Introduction of Microwave.pdf

8/9/2019 Introduction of Microwave.pdf

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1.1 Introduction to Electromagnetic Spectrum

The term “Spectrum” was first introduced in the 17th century to explain

the range of colours observed when white light is passed through a prism.

It was soon applied to other waves like sound waves, electromagnetic

waves etc.

Now it is applied to any signal that can be decomposed into frequency

components.

“EM Spectrum” refers the range of all possible frequencies of EM

radiations and it extends from low frequencies, used for Radio

Communication to higher end at Gama radiation. Alternatively it covers

wavelengths from thousands of km down to the fraction of the size of an

atom.



The term “Microwave” usually refers to that part of the EM spectrum which

is covered by wavelength range 1m to 1 cm or in frequency scale 300 MHz to30 GHz.

Above this frequency the wavelength becomes of the order of mm and is

called “Millimetre Wave” (30 GHz to 300 GHz).

The term “Micro” in the “Microwave” stands for “Extremely small in scale”

and it includes both the microwave and millimetre wave spectrum i.e., UHF,

SHF and EHF bands.



Frequency Band Designations Typical Applications

3 kHz – 30 kHz Very Low Frequency(VLF)

Navigation & Sonar.

30 kHz – 300 kHz Low Frequency (LF) Radio beacons & Navigation.

300 kHz – 3 MHz Medium Frequency (MF) AM broadcasting & Coast guardcommunication

3 MHz – 30 MHz High Frequency (HF) Telephone, Telegraph, FAX, Ship

to coast and ship to aircraft

communication, Shortwave

international broadcasting,

Amateur radio and Citizen’s band.

30 MHz – 300 MHz Very High Frequency

(VHF)

Air traffic control, Police,

Television, FM, Taxicab mobile

radio and Navigational aids.

Table 1.1: Electromagnetic Frequency Band Designation



Frequency Band Designations Typical Applications

300 MHz – 3 GHz Ultra High Frequency

(UHF)

Satellite communication,

Surveillance RADAR, Mobile

communication, Television and

navigational aids.

3 GHz – 30 GHz Super High Frequency

(SHF)

Airborne RADAR, Microwave

communication, Mobile

communication and Satellite

communication.

30 GHz – 300 GHz Extreme High

Frequency (EHF)

RADAR

300 GHz – 6 THz Far Infra-Red (FIR) Terahertz time domain

spectroscopy, Terahertz imaging

6 THz – 100 THz Mid Infra-Red (MIR) Guided missile and Thermal

imaging



Frequency

Band

Designations Typical Applications

100 THz – 400

THz

Near Infra-Red (NIR) Fibre optic telecommunication, Night

vision, Long distance telecommunication

400 THz – 750

THz

Visible Light Optical communication

750 THz – 1PHz Near Ultra Violet(NUV)

Optical sensors, UV-ID, Label tracking,

Barcode, Forensic analysis, Drugdetection, Protein analysis, DNA

sequencing, Drug discovery, Medical

imaging of cells, Solid state lighting,

Curing of polymers and printer inks,

Light therapy in medicine and Bug

zappers.



Frequency

Band

Designations Typical Applications

1 PHz – 30 PHz Extreme Ultra Violet

(EUV)

Extreme ultra violet lithography, Optical

sensors, Disinfection, Decontamination

of surface and water, UV-ID, Label

tracking, Barcode, Protein analysis,

DNA sequencing and Drug discovery.

30 PHz – 3 EHz Soft X-Ray (SX)

X-Ray microscopic analysis, X-Ray

crystallography, Medical imaging ofbones, Airport security, Border control,

Astronomy.

3 EHz – 30 EHz Hard X-Ray (HX) Absorption spectroscopy, Scanning

microprobe and Radiotherapy.

> 30 EHz Gamma Rays ( - Ray) Container security initiative, Irradiation,

Gamma-knife surgery and Nuclear

medicine.

g



Table 1.2: Letter designation of Microwave bands as per as per Radio

Society of Great Britain

Frequency Bands Frequency Range (GHz)

L 1 – 2

S 2 – 4

C 4 – 8

X 8 – 12

Ku 12 – 18

K 18 – 26.5Ka 26.5 – 40

Q 33 – 50

U 40 – 60

V 50 – 75

E 60 – 90

W 75 – 110F 90 – 140

D 110 – 170

G 140 – 220

H 170 – 260



Table 1.3: Letter designation of microwave bands as per US Navy and

International Telecommunication Union (ITU)

Band US Navy ITU

L 0.390 – 1.55 1.215 – 1.400

S 1.55 – 3.90 2.300 – 2.500

2.700 – 3.700

C 3.90 – 6.20 5.250 – 5.925

X 6.20 – 10.90 8.500 – 10.680

Ku 15.25 – 17.25 13.40 – 14.0015.70 – 17.70

K 10.90 – 36.00 24.05 – 24.25

24.65 – 24.75

Ka 33.00 – 36.00 33.40 – 36.00

Q 36.00 – 46.00

V 46.00 – 56.00 59.00 – 64.00W 56.00 – 100.00 76.00 – 81.00

92.00 – 100.00



1.2 Characteristics Features of Microwave

Upto around a frequency of 1 GHz, most circuits are designed andconstructed using lumped parameter circuit components.

Above 1 GHz the propagation time of the signal becomes comparable

with the time period of the signal. The lumped parameter circuit

component length also becomes comparable to the wavelength.This results in a rapid amplitude and phase variation of the signal

with the distance.

The phase difference caused by the interconnection of different

components is also not negligible above 1 GHz.

As a result at high frequencies KCL, KVL and normal voltage –

current concepts are not applicable. Instead field theory is required.

Limitations:



Above 1 GHz the lumped circuit elements are replaced by the

distributed circuit element.

The distributed circuit elements are small transmission line sections

and the are defined over an infinitesimal length.

In this model the connecting wires between different elements are not

perfect conductor.

At high frequencies the distributed circuit model is more accurate

than the lumped element circuit model and also more complex in nature.

The existence of non-uniform current in the branches and non-uniform

voltages at the nodes further complicates the analysis of the circuit.The use of infinitesimals in distributed circuit model requires the

application of calculus rather than linear algebra.

Distributed circuit theory



The high frequency nature of microwave has also brought the

complexity and challenges in designing microwave active components.

At microwave frequencies the transit time of the carriers through

ordinary low frequency triode and transistors becomes comparable with

the time period of the wave which restricts its operation at these

frequencies.

A number of new principles of operation namely velocity modulation,

interaction of space charge waves with EM field, quantum mechanical

tunnelling, avalanche breakdown and transferred electron techniques etc.

have been employed to generate microwave signals.

Challenges in designing microwave sources



At microwave frequencies measurements of voltages and currents are

not possible with a multimeter or any other low frequency circuits.

At microwave frequencies the impedance of the parasitic of the

measurement cables and connectors become large enough and frequently

cross the component values. Thus special cable and connectors are

required.

The meter impedance and capacitance also affect the measurement.

The most common method to do microwave measurement is to measure

the field amplitudes, phase difference and power carried by the waves.

Another very common used method is based on the standing wave

pattern measurement.

Challenges in measurement



1.3 Advantages of Microwave

High bandwidth

Improved gain / directive propertiesReduction in antenna size

Low power requirement

Fading effect and reliability

Transparency property of microwave

1.4 Disadvantages of Microwave

Line of sight propagationSubject to electromagnetic interference

Affected by bad weather

Costly equipments



1.3 Applications of Microwave

Radio detection and ranging

Terrestrial microwave link

Transmission of many television channels over one link

Satellite communication

Radio astronomyLinear particle accelerator

Studies on basic properties of materials

Microwave oven

Industry

Medical Science

Documents

Introduction of Microwave.pdf