Microwave Engineering

Text Books:

1. Microwave Devices and Circuits – Samuel Y. Liao

2.Microwave and Radar Engineering- M.Kulkarni

Reference:

1.Microwave Engineering by David M.Pozar

2.Understanding microwaves by Allan W.scott
Evaluation scheme

CWS: 15 Marks

1.3 assignments each of 5 marks =2X5=10 Marks - Normalized to 5 Marks

2.1 Quiz MCQ =10 Marks (overall syllabus)=10 marks-Normalized to 5 Marks
3.Attendance =5 Marks

MTE : 20 Marks

ETE : 40 Marks

PRS: 25 Marks

1. Lab file: 10 marks

2. Quiz based on experiments performed during lab:10marks
3. Day to day evaluation plus attendance :5 Marks
 Introduction

 The Electric field is produced by stationary electric charges, and the magnetic field is
produced by moving electric charges

Magnetic Fields
Electric Fields
 A time varying magnetic field produces an electric field and vice versa. These electric
and magnetic fields are represented by Maxwell’s equations.

Differential form
Integral form

The constitutive relations

The solutions of Maxwell’s equations are electromagnetic waves in which electric
and magnetic fields travel together through space at the speed of light

Electromagnetic Wave
 Characteristics of Electromagnetic Waves

Characteristics of electromagnetic waves are frequency, wavelength, impedance,

power density and phase.

Frequency

Frequency is defined as the number of oscillations that an electrical signal

completes in one second
 Wavelength

Wavelength is defined as the distance in which the fields of an electromagnetic wave repeat
themselves
RF and microwave frequency bands
 IEEE Frequency Band Designations

 The Institute of Electrical and Electronics Engineers (IEEE) recommended microwave

frequency band designations, which are given in Table
ADVANTAGES OF MICROWAVES

 Large Bandwidth:
The Bandwidth of Microwaves is larger than the common low frequency radio
waves. Thus more information can be transmitted using Micro waves. It is very
good advantage, because of this, Microwaves are used for Point to Point
Communications
Ex: FM 98.3 MHz
Lowest frequency 98.29 MHz Highest Frequency 98.31 MHz Then Band width is
0.02 MHz i.e 20 KHz so we can transmit /receive music /10-15 audio
Now let us consider microwave frequency Ex. Bluetooth 2.4 GHz
Lowest frequency 2.399 GHz Highest Frequency 2.41 gHz Then Band width is 0.02
GHz i.e 20 MHz so we can transmit /receive 1000 audio or video channels
 Better Directivity:
At Microwave Frequencies, there are better directive properties. This is due to the
relation that As Frequency Increases, Wavelength decreases and as Wavelength
decreases Directivity Increases and Beam width decreases. So it is easier to design and
fabricate high gain antenna in Microwaves

Ex: Parabolic antenna

Beam width=140 λ/D
Where D is diameter of an antenna, λ is wave length
Directivity is inversely proportional to the Beam width and Gain is directly proportional
to Directivity
 Small Size Antenna:
Microwaves allows to decrease the size of antenna. The antenna size can be smaller
as the size of antenna is inversely proportional to the transmitted frequency. Thus in
Microwaves, we have waves of much higher frequencies and hence the higher the
frequency, the smaller the size of antenna.

As aperture area=λ2 D/4π

Where D is directivity of an antenna
 Low Power Consumption:
The power required to transmit a high frequency signal is lesser than the power
required in transmission of low frequency signals. As Microwaves have high
frequency thus requires very less power

 Effect Of Fading:
The effect of fading is minimized by using Line Of Sight propagation technique at
Microwave Frequencies.
While at low frequency signals, the layers around the earth causes fading of the
signal
 APPLICATIONS OF MICROWAVES
 There are many Industrial, Scientific, Medical and Domestic Applications of
Microwaves.
The great example of Application of Microwaves is‘ Microwave Oven‘ which we uses
in our daily life.
Following are the other main application areas of Microwaves:
Communication
Remote Sensing
Heating
Medical Science
 Communication: Microwave is used in broadcasting and telecommunication
transmissions.
 As described above, they have shorter wavelengths and allows to use smaller
antennas. The cellular networks like GSM, also uses Microwave frequencies of
range1.8to1.9GHz for communication.
 Microwaves are also used for transmitting and receiving a signal from earth to
satellite and from satellite to earth.
 Military or Army also makes use of Microwaves in their communication system.
They uses X or Ku band for their communication
 Remote Sensing: Most of you may be familiar with this Application. The most
common application of Microwave is its use in RADAR and SONAR.
RADAR is used to illuminate an object by using a transmitter and receiver to
detect its position and velocity. Radiometry is also one of the Remote Sensing
Applications.
 Heating:
We uses Microwave Oven to bake and cook food. It is very convenient electronic
machine which performs the heating task very cleanly and in a very less time.
There are also some other applications of heating property of microwave such as
Drying, Precooking and Moisture Levelling.

 Medical Science:
Microwave's heating properties are also used in Medical Science.
Microwave also have Medical Applications such as it is used in diagnosis and various
therapies.
Why microwave devices are needed
Scattering Matrix:

Usually we use Z,Y,H or ABCD parameters to describe a linear two port network.

These parameters require us to open or short a network to find parameters.

At Radio frequencies it is difficult have a proper short or open circuit there are parasitic
inductance and capacitance in most instances
 Open/short conditions leads to standing wave can cause oscillation and
destruction of device
 For Non-TEM propagation mode it is not possible to measure voltage (or) current
so we can only measure Electric Field(E) and Magnetic Field(H)
 Hence we set of parameters scattering(S) is
Do not need open/short conditions
Do not cause standing wave
Relates to incident and reflected power waves instead of voltage and
current
MICROWAVE COMPONENTS
 The waveguide corner, bend, and twist are shown in figure below, these
waveguide components are normally used to change the direction of the guide
through an arbitrary angle.
 WAVE GUIDE TEE JUNCTIONS:

E plane Tee
H plane Tee

Magic Tee
Directional Coupler:
A Directional coupler is a device that samples a small amount of Microwave power
for measurement purposes. The power measurements include incident power,
reflected power, VSWR values, etc.
Directional Coupler is a 4-port waveguide junction consisting of a primary main
waveguide and a secondary auxiliary waveguide
Directional coupler is used to couple the Microwave power which may be
unidirectional or bi-directional
 Circulators and isolator : Non reciprocal transmission devices uses the property of
faraday rotation in the ferrite material

Phase shifters:

A microwave phase shifter is a two port device which produces a variable shift in
phase of the incoming microwave signal. A lossless dielectric slab when placed inside
the rectangular waveguide produces a phase shift
 Insertion loss, Gain and return loss

Actually there is a mismatch between the microwave field configuration in the

transmission line and in the component.

These two quantities completely describes the performance of the component

Microwave Tubes: Two types
1.Linear Beam tube 2.Cross field tube
 These are linear beam tubes, i.e. the magnetic field is in parallel with the DC
electric field
Crossed Field Tubes

These are cross field devices i.e. the d.c. magnetic field and the d.c. electric field are
perpendicular to each other.
Microwave semiconductor devices
 Micro wave solid state devices such as tunnel diodes, Gunn diodes, Transfer
electronic devices and avalanche transit time device
 The common characteristic of all active two-terminal solid-state devices is
their negative resistance
 Transistors operate with either junctions or gates, but TED es bulk devices
having no junctions or gates.
 The majority of transistors are fabricated from elemental semiconductors,
such as silicon or germanium, whereas TED are fabricated from compound
semiconductors, such as gallium arsenide (Ga.As),indium phosphide (lnP), or
cadmium telluride (CdTe)
Thank you