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 SpectrumFrequency 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

Advantages of Microwaves

  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