. 4 dB
C. 19 dB
D. Insufficient data
With an increase in operating frequency, the background noise temperature:
C. Remains constant
D. Remains unaffected
Explanation: The plot of frequency v/s background noise temperature shows that with the increase of the signal frequency, the background noise temperature increases. Also, with the increase of the elevation angle from the horizon, background noise temperature increases.
The noise temperature of an antenna is given by the expression:
A. radTb + (1-rad) Tp
B. (1-rad) TP
D. None of the above
Explanation: The noise temperature of an antenna is given by the expression radTb + (1-rad) Tp. here, Tb is the brightness temperature and Tp is the physical temperature of the system. rad is the radiation efficiency. Noise temperature of a system depends on these factors.
Low is the G/T ratio of an antenna, higher is its efficiency.
Explanation: In the G/T ratio of an antenna, G is the gain of an antenna and T is the antenna noise temperature. Higher the G/T ratio of an antenna better is the performance of the antenna.
_________ has a constant power spectral density.
A. White noise
B. Gaussian noise
C. Thermal noise
D. Shot noise
Explanation: Thermal noise has a power spectral density for a wide range of frequencies. Its plot of frequency v/s noise power is a straight line parallel to Y axis.
Antennas are bidirectional devices.
Explanation: Antennas can be used both as transmitters and receivers. As transmitters they radiate energy to free space and as receivers they receive signal from free space. Hence, they are called bidirectional devices as they are used at both transmitting end and receiving end.
Dipole antennas are an example for:
A. Wire antennas
B. Aperture antennas
C. Array antennas
D. None of the mentioned
Explanation: Dipoles, monopoles, oops, Yagi-Uda arrays are all examples for wire antennas. These antennas have low gains, and are mostly used at lower frequencies.
_________ antennas consist of a regular arrangement of antenna elements with a feed network
A. Aperture antennas
B. Array antennas
C. Printed antennas
D. Wire antennas
Explanation: Array antennas consist of a regular arrangement of antenna elements with a feed network. Pattern characteristics such as beam pointing angle and side lobe levels can be controlled by adjusting the amplitude and phase excitation of array elements.
_________ of an antenna is a plot of the magnitude of the far field strength versus position around the antenna.
A. Radiation pattern
C. Beam width
D. None of the mentioned
Explanation: Radiation pattern of an antenna is a plot of the magnitude of the far field strength versus position around the antenna. This plot gives the detail regarding the region where most of the energy of antenna is radiated, side lobes and beam width of an antenna.
Antennas having a constant pattern in the azimuthal plane are called _____________
A. High gain antenna
B. Omni directional antenna
C. Unidirectional antenna
D. Low gain antenna
Explanation: Omni directional antennas radiate EM waves in all direction. If the radiation pattern for this type of antenna is plotted, the pattern is a constant signifying that the radiated power is constant measured at any point around the antenna.
Beamwidth and directivity are both measures of the focusing ability of an antenna.
If the beam width of an antenna in two orthogonal planes are 300 and 600. Then the directivity of the antenna is: