Results
Q1. The ideal length for a Marconi aerial for a frequency of 406 MHz is:
18.5 cm
Q2. An AC will be induced:
in a wire, parallel to the wire fed with an AC, but remote from it. Explanation When alternating current of suitably high frequency is fed into a given wire (transmitting antenna), the energy is not confined to the metal of the antenna but radiates out into space as electromagnetic energy and will also induce alternating current in the second wire, which is parallel and next to it.
Q3. What characteristic describes the radar beam of a parabolic antenna?
Directional Parabolic antennae are used as directional antennae; therefore they direct their narrow pencil beam main lobe into one specific direction.
Q4. Comparing a parabolic reflector with a flat plate antenna of the same size
the flat plate antenna generates less side lobes than the parabolic reflector.
Parabolic reflectors create more side lobe activity, which results in a waste of energy and a smaller range of the main beam.
Newer technologies use flat plate (slotted) antennas with a less side lobe activity and a greater range (more energy in the beam).
Another advantage is a smaller size of the antenna and less weight for creating the same performance.
Q5. Considering a primary radar system, what kind of aerials are used?
One directional antenna both for transmitting and for receiving. The primary radar operates on the echo-principle: ground radar facility transmits pulses of radio waves that are reflected from the aircraft back to the radar facility. The pulses must have sufficient energy to “travel” to the aircraft and back. There is no equipment required on board the aircraft as the radio waves get reflected from the aircraft structure itself. … Both the primary and secondary radars operating on the pulse principle use a directional antenna that is used both for the transmitting and receiving of the signals. …
Q6. XX Which of the following statements is true?
Bandwidth must be reduced in order to reduce noise Narrower bandwidth does not always reduce noise-it can limit signal reception.
Q7. An electromagnetic wave has two types of energy field:
an E electrical field and an H magnetic field. Explanation: An electromagnetic wave consists of two perpendicular fields: E-field: Electric field H-field: Magnetic field These fields oscillate at right angles to each other and to the direction of wave propagation.
Q8. ** The advantage of the use of slotted antennas in modern radar technology is to:
virtually eliminate lateral lobes and as a consequence concentrate more energy in the main beam. The main advantage of a slotted scanner (also called “flat plate” antenna or “slotted planar array”) is that it produces a much narrower beam and eliminates most of the lateral lobes => consequently concentrates more energy into the main beam and thus improving the resolution and reducing the power output required.
Q9. What is necessary to enable an antenna to transmit an electromagnetic wave?
The antenna has to be fed with alternating current of high frequency. When alternating current of suitably high frequency is fed into a given wire (transmitting antenna), the energy is not confined to the metal of the antenna but radiates out into space as electromagnetic energy and will also induce alternating current in the second wire, which is parallel and next to it.
Q10. The ideal length of a half-wave dipole for a frequency of 112 MHz is:
1.3383 m
Q11. ** Helical antennas are used by GPS satellites for the following reasons:
because the signal has a circular polarization. Ref Ch 1: Explanation A helical antenna is an antenna consisting of a conducting wire wound in the form of a helix. … Helical antennas can operate in one of two principal modes: … • axial mode (VHF up to SHF), commonly used in satellite communication systems, which use circularly polarised radio waves…
Q12. The ideal length of a half-wave dipole for a frequency of 75 MHz is:
1.9 m
Q13. An electromagnetic wave consists of an oscillating electric field (E) and an oscillating magnetic field (H). Their propagation speed is:
the speed of light.
Q14. A radio wave with a horizontal magnetic component would be best received by a aerial?
Vertical
Q15. Comparing a parabolic reflector with a flat plate antenna of the same size?
Q16. Given a wire fed with alternating current and a second wire parallel to, but remote from it. The results will be:
the first wire will radiate electromagnetic waves into space and alternating current will be induced in the second wire. Explanation When alternating current of suitably high frequency is fed into a given wire (transmitting antenna), the energy is not confined to the metal of the antenna but radiates out into space as electromagnetic energy and will also induce alternating current in the second wire, which is parallel and next to it.
Q17. Which of the following lists only includes directional antennas?
Loop antenna, parabolic antenna, slotted planar antenna, helical antenna. sense aerial is also known as dipole aerial. — you will study in ADF. A directional antenna or beam antenna is an antenna which radiates greater power in one or more directions allowing for increased performance on transmit and receive and reduced interference from unwanted sources. … Examples of directional antennas are: loop antennas, parabolic antennas, slotted antennas, phased array antennas and helical antennas.
Q18. A horizontally polarized electromagnetic wave:
has the E field horizontal. plane of polarization is plane Of E
Q19. The polarization of an electromagnetic wave describes:
the orientation of the plane of oscillation of the electrical component of the wave with regard to its direction of propagation.
Q20. ** A radio wave with a horizontal magnetic component would be best received by a dipole antenna.
vertical In the case of this question, we have a horizontal magnetic component of the signal, therefore the electrical component of the signal will be vertical => we have a vertical polarization. Therefore, for the best possible reception, the receiver antenna must also be vertical to receive the electrical component of the signal.
Q21. A loop antenna is commonly used in:
ADF receivers.
Q22. The simplest type of antenna construction is a:
dipole antenna which is a wire of length equal to one half of the wavelength.
Q23. What describes polarization?
Orientation of the plane of oscillation of the electrical component (E) of the electromagnetic wave.
Q24. The gain of an aerial is its ability to?
Compensate for attenuation Antenna gain helps compensate for attenuation by focusing energy more efficiently, thereby maintaining signal strength over longer distances.
Q25. A half wave dipole aerial suitable for transmitting an RF signal at 18 MHz should have an effective length of?
8.33 meters
Q26. ** Which of the following is not an advantage of a slotted antenna (phased array)?
Directivity Slotted antennas or phased array antennas offer several advantages such as: Reduced side lobes (less unwanted radiation) Improved resolution (due to better beam shaping) Reduced power requirement (efficient beam steering) However, directivity is not considered an advantage specific to slotted antennas-because high directivity is a general feature of many directional antennas, not unique to slotted or phased arrays.
Q27. Which of the following statements is correct in respect of a RF signal:
the electrical component of the signal is parallel to the antenna.
Q28. ** The ideal length for a Marconi aerial for a frequency of 2400 MHz is:
3.125 cm
Q29. An electromagnetic wave consists of an oscillating electric field (E) and an oscillating magnetic field (H). Which statement is correct?
when signal passes through the antenna, the “E” field is parallel to the wire and the “H” field is perpendicular to the wire.
Q30. #A disadvantage of directivity is:
side lobes
Q31. XX Feeder lines are of the following types?
Explanation: Co-axial cables are commonly used for frequencies up to about 3 GHz (3000 MHz) because they are flexible and easy to install. Waveguides are more efficient for very high frequencies above 3000 MHz (microwave frequencies) due to lower loss and better power handling.
Key Points:
Co-axial: Suitable for RF signals up to 3 GHz.
Waveguide: Used for microwave frequencies > 3 GHz.
