Microwave engineering pertains to the study and design of microwave circuits, components, and systems operating between 300 MHz and 300 GHz. Some key topics covered in the document include the fundamental principles of microwave engineering, common applications like radar and wireless transmission, properties of microwaves like their ability to support larger bandwidths, and Maxwell's equations which describe how electric and magnetic fields propagate and interact to form electromagnetic waves. During World War II, microwave engineering played an important role in developing radar to detect enemy ships and planes.

1. Microwave Engineering
Presented by
YEASIN NEWAJ
BSc. in Electrical and Electronic Engineering

2. Microwave engineering
Microwave engineering pertains to the study and design of microwave circuits, components, and systems.
Fundamental principles are applied to analysis, design and measurement techniques in this field. The
short wavelengths involved distinguish this discipline from Electronic engineering. This is because there are
different interactions with circuits, transmissions and propagation characteristics at microwave frequencies.
Some theories and devices that pertain to this field are antennas, radar, transmission lines, space based systems
(remote sensing), measurements, microwave radiation hazards and safety measures.
During World War II microwave engineering played a significant role in developing radar that could accurately
locate enemy ships and planes with a focused beam of EM radiation. The foundations of this discipline are found
in Maxwell's equations and the work of Heinrich Hertz, William Thomson's waveguide theory, J.C. Bose,
the klystron from Russel and Varian Bross, as well as contributions from Perry Spencer, and others.

3. What are Microwaves?
Microwaves refer to the electromagnetic rays with frequencies between 300MHz and
300GHz in the electromagnetic spectrum.
Microwaves are small when compared with the waves used in radio broadcasting.
Their range is in between the radio waves and infrared waves.
Microwaves travel in straight lines and they will be affected lightly by the troposphere.
They don’t require any medium to travel.
Metals will reflect these waves totally. Non metals such as glass and particles are partially
transparent to these waves.
Microwaves are suitable for wireless transmission of signals of having larger bandwidth.

4. Review of Electromagnetic
Electromagnetic radiation consists of electromagnetic waves, which are
synchronized oscillations of electric and magnetic fields that propagate at the speed of light through
a vacuum.
The oscillations of the two fields are perpendicular to each other and perpendicular to the direction
of energy and wave propagation, forming a transverse wave.

5. General Properties of all electromagnetic radiation:
Electromagnetic radiation can travel through empty space. Most other types of waves must travel through some sort of substance.
For example, sound waves need either a gas, solid, or liquid to pass through in order to be heard.
The speed of light is always a constant.
Wavelengths are measured between the distances of either crests or troughs. It is usually characterized by the Greek symbol λ.
 Electromagnetic radiation is a form of energy that is produced by
oscillating electric and magnetic disturbance, or by the movement of
electrically charged particles traveling through a vacuum or matter.
 Electron radiation is released as photons, which are bundles of light
energy that travel at the speed of light as quantized harmonic waves.
 This energy is then grouped into categories based on its wavelength
into the electromagnetic spectrum. These electric and magnetic waves
travel perpendicular to each other and have certain characteristics,
including amplitude, wavelength, and frequency.
Review of Electromagnetic

6. Electromagnetic Spectrum

7. Microwaves Frequency Range

8. Properties of Microwaves/Microwave Circuits
Microwaves are the waves that radiate electromagnetic energy with shorter wavelength.
Microwaves are not reflected by Ionosphere.
Microwaves travel in a straight line and are reflected by the conducting surfaces.
Microwaves are easily attenuated within shorter distances.
Microwave currents can flow through a thin layer of a cable.
Antenna gain is proportional to the electrical size of the antenna. At higher frequencies, more antenna gain
can be obtained for a given physical antenna size, and this has important consequences when implementing
microwave systems.
More bandwidth (directly related to data rate) can be realized at higher frequencies. A 1% bandwidth at 600
MHz is 6 MHz, which (with binary phase shift keying modulation) can provide a data rate of about 6 Mbps
(megabits per second), while at 60 GHz a 1% bandwidth is 600 MHz, allowing a 600 Mbps data rate.
Various molecular, atomic, and nuclear resonances occur at microwave frequencies, creating a variety of
unique applications in the areas of basic science, remote sensing, medical diagnostics and treatment, and
heating methods.

9. Advantages of Microwaves
Supports larger bandwidth and hence more information is transmitted. For this reason, microwaves are
used for point-to-point communications.
More antenna gain is possible.
Higher data rates are transmitted as the bandwidth is more.
Antenna size gets reduced, as the frequencies are higher.
Low power consumption as the signals are of higher frequencies.
Effect of fading gets reduced by using line of sight propagation.
Provides effective reflection area in the radar systems.
Satellite and terrestrial communications with high capacities are possible.
Low-cost miniature microwave components can be developed.
Effective spectrum usage with wide variety of applications in all available frequency ranges of
operation.

10. Disadvantages of
Microwaves
Cost of equipment or installation cost is high.
They are hefty and occupy more space.
Electromagnetic interference may occur.
Variations in dielectric properties with temperatures may occur.
Inherent inefficiency of electric power.

11. Difficulties to Overcome
Microwave circuits are much more difficult to analyze compared to low frequency circuits. Mainly because of:
Voltage is not well defined if the distance between the two points is not electrically small. At microwave frequencies,
“electrically large” distances may be just a few millimeters ! Moving probe leads around will also affect voltage
measurements.
One must carefully choose lumped elements (L, C, R, diodes, transistors etc.) for use in the microwave region.
Typical low frequency components do not behave as expected.
To “transport” electrical signals from one position to another, one must use special “wires.” It is more common to
speak of “guiding” signals at these frequencies.

12. Applications of Microwaves
 Wireless data networks: Bluetooth, WiFi (IEEE Standard 802.11.a/b/g/n), WiMax (IEEE standard 802.16),
Zigbee
 GPS
 Cellular Network
 RADAR(Radio Detection and Ranging)
 Terrestrial TV and Radio Communication
 Satellite Communication
 Military Applications (SONAR applications ,Air traffic control, Weather forecasting, Navigation of ships
,Minesweeping applications )
 Microwave heating.
Semiconductor Processing Techniques( Reactive ion etching ,Chemical vapor deposition)
Medical Applications (Monitoring heartbeat, Lung water detection, Tumor detection, Regional
hyperthermia, Therapeutic applications Local heating, Angioplasty ,Microwave tomography)
Research Applications ( Atomic resonances ,Nuclear resonances)
Industrial Uses

13. Sources of Electromagnetic Fields

14. Maxwell’s Equations
Every electromagnetic form or radiation - visible light, x-rays, sunlight that heats
the earth, radio waves, television waves, wifi signals, bluetooth signals, cell phone
transmission, and GPS all consist solely of Electric and Magnetic Fields. And
everything you need to know about how they propagate and interact with materials
is completely determined by Maxwell’s Equation.
Maxwell's Equations are a set of 4 complicated equations that describe the world of
electromagnetics. These equations describe how electric and magnetic field
propagate, interact, and how they are influenced by objects.

15. Maxwell’s Equations

16. Maxwell’s Equations

17. Gauss’ Law (Point form)
 Gauss' Law is the first of Maxwell's Equations which dictates how the Electric Field behaves around
electric charges. Gauss' Law can be written in terms of the Electric Flux Density and the Electric Charge
Density as:

18. Interpretation of Gauss' Law
 Gauss' Law states that electric charge acts as sources or sinks for Electric Fields.
 If you use the water analogy again, positive charge gives rise to flow out of a volume - this means
positive electric charge is like a source (a faucet - pumping water into a region). Conversely, negative
charge gives rise to flow into a volume - this means negative charge acts like a sink (fields flow into a
region and terminate on the charge).

19. Gauss’ Law for Magnetic Fields:
The law asserts that the net magnetic flux FB through any closed
Gaussian surface is zero. Here B is the magnetic field.
Ñ·B = 0
Well - it is. But it just so happens that no one has ever found magnetic
charge - not in a laboratory or on the street or on the subway. And
therefore, until this hypothetical magnetic charge is found, we set the
right side of Gauss' Law for Magnetic Fields to zero.

20. Faradays’ Law
 We know that an electric current gives rise to a magnetic field - but thanks to Faraday we also know that a
magnetic field within a loop gives rise to an electric current.
Change of magnetic flux induces an electric
field along a closed loop.

21. Ampere’s Law
 Describes how a magnetic field curls around a time-varying electric field or an electric current flowing in a
conductor.
 Third Maxwell’s equation says that a changing magnetic field produces an electric field. But there is no
clue in fourth Maxwell’s equation whether a changing electric field produces a magnetic field? To
overcome this deficiency, Maxwell’s argued that if a changing magnetic flux can produce an electric field
then by symmetry there must exist a relation in which a changing electric field must produce a changing
magnetic flux.

22. ...lets take a look at charge flowing into a capacitor...
E
...when we derived Ampere’s Law
we assumed constant current...
.. if the loop encloses one
plate of the capacitor..there is a
problem … I = 0
B
Side view:(Surface
is now like a bag:)
E
B
B dl I
   0

23. Maxwell solved this problem
by realizing that....
B E
Inside the capacitor there must
be an induced magnetic field...
How?.

24. Maxwell solved this problem
by realizing that....
B E
x
x x x x
x x x x x
x x
A changing
electric field
induces a
magnetic field
Inside the capacitor there must
be an induced magnetic field...
How?. Inside the capacitor there is a changing E 
E
B

25. Maxwell solved this problem
by realizing that....
B E
x
x x x x
x x x x x
x x
A changing
electric field
induces a
magnetic field
Inside the capacitor there must
be an induced magnetic field...
How?. Inside the capacitor there is a changing E 
where Id is called the
displacement current
B dl
d
dt
I
E
d
   
  
0 0 0
F
E
B

26. Maxwell solved this problem
by realizing that....
B E
B dl I d
dt
E
   
  
0 0 0
F
x
x x x x
x x x x x
x x
A changing
electric field
induces a
magnetic field
Inside the capacitor there must
be an induced magnetic field...
How?. Inside the capacitor there is a changing E 
where Id is called the
displacement current
Therefore, Maxwell’s revision
of Ampere’s Law becomes....
B dl
d
dt
I
E
d
   
  
0 0 0
F
E
B

27. Derivation of Displacement Current
q EA I
dq
dt
d EA
dt
  
 
0 0
( )
For a capacitor, and .
I
d
dt
E
 0
( )
F
Now, the electric flux is given by EA, so: ,
where this current, not being associated with charges, is
called the “Displacement Current”, Id.
Hence:
and: B dl I I
B dl I d
dt
d
E


  
   

  
0
0 0 0
( )
F
I
d
dt
d
E
  
0 0
F

28. B dl
d
dt
E
    
0 0
F E dl
d
dt
B
   
F
Electromagnetic Waves
Faraday’s law: dB/dt electric field
Maxwell’s modification of Ampere’s law
dE/dt magnetic field
These two equations can be solved simultaneously.
The result is:
E(x, t) = EP sin (kx-t)
B(x, t) = BP sin (kx-t) ẑ
ˆ
j

29. B dl
d
dt
E
    
0 0
F
E dl
d
dt
B
   
F
B
E
Special case..PLANE WAVES...
satisfy the wave equation
  
 
A t
sin( )
Maxwell’s Solution
v
 
 
 

2
2 2
2
2
1
x t

 
E E x t j B B x t k
y z
 
( , ) ( , )
dE
dt

dB
dt

Electromagnetic Waves