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1.3. Need of Microwave frequencies:
The following properties of microwave made it important and its need for various applications:
• Large Bandwidth: The Bandwidth of Microwaves is larger than the common low frequency radio waves. Thus more information can be transmitted using Microwaves. It is very good advantage, because of this, Microwaves is used for Point to Point Communications.

• Improved Directivity: Microwaves are the waves with higher frequency. Therefore when frequency increases, wavelength decreases and when wavelength decreases directivity increases and beam width decreases there are better directive properties at microwave frequencies. Therefore it is very simple to propose and construct high gain antenna in Microwaves.

• Small Size Antenna: In Microwaves, it is possible to use the antenna having small size. The size of the antenna can be smaller since the size of antenna is inversely proportional to the transmitted frequency. Therefore in Microwaves, we have waves of much high frequencies and that’s why the higher the frequency, the smaller the size of antenna.

• Low Power Consumption: The power required to transmit a low frequency signal is more than the power required in transmission of high frequency signals. A microwave requires very less power because of its high frequency.

• Effect of Fading: Effect of fading can be minimized by using microwave frequencies. It is possible by using Line Of Sight propagation technique. At the same time, at low frequency signals, the layers around the earth cause fading of the signal.

1.4. RF ; Microwave spectrum (region and bands)
The microwave spectrum is usually defined as electromagnetic energy ranging from approximately 1 GHz to 100 GHz in frequency. Microwave region bands in the electromagnetic spectrum along with other frequency ranges are as follows. These standard band distributions of frequency are according to Institute of Electrical Engineering (IEEE).The band distributions acoording to IEEE is given in the below Table.
Band Designations Frequency Range(GHz)
UHF 0.3 to 3.0
L 1.1 to 1.7
LS 1.7 to 2.6
S 2.6 to 3.9
C 3.9 to 8.0
X 8.0 to 12.5
Ku 12.5 to 18.0
K 18 to 26
Ka 26 to 40
Q,U,M,E,F,G,R(Millimeter) 33 to 300
Submillimeter ;330

Frequency ; Wavelength Range with Applications of various bands
Band Designation Wavelength Range Frequency range Applications
ELF band
10 to 1 mm 30-300 Hz Communication with submarines
VLF band
100 to 10 km 3 to 30 KHz Point to point communication at long distance
LF band 10 to 1 km 30 to 300 KHz Point to point marine communication
MF band
1000 to 100 m 300 to 3000 kHz Marine communication and broadcasting
HF band
100 to 10 m 3 to 30 MHz Medium and long distance communication
VHF band
10 to 1 m 30 to 300 MHz FM and Television service, aviation and police
UHF band
100 to 10 cm 300 to 3000 MHz Short distance communication
SHF band
10 to 1 cm 3 to 30 GHz Space communication Radar and microwave
EHF band
10 to 1 cm 30 to 300 Hz Space communication Radar and microwave

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