1. Which type of Antenna used in SONAR?
Ans. SONAR antennas (synthetic aperture SONAR) are used in sound detection ranging and navigation.
2. What is Gunn diode and tell its uses?
Ans. A Gunn diode, also known as a transferred electron device (TED), is a form of diode, a two-terminal passive semiconductor electronic component, with negative resistance, used in high-frequency electronics.
3. What is the frequency range of optical fibre?
Ans. Optical fibre has a frequency range from 180-THz to 330-THz.
4. What is the frequency range of the electromagnetic spectrum?.
Ans. The electromagnetic spectrum is the range of all type of EM radiation.
Frequency (in Hz)
Radio: 106 - 1010
Microwave: 1010 – 1012
Infrared: 1012 – 1015
Visible: 1015 – 1016
UV: 1016 – 1017
X-Ray: 1017 – 1021
Gamma-Ray: 1021 – 1024
5. What are Metamaterials?
Ans. A negative refractive index material is a metamaterial, is a material engineered to have a property that is not found in naturally occurring materials. They are made from assemblies of multiple elements fashioned from composite materials such as metals or plastics. The materials are usually arranged in repeating patterns, at scales that are smaller than the wavelengths of the phenomena they influence. Metamaterials derive their properties not from the properties of the base materials, but from their newly designed structures. Their precise shape, geometry, size, orientation and arrangement gives them their smart properties capable of manipulating electromagnetic waves: by blocking, absorbing, enhancing, or bending waves, to achieve benefits that go beyond what is possible with conventional materials.
6. Explain the magic tee and transmission line.
Ans. A magic tee is a hybrid or 3 dB couple used in a microwave system. It is an alternative to the rat-race coupler. In contrast to the rat-race, the three dimensional structure of the magic tee makes it less readily constructed in planar technologies such as microstrip or stripline.
A transmission line is a specialized cable or other structure designed to carry alternating current at radio frequency.
7. Which antennas are used in satellites?
Ans. They are:
- Parabolic antenna
- Horn antenna
- Helical antenna
- Phased antenna
8.What is a spot beam?
Ans. A spot beam is a satellite signal that is especially concentrated in power so that it will cover only a limited geographic area on earth and power will be more focused.
9. What is isotropic and Omni-directional antenna and what is the difference?
Ans. An isotropic antenna is an ideal antenna that radiates its power uniformly in all direction. It does not exist physically and is often used as a reference antenna for antenna gain.
An Omni-direction antenna is a wireless antenna that radiates or intercepts electromagnetic field equally well in all horizontal direction in a flat, two dimensional (2d) geometrical plane.
10. What is different between Reflex Klystron and Magnetron amplifiers used in the microwave?
Ans. A magnetron is capable to deliver more power than reflex klystron.
Magnetrons are capable of delivering pulse power of over 100 MW at 10 GHz while reflex klystron can supply only a few watts.
Magnetron has high efficiency and very poor frequency agility.
In reflex klystron, two voltage sources are needed and it produces less noise.
11. What are the functions of an antenna?
Ans. An antenna is an interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver. In transmission, a radio transmitter supplies an electric current to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic waves (radio waves). In reception, an antenna intercepts some of the power of a radio wave in order to produce an electric current at its terminals, that is applied to a receiver to be amplified.
12. What are the advantages of microwaves?
Ans. The advantages of microwaves are :
- Large bandwidth (high-frequency ranges have high bandwidth )
- Better directivity as directivity is proportional to frequency.
- Small size antenna (higher the frequency smaller the size of the antenna)
- Low power consumption
- Effect of fading can be minimized by using a line of sight communication.
13. Explain about satellite communication.
Ans. A communications satellite is an artificial satellite that relays and amplifies radio telecommunications signals via a transponder. it creates a communication channel between a source transmitter and a receiver at different locations on Earth. Communications satellites are used for television, telephone, radio, internet, and military applications, generally satellites are in geostationary orbit 22,200 miles (35,700 km) above the equator, so that the satellite appears stationary at the same point in the sky, so the satellite dish antennas of ground stations can be aimed permanently at that spot and do not have to move to track it.
The high-frequency radio waves used for telecommunications links travel by line of sight and so are obstructed by the curve of the Earth. The purpose of communications satellites is to relay the signal around the curve of the Earth allowing communication between widely separated geographical points. Communications satellites use a wide range of radio and microwave frequencies.
14. What is the frequency range of microwave frequency, optical frequency?
Ans.
Radiofrequency ⇒ 3 MHz-300 MHz
Microwave frequency ⇒ 1 GHz – 300 GHz
Optical frequency ⇒ 3 THz-3000 THz
15. Explain the working of a microwave oven.
Ans. A microwave generator called magnetron taken electricity from the power outlet and convert into high powered radio waves. These enter the food compartment through a waveguide. These microwaves penetrate inside the food and make the molecules inside them to vibrate creating heat, thus the food inside the oven is heated by the dielectric heating phenomenon.
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