Microwaves have wavelengths between 1 mm and 1 m, with frequencies between 300 MHz and 300 GHz. They are used widely in technology for communication links, wireless networks, radar, satellite communication, medical devices, cooking, and more. Key developments included Maxwell's electromagnetic theory, Hertz's experiments with antennas and propagation, and modern devices like the microwave oven and Gunn diode. Mismatch losses that occur when transmitting microwaves include attenuation, reflection, transmission, return, and insertion losses.

1. Microwave and
Antenna (18EC72)
By
KAVITHA DEVI CS
Assistant Professor
Dept. of ECE, Dr.AIT, Bangalore-56

2. Introduction:
Electromagnetic Spectrum
Microwave is a form
of electromagnetic
radiation with wavele
ngths ranging from
about one meter to
one millimeter
corresponding freque
ncies between
300MHz and 300GHz
respectively
A more common
definition in radio-
frequency
engineering is the
range between 1GHz
and100GHz
(wavelengths between
0.3 m and 3 mm).

3. Applications:
Microwaves are widely used in modern technology, for example in
point-to-point communication links,
wireless networks,
microwave radio relay networks,
radar,
satellite and spacecraft communication,
medical diathermy and cancer treatment,
remote sensing,
radio astronomy,
particle accelerators,
spectroscopy,
industrial heating,
collision avoidance systems,
garage door openers and keyless entry systems, and
for cooking food in microwave ovens.

4. Guglielmo Marconi
• inventor and electrical engineer, known for his creation of a
practical radio wave-based wireless telegraph system. This led
to Marconi being credited as the inventor of radio and in
1909 Nobel Prize in Physics

5. Marconi'sfirsttransmitterincorporatingamonopoleantenna

6. Types of Antennas

19. History of Microwaves
1. James C Maxewll, the founder of electromagnetic theory of
radiation presented in 1864 it describes the properties of EM
fields in terms of 20 equations known as Maxwell's equations.
2. In 1893, Heinrich Hertz first conducted an experiment to
show a parabolic antenna fed by dipole. He also gave a strong
experimental support for a theoretical conclusions drawn by
Maxwell for electromagnetic fields
3. In 1893 William Thompson developed the waveguide theory
for propagation of microwaves in a guided structure.
4. In 1897 – 1899 Lodge established the mode properties of
propagation of EM waves in free space & in hallow metallic
tube known as waveguide

20. History of Microwaves
5. In 1895 - 98 Sir J. C Bose generated millimeter waves using
circuits useful for communications. And developed microwave
spectrometer, Polari meters and detectors for conducting
microwave experiments. He also developed microwave horn
antennas which are still considered to be useful feeds for
reflector antenna.
6. In 1937, Russel & Varian Bross developed microwave vaccum
tube klystron
7. In 1938 J.D Kraus developed corner reflector antenna for EM
wave transmission.

21. History of Microwaves
8. In 1944 Kompfner developed the microwave travelling wave tube.
9. In 1946 Percy Spencer built the microwave oven for domestic cooking.
10. After 1950 some of the modern devices were developed.
11. In 1953 Deschamps developed the microstrip antenna.
12. In 1963 J.B Gunn developed the Gunn diode for microwave
generation using solid state materials such as GaAs
And there are many more numerous events, research and developments
in the field of microwaves

22. Mismatch Losses in Transmission Lines
Due to mismatch between the input and output terminations of
a lossy transmission lines, 5 losses are often defined in
microwave circuits. These are 1. Attenuation loss
2. Reflection loss
3. Transmission loss
4. Return loss
5. Insertion loss

23. Mismatch Losses in Transmission Lines
1. Attenuation loss : The attenuation loss is a measure of
the power loss due to signal absorption in the line or
device
Attenuation loss (dB) = 10 log 𝐼𝑛𝑝𝑢𝑡 𝑒𝑛𝑒𝑟𝑔𝑦 −𝑅𝑒𝑓𝑙𝑒𝑐𝑡𝑒𝑑 𝑒𝑛𝑒𝑟𝑔𝑦 𝑎𝑡 𝑡ℎ𝑒 𝑖𝑛𝑝𝑢𝑡
𝑇𝑟𝑎𝑛𝑠𝑚𝑖𝑡𝑡𝑒𝑑 𝑒𝑛𝑒𝑟𝑔𝑦 𝑡𝑜 𝑡ℎ𝑒 𝑙𝑜𝑎𝑑
= 8.686 𝛼𝑙
𝛼 = 𝑎𝑡𝑡𝑒𝑛𝑢𝑎𝑡𝑖𝑜𝑛 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡
𝑙 = 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑡𝑟𝑎𝑛𝑠𝑚𝑖𝑠𝑠𝑖𝑜𝑛 𝑙𝑖𝑛𝑒
(In the line or device)

24. Mismatch Losses in Transmission Lines
2. Reflection Loss: is a measure of power loss during
transmission due to the reflection of the signal as a result of
impedance mismatch.
Reflection loss (dB) = 10 log
𝐼𝑛𝑝𝑢𝑡 𝑒𝑛𝑒𝑟𝑔𝑦
𝐼𝑛𝑝𝑢𝑡 𝑒𝑛𝑒𝑟𝑔𝑦 −𝑅𝑒𝑓𝑙𝑒𝑐𝑡𝑒𝑑 𝑒𝑛𝑒𝑟𝑔𝑦
= 10 log
1
1 − 𝐼𝜏𝐼2
𝜏 = 𝑟𝑒𝑓𝑙𝑒𝑐𝑡𝑖𝑜𝑛 coefficient
(at a plane)

25. 3. Transmission Loss: is a measure of loss of power due to
transmission through the line or device.
Transmission loss (dB) = 10 log
𝐼𝑛𝑝𝑢𝑡 𝑒𝑛𝑒𝑟𝑔𝑦
𝑇𝑟𝑎𝑛𝑠𝑚𝑖𝑡𝑡𝑒𝑑 𝑒𝑛𝑒𝑟𝑔𝑦
= Attenuation loss + Reflection loss
= 8.686 𝛼𝑙 + 10 log
1
1 − 𝐼𝜏𝐼2
(due to the line)

26. 4. Return Loss: is a measure of the power reflected by a line or
network or device.
Return loss (dB) = 10 log
𝐼𝑛𝑝𝑢𝑡 𝑒𝑛𝑒𝑟𝑔𝑦 𝑡𝑜 𝑡ℎ𝑒 𝑑𝑒𝑣𝑖𝑐𝑒
𝑅𝑒𝑓𝑙𝑒𝑐𝑡𝑒𝑑 𝑒𝑛𝑒𝑟𝑔𝑦 𝑎𝑡 𝑡ℎ𝑒 𝑖𝑛𝑝𝑢𝑡 𝑜𝑓 𝑡ℎ𝑒 𝑑𝑒𝑣𝑖𝑐𝑒
= -20 log I𝜏I
𝜏 = 𝑟𝑒𝑓𝑙𝑒𝑐𝑡𝑖𝑜𝑛 coefficient

27. 4. Insertion Loss: is a measure of the loss of energy in transmission
through a line or device compared to direct delivery of energy without
the line or device.
Let 𝑃1 be the power received by a load when connected directly to
source without the line or device, and
𝑃2 the power received by the load when the line or the device is
inserted between the source and the load, while the input power is
held constant. Then
Insertion loss (dB) = 10 log
𝑃1
𝑃2
The insertion loss is contributed by:
1. Mismatch loss at the input
2. Attenuation loss through the device
3. Mismatch loss at the output