# Introduction to Microwaves Engineering

Updated on 2017/08/09 16:42

## Syllabus

• Introduction to Microwaves engineering: History of Microwaves, Microwave Frequency Bands

## Introduction

### Definition and Equation

Definition: Micro-waves are Electromagnetic waves whose frequencies range from 1GHz to 1000GHz.

$\lambda =\frac{c}{f}$
where,
λ = wavelength,
c = velocity of light = $3\times 10^{8}m/s$,
= frequency (For  f=1Ghz and For f =1000Ghz i.e. µ - wave frequencies has wavelength in the range of few tens of cm to a fraction of mm.)

### Microwave Properties

• Microwaves frequency range 1 GHz – 300 GHz
• Microwave is an electromagnetic radiation of short wavelength.
• Reflected by conducting surfaces
• Microwave currents flow through a thin outer layer of an ordinary cable.
• They are not reflected by ionosphere

## Microwave Region & Band Designations

### Electromagnetic frequency spectrum

 Electromagnetic Spectrum Frequency Range ELF 30Ghz-300Hz SLF 300hz-3KHz VLF 3Khz-30KHz LF 30Khz-300KHz MF 300Khz-3MHz HF 3Mhz-30MHz VHF 30Mhz-300MHz UHF 300Mhz-3GHz SHF 3GHz-30GHz EHF 30Ghz-300GHz Infra red 300GHz-430THz Light 430THz-1000THz X-rays 1000THz-1018Hz

### Microwave Frequency Bands Designation

 Band Frequency (GHz) Wavelength(cm) L 1 to 2 30.0 to 15.0 S 2 to 4 15 to 7.5 C 4 to 8 7.5 to 3.8 X 8 to 12 3.8 to 2.5 Ku 12 to 18 2.5 to 1.7 K 18 to 27 1.7 to 1.1 Ka 27 to 40 1.1 to 0.75 Millimeter 40-300 0.75-0.1

1. Increased bandwidth availability: µ-waves have large bandwidth (1GHz-10.3GHz)
Advantage of large bandwidth is that the frequency range of information channel will be a small percentage of the carrier frequency & more information can be transmitted in a µ -wave frequency range.
Actually µ-wave region (1000GHz) contains 1000 sections of the frequency band 0-10̂̂9  &  hence any one of these  thousand sections may be used to the transmit all the TV, radio & others communication.
( bandwidth speech 4Kha, Music 10-15KHz,TV=5-7MHz )
2. Improved directive Properties: As frequency ↑, directivity ↑  &  Beam width↓ Hence the bandwidth of radiations Ɵ is proportional.
• Power radiated: P= µ0 ∏2. I0 ̂2(L/ ʎ)2
Gain= µ0. ∏2, L= length, I0= ac current carried

As the frequency ↑ , ʎ ↓ hence power radiated & gain↑ & directive antenna can be designed & fabricated more easily at   µ-wave frequency which is impracticable at low frequency  bands.
3. At µ-wave frequency antenna size of several wavelengths lead to smaller beam-width & an extremely directive beam.
e.g for parabolic antenna β=140/ (D/ʎ ), where D= diameter of antenna in centimeter, ʎ= Wavelength in centimeter, β=Beam width in degree
At 30GHz (ʎ=1cm) for 1degree beam width, D=140/B  X  ʎ = 140/1X10=140cm
At 300MHz (ʎ = 100cm) for 1degree beam width, D=140/1X100cm = 140cm
Hence it is clear that antenna size is small for µ-wave frequencies
4. Fading effect & Reliability: Fading effect due to variation in the transmission modem is more effective at low frequency. Due to line of sight (LOS) propagation & high frequency there is less fading effect & hence µ-wave communication is more reliable.
5. Power Requirements: Very Low
6. Transparency property of µ-wave frequency band ranging from 300MHz-10GHz are capable of freely propagating thought ionized layers, surrounding the earth as well as thought atmosphere.

## References

• WikiNote Foundation
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Created by Vishal E on 2017/07/22 17:58

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