5710433
Description
Quiz by sergiocarretero, updated more than 1 year ago
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Created by sergiocarretero
almost 8 years ago
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Question 1
Question
Consider the following problem, (all the units are in meters): Two ideal monopoles of 0.25 length are installed perpendicularly on a PEC plane whose four corners are located in the following points: (-2,-2,0), (2,-2,0), (-2,2,0) and (2,2,0). The base of the first monopole is in (-1,0,0) and the second in (1,0,0). The first monopole is installed in the upper side of the PEC plane (+Z) and the second in the lower side (-Z).
Answer
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The coupling level between the monopoles at 300 MHz is the same that would be found in the following problem at 3 GHz: i. Two ideal monopoles of 0.25 length installed perpendicularly on a PEC plane which four corners are in following points: (-0.2,-0.2,0), (0.2,-0.2,0), (-0.2,0.2,0) and (0.2,0.2,0). The base of the first monopole is in (-0.1,0,0) and the second in (0.1,0,0). The first monopole is installed in the upper side of the PEC plane (+Z) and the second in the lower side (-Z)
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The coupling level between the monopoles at 300 MHz is the same that would be found in the following problem at 150 MHz: i. Two ideal monopoles of 0.5 length installed perpendicularly on a PEC plane which four corners are in following points: (-4,-4,0), (4,-4,0), (-4,4,0) and (4,4,0). The base of the first monopole is in (-2,0,0) and the second in (2,0,0). The first monopole is installed in the upper side of the PEC plane (+Z) and the second in the upper side (+Z).
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The coupling level between the monopoles at 300 MHz is the same that would be found in the following problem at 600 MHz: i. Two ideal monopoles of 0.5 length installed perpendicularly on a PEC plane which four corners are in following points: (-4,-4,0), (4,-4,0), (-4,4,0) and (4,4,0). The base of the first monopole is in (-2,0,0) and the second in (2,0,0). The first monopole is installed in the upper side of the PEC plane (+Z) and the second in the lower side (-Z).
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None of them.
Question 2
Question
From the following sentences, select the one's that are true:
Answer
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The spurious radiated emissions from an antenna are generally produced by the non-linear response of the transmitter antenna
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Loop antennas and classical blades have the same radiation pattern. We can always choose between them for a particular system, if both antennas have enough bandwidth
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The maximum directivity of an antenna never will be lower than 0 dBi.
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We have found a direct coupling problem due to System I (Tx) interferes System II (Rx). This problem can be solved adding a filter between the antenna of system II and its receiver
Question 3
Question
We have detected the following malfunction:
Each time we are transmitting with the radio in a channel centered in 409 MHz, we find problems with the GPS. We have reduced the output power of the radio, and the problem disappears. We do not have problems between the radio and the GPS in other channels, separated 50 MHz between them. The GPS is using L2 band (1227.60 MHz). The length of the GPS cable is 10 meters and the gain of the preamplifier of the GPS antenna is 20 dB. The cable insertion loss is 0.5 dB per meter.
Which proposals can solve this problem?
Answer
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We propose to change the GPS antenna for another with a better filter
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We propose to reduce the spurious emission of the radio
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Use suppression on the radio and blanking on the GPS
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Separate the GPS antenna from the radio antenna
Question 4
Question
Concerning the directive/directional antennas, which one(s) are true:
Answer
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The main advantage of an electronically scan array antenna compared to a mechanical scan reflector antenna is the simplicity of electronically steering of the radiation pattern, which enables to design a simpler antenna avoiding the integration of motors, gears, encoders…
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We have designed and integrated a satcom system working in X band based on a reflector+subreflector antenna. We have to move to Ku band. In general, we cannot reuse the radome.
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We have designed and integrated a satcom system working in X band based on a reflector+subreflector antenna. We have to move to Ku band. In general, we cannot reuse the main reflector and subreflector of the antenna.
Question 5
Question
Concerning the impedance of an antenna, which one(s) are true:
Answer
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There is a relation between the impedance of the antenna and efficiency factor
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This parameter only depends on and is fixed by the matching network
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The impedance of an antenna is usually measured so as to check the correct installation of an antenna
Question 6
Question
Concerning the antennas used for V/UHF communication systems, which one(s) are true:
Answer
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The active or tuned antennas are the best solution in terms of weight for a V/UHF communication system.
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The size of an active or tuned antenna is smaller, but we have a strong impact in the performance (gain) of the antenna. This loss of performance can be typically assumed by the aeronautical communication systems.
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The active or tuned antennas are better for low frequencies both in terms of performance (gain) and size, although the weight is slightly penalized.
Question 7
Question
Concerning the use of electromagnetic simulation for the integration of antennas in A/V, which one(s) are true:
Answer
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This technology is not mature enough and it is always necessary to perform measurements of the antennas at A/V level.
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The shape of the radiation patterns of low-gain omnidirectional antennas strongly depends on the geometry of the aircraft, even much more that antenna itself.
Question 8
Question
Which value of bonding shall be typically met in the installation of antennas:
Answer
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<0.25 mΩ.
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<2.5 Ω.
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2.5 mΩ (5 mΩ max).
Question 9
Question
In the task of antenna location, which one(s) is(are) true:
Answer
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The efficiency radiation of the antenna must be optimised, in the general case, by choosing the best location for the installation of the antenna.
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The performance of the antenna installed on the aircraft is assessed, typically using electromagnetic simulation, to estimate the radiation patterns (coverage) of the antenna installed in a predefined location
Question 10
Question
From the following sentences, select the ones that are true:
Answer
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The electric field is tangent (parallel) to the surface of perfect magnetic conductors
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The magnitude of the scattering field behind a perfect conducting object of a few wavelengths size being illuminated with a radar plane wave is very low and it is the cause of the “shadow" behind the object.
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The electric field is perpendicular to the surface of perfect electric conductors
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The magnetic field is perpendicular to the surface of perfect magnetic conductors.
Question 11
Question
We need to test a system which is basically a transmitter and an antenna installed on an aircraft. The maximum TX power is 314W in average and the antenna maximum directivity, installed on the structure, is 12 dB and its efficiency factor 0.25. We need to use, for our test, some equipments which we know that above 4 W/m2 power density in the frequency band used by our system (3GHz), present malfunctions:
Answer
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We decide to deploy our equipments 20 meters away from the antenna, in order to avoid problems and keep 6 dB of security margin.
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We estimate that 20 meters from the antenna the power density would be around 4W/m2.
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We estimate that 10 meters from the antenna the power density would be around 8W/m2.
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We decide to deploy our equipments 10 meters away from the antenna, in order to avoid problems and keep 6 dB of security margin.
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