Microwave communication is a transmission of signals by sending microwaves. Microwaves are radio signals with a very short wavelength .Microwave frequency ranges from 1GHZ to 300GHZ . Microwaves is used to communicate with geostationary satellites as microwaves have small wavelength and high frequency It is a line-of-sight wireless communication technology that uses high frequency beams of radio waves to provide high speed wireless connections that can send and receive video, voice, data information.
It is a communications system that uses a beam of radio waves in the microwave frequency range to transmit video, audio, or data between two locations, which can be from few meters to several kilometers
MICROWAVE COMMUNICATION TYPES:
- Terrestrial microwave transmission
- Satellite microwave transmission
Terrestrial microwave transmission:
This system uses directional parabolic antennas to transmit and receive signals in the lower gigahertz range and the frequency range is from 4 GHZ to 6 GHZ .this provides bandwidth from 1 to 10Mbps
Line of sight requirements makes difficult for installation and can be used for short distance systems as it is inexpensive.
Satellite microwave transmission :
This system uses satellites for sending and receiving signals .this system needs satellites in the geostationary orbit which is 36000 km above the earth .The frequency range used in this system is between 11 GHZ to 14 GHZ .it requires proper alignment of earth station antennas .this system is very expensive and it covers a vast area .
Microwaves travel in straight line so transmitter and receiver stations should be in line of sight .Since microwave is unidirectional ,it allows multiple receivers to receive the signal without interference .
Microwave frequency bands
Microwave signals is divided into three frequency bands :
Ultra high frequency (UHF) (0.3-3 GHz)
super high frequency (SHF) (3-30 GHz)
extremely high frequency (EHF) (30-300 GHz)
Microwave transmission is carried using the microwave antennas which uses either of the following radio bands:
- L band 1 to 2 GHz
- S band 2 to 4 GHz
- C band 4 to 8 GHz
- X band 8 to 12 GHz
- Ku band 12 to 18 GHz
- K band 18 to 26.5 GHz
- Ka band 26.5 to 40 GHz
- Q band 30 to 50 GHz
- U band 40 to 60 GHz
- V band 50 to 75 GHz
- E band 60 to 90 GHz
- W band 75 to 110 GHz
- F band 90 to 140 GHz
- D band 110 to 170 GHz
It needs unidirectional antennas to send out signals. Examples are parabolic dish antenna and Horn antenna.
Parabolic dish Antenna :
In receiving station a parabolic dish antenna is used because of its directivity and high gain and it has a curved surface with the cross sectional shape as parabola and it has high SNR
Horn Antenna :
It has a flaring metal shaped waveguide shaped like a horn to direct radio waves in a beam .waveguide is used to transmit and receive signals
Microwave signals are propagated through waveguides in order to minimize the losses. A microwave waveguide with a single conductor is a high pass filter and it is a hollow metallic tube of uniform cross section for transmitting electromagnetic waves by successive reflections from the inner conducting layered wall of tube .waveguides are used to couple transmitter power to antenna and microwave signal from antenna to receiver and it’s dimension determines the operating frequency range
MICROWAVE PROPAGATION :
Microwave signal travel along a straight line path Microwave signal bend slightly when passing through different layers of air density and the atmospheric condition that cause optical mirages can cause microwave fading problem . Radar signals at microwave frequencies can be used to track ships even at distance of hundred miles .microwaves are reflected by flat surfaces .flat reflectors are usually placed at top of tall microwave -relay towers .
Fresnel zone :
It is the elliptical area around the LOS between the sender and Receiver. Microwaves spread into this area are generated by an antenna and this area should be free from obstacles the first Fresnel zone is the region where the microwave transmission energy is concentrated and with increase in Fresnel zone serial numbers the field strength of the receiving point reduces as per arithmetic series
FADING IN MICROWAVE PROPAGATION :
Fading is a deviation or attenuation that a signal experiences over a propagation media.fading may either due to multipath propagation (signals reaching the receiving antenna by two or more paths),weather (rain),shadowing from obstacles after the propagation of the wave .
APPLICATION OF MICROWAVE IN COMMUNICATION:
- Wireless LAN protocols, such as Bluetooth and the IEEE 802.11 specifications of Wi-Fi, use microwaves in the 2.4 GHz ISM band
- Most satellite communications systems operate in the C, X, Ka, or Ku bands of the microwave spectrum .Satellite TV either operates in the C band for the traditional large dish fixed satellite service or Ku band for direct-broadcast satellite. Military communications run primarily over X or Ku-band links, with Ka band being used for Milstar