2. Syllabus
MICROWAVE MEASUREMENTS
Microwave Bench general measurement set up,
Measurement Devices and instrumentation:
Slotted line, VSWR meter, power meter,
spectrum analyzer, Network analyzer,
Measurement of frequency, impedance,
Attenuation, power and dielectric constant,
measurement of VSWR, insertion loss ,EMI /
EMC basics and measurement methods. The
FCC and NTIA licensing process, Multi GBPS
data communication and system requirements
2
3. • Among the Microwave measurement devices, a
setup of Microwave bench, which consists of
Microwave devices has a prominent place.
• This whole setup, with few alternations, is able to
measure many values like guide wavelength, free
space wavelength, cut-off wavelength, impedance,
frequency, VSWR, Klystron characteristics, Gunn
diode characteristics, power measurements, etc.
• The output produced by microwaves, in
determining power is generally of a little value.
• They vary with the position in a transmission line.
• There should be an equipment to measure the
Microwave power, which in general will be a
Microwave bench setup.
3
5. Signal Generator
As the name implies, it generates a microwave signal, in the order
of a few milliwatts.
This uses velocity modulation technique to transfer continuous
wave beam into milliwatt power.
A Gunn diode oscillator or a Reflex Klystron tube could be an
example for this microwave signal generator.
Precision Attenuator
This is the attenuator which selects the desired frequency and
confines the output around 0 to 50db.
This is variable and can be adjusted according to the requirement.
Variable Attenuator
This attenuator sets the amount of attenuation. It can be
understood as a fine adjustment of values, where the readings are
checked against the values of Precision Attenuator.
5
6. Isolator
This removes the signal that is not required to reach the
detector mount.
Isolator allows the signal to pass through the waveguide only
in one direction.
Frequency Meter
This is the device which measures the frequency of the signal.
With this frequency meter, the signal can be adjusted to its
resonance frequency.
It also gives provision to couple the signal to waveguide.
Crystal Detector
A crystal detector probe and crystal detector mount are
indicated in the above figure, where the detector is connected
through a probe to the mount.
This is used to demodulate the signals.
6
8. Slotted Line
• In a microwave transmission line or waveguide, the
electromagnetic field is considered as the sum of incident
wave from the generator and the reflected wave to the
generator.
• The reflections indicate a mismatch or a discontinuity. The
magnitude and phase of the reflected wave depends upon the
amplitude and phase of the reflecting impedance.
• The standing waves obtained are measured to know the
transmission line imperfections which is necessary to have a
knowledge on impedance mismatch for effective
transmission.
• This slotted line helps in measuring the standing wave ratio of
a microwave device.
8
9. Construction of slotted line
• The slotted line consists of a slotted section of a transmission
line, where the measurement has to be done.
• It has a travelling probe carriage, to let the probe get
connected wherever necessary, and the facility for attaching
and detecting the instrument.
• In a waveguide, a slot is made at the center of the broad side,
axially.
• A movable probe connected to a crystal detector is inserted
into the slot of the waveguide.
9
10. Operation of slotted line
• The output of the crystal detector is proportional to the
square of the input voltage applied.
• The movable probe permits convenient and accurate
measurement at its position.
• But, as the probe is moved along, its output is proportional to
the standing wave pattern, which is formed inside the
waveguide.
• A variable attenuator is employed here to obtain accurate
results.
• The output VSWR can be obtained by
Where, V is the output voltage.
10
11. 11
1.Launcher –invites the signal,
2.smaller section of waveguide,
3.Isolator-prevents reflections to the
source,
4.Rotary variable attenuator-for fine
adjustments,
5.Slotted section-To measure the signal,
6.probe depth adjustment,
7.Tuning adjustments-To obtain accuracy
8.Crystal detector-detects the signal,
9.matched load-absorbs the power exited,
10.short circuit-Provision to get replaced by a load,
11. Rotary knob-to adjust while measuring,
12.Vernier gauge-For accurate results
Different parts of slotted line
12. In order to obtain a low frequency modulated signal on an
oscilloscope, a slotted line with a tunable detector is
employed.
A slotted line carriage with a tunable detector can be used to
measure the following.
-VSWR
-Standing wave pattern
-Impedance
-Reflection coefficient
-Return loss
-Frequency of the generator used
12
13. Tunable Detector
The tunable detector is a detector mount which is
used to detect the low frequency square wave
modulated microwave signals.
Figure shows a tunable detector mount.
13
15. • In the field of Microwave engineering, there
occurs many applications.
• Hence, while using different applications, we
often come across the need of measuring
different values such as Power, Attenuation,
Phase shift, VSWR, Impedance, etc. for the
effective usage.
• let us take a look at the different
measurement techniques.
15
16. Measurement of Power
The Microwave Power measured is the average power at
any position in waveguide.
Power measurement can be of three types.
Measurement of Low power
- 0.01mWto10mW0.01mWto10mW
-Example − Bolometric technique
Measurement of Medium power
-10mWto1W10mWto1W
- Example − Calorimeter technique
Measurement of High power
- >10W>10W
Example − Calorimeter Watt meter
16
17. Measurement of Low Power
The measurement of Microwave power around 0.01mW to 10mW,
can be understood as the measurement of low power.
Bolometer is a device which is used for low Microwave power
measurements.
The element used in bolometer could be of positive or negative
temperature coefficient.
For example, a barrater has a positive temperature coefficient
whose resistance increases with the increase in temperature.
Thermistor has negative temperature coefficient whose resistance
decreases with the increase in temperature.
Any of them can be used in the bolometer, but the change in
resistance is proportional to Microwave power applied for
measurement.
This bolometer is used in a bridge of the arms as one so that any
imbalance caused, affects the output.
A typical example of a bridge circuit using a bolometer is as shown
in the following figure.
17
18. The milliammeter here,
gives the value of the
current flowing.
The battery is variable,
which is varied to obtain
balance, when an
imbalance is caused by
the behavior of the
bolometer.
This adjustment which is
made in DC battery
voltage is proportional to
the Microwave power.
The power handling
capacity of this circuit is
limited.
18
19. Measurement of Medium Power
• The measurement of Microwave power around 10mW
to 1W, can be understood as the measurement of
medium power.
• A special load is employed, which usually maintains a
certain value of specific heat.
• The power to be measured, is applied at its input
which proportionally changes the output temperature
of the load that it already maintains.
• The difference in temperature rise, specifies the input
Microwave power to the load.
• The bridge balance technique is used here to get the
output.
• The heat transfer method is used for the measurement
of power, which is a Calorimetric technique.
19
20. Measurement of High Power
The measurement of Microwave power around 10W to
50KW, can be understood as the measurement of high power
The High Microwave power is normally measured by
Calorimetric watt meters, which can be of dry and flow type.
The dry type is named so as it uses a coaxial cable which is
filled with di-electric of high hysteresis loss, whereas the flow
type is named so as it uses water or oil or some liquid which
is a good absorber of microwaves.
The change in temperature of the liquid before and after
entering the load, is taken for the calibration of values.
The limitations in this method are like flow determination,
calibration and thermal inertia, etc.
20
21. VSWR meter
The standing wave ratio meter, SWR meter, ISWR
meter (current "I" SWR), or VSWR meter (voltage
SWR) measures the standing wave ratio (SWR) in
a transmission line
The meter indirectly measures the degree of
mismatch between a transmission line and its
load (usually an antenna).
Electronics technicians use it to adjust radio
transmitters and their antennas and feed lines to
be impedance matched so they work together
properly, and evaluate the effectiveness of other
impedance matching efforts.
21
22. SWR meter helps to determine how much of
radiofrequency energy is reflected back to the
transmitter compared to the amount of RF energy
that is been sent out during operation.
This ratio should not be high and the ideal rating is
1:1 such that the power reached the destination and
reflects no power.
The meter that is used to measure SWR is known as
SWR meter.
ISWR meter can measure current SWR and VSWR can
measure voltage SWR.
22
23. The ratio of the maximum radio-frequency
voltage to the minimum radio frequency
voltage along the transmission line is known
as Standing Wave Ratio (SWR).
When SWR is recognized in terms of maximum
and minimum AC voltage along the
transmission lines, it is known as voltage
SWR.
The ratio of the maximum RF current to the
minimum RF current on the transmission line
is known as current SWR.
23
24. Standing waves are known as stationary waves in
physics. Such waves oscillate in time, but the
amplitude does not move. Amplitude remains
constant with time.
In microwave engineering and telecommunications,
the measure of impedance matching of loads to the
impedance of a transmission line is known as SWR.
When there is a mismatch in the impedance, it
results in standing waves along the transmission line,
which increases the transmission line losses.
SWR is generally used to measure the efficiency of a
communication line. This line can include other
cables that allow radio frequency signals and TV
cable signals.
24
28. Directional SWR meter
• A directional SWR meter
measures the magnitude of
the forward and reflected
waves by sensing each one
individually, with directional
couplers.
• A calculation then produces
the SWR.
• Referring to the diagram,
the transmitter (TX) and
antenna (ANT) terminals
connect via an internal
transmission line
28
29. This main line is electromagnetically
coupled to two smaller sense lines
(directional couplers).
These are terminated with resistors at
one end and diode rectifiers at the
other.
The resistors match the
characteristic impedance of the sense
lines.
The diodes convert the magnitudes of
the forward and reverse waves to the
terminals FWD and REV, respectively,
as DC voltages, which are smoothed by
the capacitors.
It will be seen that the configuration of
the two couplers is subtly different -
one has the resistor at one end,
whereas the other has the resistor at
the other. This is to enable the power
in different directions to be monitored.
29
30. 30
The three parallel coupled lines are visible.
Diodes, Capacitors and termination resistors
are mounted at the ends of the sense lines.
Interior view of an SWR meter
31. The SWR bridge uses very few components
Resistors: The two resistors R are chosen to provide
the required load for the bridge element of the
coupler.
Diodes: These are small signal types. Germanium or
Schottky diodes are best as they have a small turn on
voltage and are suitable for small signals.
Meter: The absolute value is not defined, but it must
have a suitably high sensitivity. Meters with 100µA full
scale deflection are what is normally used.
Directional coupler lines: There are several ways of
creating the coupler lines. The most common way is
probably to use a printed circuit board and to run the
main match 50Ω line on the PCB with a ground plane
on the other side.
31
32. SWR Bridge Circuit
SWR can also be measured using an impedance bridge.
The bridge is balanced (0 Volts across the detector) only
when the test impedance exactly matches the reference
impedance.
When a transmission line is mismatched (SWR > 1:1), its
input impedance deviates from its characteristic
impedance;
Thus, a bridge can be used to determine the presence or
absence of a low SWR.
32
34. To test for a match, the reference impedance of the
bridge is set to the expected load impedance (for
example, 50 Ohms), and the transmission line
connected as the unknown impedance.
RF power is applied to the circuit.
The voltage at the line input represents the vector
sum of the forward wave, and the wave reflected
from the load
If we know the characteristic impedance of the line is
50 Ohms, we know the magnitude and phase of the
forward wave. It's the same wave which is present on
the other side of the detector.
34
35. Subtracting this known wave from the wave at
the line input yields the reflected wave.
Properly designed, a bridge circuit can not
only indicate a match, but the degree of
mismatch – making it possible to calculate the
SWR.
This usually involves alternately connecting
the reference wave and the reflected wave to
a power meter, and comparing the
magnitudes of the resulting deflections.
35
36. 36
Spectrum Analyzer
A Spectrum analyzer measures the magnitude of an input
signal Versus frequency within the full frequency range of
the instrument
It Usually display raw, unprocessed signal information
such as voltage, Power, period Waveshape, sidebands and
frequency.
It can provide a clear and precise window in to the
frequency spectrum
37. 37
Spectrum Analyzer Versus Oscilloscope
Spectrum Analyzer Oscilloscope
Spectrum analyzer gives amplitude v/s
frequency display
An Oscilloscope give amplitude v/s time display of
a wave
It displays frequency components of a wave
and their amplitudes(a spectrum
analyzer shows it with respect to frequency)
It gives distribution of energy in wave with respect
to time(an oscilloscope displays a signal with
respect to time)
To observe the frequency properties of a
signal, a spectrum analyzer is required.
An oscilloscope is used to find the relative time
delay between two signals
A spectrum analyzer can measure and
display signals with analog modulation, such
as amplitude modulation (AM) and frequency
modulation (FM).
An oscilloscopes can only directly measure voltage,
not current. One way to measure AC current with
an oscilloscope is to measure the voltage dropped
across a shunt resistor. ..
The primary use is to measure the power of
the spectrum of known and unknown signals.
The spectrum analyzer is more accurate
The primary function of an oscilloscope is to
measure voltage waves
The Spectrum Analyzer plots the Amplitude
vs. Frequency of the signal.
The oscilloscope plots the Amplitude vs. Time of
the signal,
38. 38
Types of Spectrum Analyzers
Filter Bank Spectrum Analyzer
Superheterodyne spectrum analyzer
Filter Bank Spectrum Analyzer
The spectrum analyzer used for analyzing the signals are of AF range is called filter
bank spectrum analyzer or real time spectrum analyzer because it shows any
variations in all input frequencies, below block diagram shows this,
39. 39
Working of Filter bank spectrum analyzer
It has set of BPF and each one is
designed for allowing a specific
band of frequencies.
The output of each band pass
filter is given to a corresponding
detector
All the detector outputs are
connected to electronic switch
This switch allows the detector
sequentially to the vertical
deflection plate of CRO,SO,
CRO displays the frequency
spectrum of AF signal on its CRT
screen
40. 40
Superheterodyne spectrum analyzer
The spectrum analyzer used for analyzing the signals are of RF range is
called Superheterodyne spectrum analyzer, below block diagram shows
it,
41. 41
Working of Superheterodyne spectrum analyzer
The RF signal ,which is to be analyzed is applied to input attenuator.
If the signal amplitude is too large, then it can be attenuated by an input attenuator
Low pass Filter (LPF) allows only the frequency components that are less than the cut-off
frequency
Mixer gets the inputs from LPF and voltage tuned Oscillator.
It produces an output, which is the difference of frequencies of the two signals that are
applied
The amplified IF signal is applied to detector.
The output of detector is given to vertical deflection plate of CRO, So CRO displays the
frequency spectrum of RF signal on its CRT screen
So it is chosed to a particular spectrum analyzer based on the frequency range of the
signal that is to be analyzed.
42. Network Analyzer
A network analyzer is an instrument that measures the network
parameters of electrical networks.
Network analyzers commonly measure
s–parameters because reflection and transmission of electrical
networks are easy to measure at high frequencies.
Network analyzers are often used to characterize two-port
networks such as amplifiers and filters, but they can be used on
networks with an arbitrary number of ports.
Network analyzers are used mostly at high frequencies, operating
frequencies can range from 1 Hz to 1.5 THz. 42
43. Concept of vector network analyzer
The vector network analyzer utilizes the concept of measuring the
transmitted and reflected waves as a signal passes through a device
under test.
Measuring the transmitted and reflected signals across the band of
interest, and often beyond, enables the characteristics of a device to
be determined.
If both transmitted and reflected signals are used to characterize the
input and also the output then the device can be fully characterized.
This can form a key part of any design or test for an RF circuit. 43
44. ScalarNetworkAnalyzer (SNA)
—measures signal amplitude
properties only, its accuracy is
scalar error correction only
VectorNetworkAnalyzer (VNA)
—measures both signal
amplitude and phase
properties, its accuracy
elaborate vector error
correction
44
Types of Network Analyzer
45. Spectrum Analyzer Versus Network Analyzer
45
Spectrum Analyzer Network Analyzer
Measure signal amplitude characteristics,
carrier level, sidebands, harmonics
Measure response of components, devices
circuits, sub assembles to applied stimulus
Can demodulate and measure complex
signals
Contain sources and receivers
Spectrum analyzers are receivers only(single
channel
Display ratioed amplitude and
phase(frequency, power or time sweeps)
Can be used for scalar component test
(amplitude only) with tracking or external
source
Offers advanced error correction for high
accuracy measurements
46. Difference between RF network analyzers and
spectrum analyzers
Spectrum analyzers
• A spectrum analyzer is intended
for analyzing the nature of
signals that are fed into them.
• spectrum analyzers are normally
used to measure the
characteristics of a signal rather
than a device
• The spectrum analyzer is used to
measure carrier power level,
noise harmonics, etc
RF network analyzers
• A network analyzer, on the other
hand generates a signal and uses
this to analyze a network or
device
• RF Network analyzers are used to
measure components, devices,
circuits, and sub-assemblies.
• The network analyzer is used to
measure the reflection, insertion
loss, S parameters, and
transmission and return loss
46
47. • On the opposite end,
spectrum analyzers
measure the parameters of
a signal and not a device.
• They are commonly
configured without a
source. Spectrum Analyzers
are also more flexible in
terms of their IF bandwidths
to allow a complete range
of signal analysis.
• Network analyzers consist
of multiple receivers plus a
source-receiver that
measures the broadband
frequency by sweeping
power and frequency.
• It seeks a known
signal/frequency of a device
output and, using vector-
correction, gives a more
precise measurement than
the spectrum analyzer.
47
48. Architecture of Network Analyzer
• The basic architecture of a network
analyzer involves a signal generator, a
test set, one or more receivers and
display.
• Most VNAs have two test ports,
permitting measurement of four S-
parameters(s11,s12,s21,s22)but instruments
with more than two ports are available
commercially.
48
49. Vector network analyzer block diagram
49
The diagram shows the very
basic blocks of the VNA
including the signal ports, the
signal separation blocks, the
receiver detector, and finally the
processor and display.
The VNA has precision
connectors on the front panel of
the unit itself and then precision
cables are used to connect these
to the device under test.
Precision cables are required
because the phase and loss of a
standard cable would vary too
much with even slight
movement, etc.
50. To test the device, a variable frequency
signal is generated within the vector
network analyzer and the output is
switched to test the DUT in either one
direction or the other.
In this case the left hand side on the
diagram is selected.
The signal passes to the splitter where one
output is used as the reference signal for
the receiver and the other side is passed to
a direction coupler and then into the DUT
via the external connection on the VNA
and the precision cables.
Power passes through the directional
coupler (directional coupler 1) to the DUT,
but the third port detects the reflected
power and this is connected to the receiver
again.
Power that passes through the device under
test is sampled by directional coupler 2 and
this signal is connected to the receiver.
50
Vector network analyzer block diagram
51. Apart from generating a signal to power the device
under test, the signal source also has an output that
is connected to the receiver.
This enables phase information to be gained from
the detected signals.
The signals are processed by the receiver are then
fed to the processor and display.
This section will again make heavy use of
microprocessor technology to provide the control,
functionality and user friendly displays that are
needed for modern test instrumentation.
51
54. 54
Switch on the klystron power supply and VSWR meter
Adjust the reflector voltage to get some deflection in VSWR meter
Maximize the deflection with AM amplitude and frequency control
knob of power supply
Tune the plunger of klystron mount for maximum deflection
Tune the reflector voltage knob for maximum deflection.
Tune the probe for maximum deflection in VSWR meter
Tune the frequency meter knob to get a dip on the VSWR scale and
note down the frequency directly from the frequency meter
Replace the termination with movable short and detune the
frequency meter
Move probe along with the slotted line, the deflection in VSWR
meter will vary,move the probe to a minimum deflection position, to
get accurate reading; it is necessary to increase the VSWR meter
range dB switch to higher position.
Note and record the position
Procedure
55. 55
Move the probe to next minimum position and record the probe
position again
Calculate the guided wavelength as twice the distance between two
successive minimum positions obtained as above
Measure the waveguide inner broad dimension ‘a’ which will be
around 2.286 cm for X-band waveguide.
Calculate the frequency by following equation
f=
𝑐
𝞴0
=c
1
𝞴2
𝑔
+
1
𝞴2
𝑔
𝞴c =2a
Where C=3X 10
8
-meter/sec is velocity of light in free space
Verify with frequency obtained by frequency meter
Calculation
62. 62
Measurement of Attenuation
Microwave Attenuation
Attenuation is a measure of the reduction in power level experienced by a
signal as it passes through a circuit.
In engineering, attenuation is usually measured in units of decibels per unit length
of medium (dB/cm, dB/km, etc.) and is represented by the attenuation coefficient
of the medium.
In practice, Microwave components and devices often provide some attenuation.
The amount of attenuation offered can be measured in two ways. They are −
Power ratio method and RF substitution method.
Attenuation is the ratio of input power to the output power and is normally
expressed in decibels.
Attenuation in dBs=10 log
𝑃𝑖𝑛
𝑃 𝑂𝑢𝑡
To measure the frequency of a microwave signal, the Resonant
Cavity Frequency Meter is tuned until it resonates at the signal frequency. If a
SWR meter is used as the indicator, resonance will reflect as a decrease (dip) in
the signal level due to the storage of energy in the cavity at resonance.
86. 86
Measurement of Dielectric Constant
Various methods are used to measure the dielectric constant
of a material
Waveguide Method
This method is used to measure the dielectric constant of a lossless or
very low loss solid dielectric material that completely fills a length of
a waveguide.
The end of the sample is terminated in a short circuit. Due to the
termination ,a standing wave is formed inside the waveguide.
Let us assume that the first voltage minimum in the unfilled
waveguide occurs at a distance l0 from the air-dielectric interface
Therefore ,the position of the first voltage minimum in the
unfilled waveguide is at a distance l e + l0.
90. EMI / EMC basics and measurement
methods.
EMI is measured in special rooms called "RF anechoic chambers" There
are strict regulations regarding unwanted electromagnetic emissions, and
all commercially-produced electronic devices must pass emission
certification, to meet FCC and other international standards. This is true for
all developed countries.
The terms Electromagnetic interference (EMI) and electromagnetic
compatibility (EMC) are often used interchangeably when referring to the
regulatory testing of electronic components and consumer goods.
During EMC testing, radiated emissions measurements are made using a
spectrum analyzer and or an EMI receiver and a
suitable measuring antenna. Radiated Emissions (H-field): The magnetic
component of the electromagnetic wave is using a spectrum analyzer and or
an EMI receiver and a suitable measuring antenna.
90
91. Differences between EMC/EMI
EMI stands for electromagnetic interference and is an
electronic emission that interferes with components, RF
systems, and most electronic devices. ... The difference
between EMI and EMC is that EMI is the term for
radiation and EMC merely is the ability for a system to
operate within the presence of radiation.
Causes of EMI
Electromagnetic interference (EMI) is a
disturbance caused by an electromagnetic field which
impedes the proper performance of an electrical
device. EMI can come from man-made or natural
sources such as the sun or the Earth's magnetic fields.
91
92. Design guidelines for EMI and
EMC reduction in a PCB
1.Trace spacing and layout. ...
2.Ground planes. ...
3.Shielding. ...
4.Arrangement of PCB layers: ...
5.Segregate sensitive components. ...
6.Decoupling capacitor. ...
7.Controlled impedance for transmission line
design
92
93. What is EMC
Electromagnetic Compatibility Basics
EMC is of increasing importance as the number of wirelessly connected
devices increase. Defining what EMC is and understanding the concepts
enable electromagnetic compatibility to be achieved from the outset.
Electromagnetic compatibility, EMC is the concept of enabling different
electronics devices to operate without mutual interference -
Electromagnetic Interference, EMI - when they are operated in close
proximity to each other.
All electronics circuits have the possibility of radiating of picking up
unwanted electrical interference which can compromise the operation of
one or other of the circuits.
EMC definition: EMC is defined as the ability of devices and systems to
operate in their electromagnetic environment without impairing their
functions and without faults and vice versa.
Electromagnetic compatibility, EMC ensures that operation does not
influence the electromagnetic environment to the extent that the functions
of other devices and systems are adversely affected.
93
94. EMC basics
The aim of employing EMC measures is to ensure that a variety of
different items of electronics equipment can operate in close
proximity without causing any undue interference.
The interference that gives rise to impaired performance is known as
Electromagnetic Interference, EMI. It is this interference that needs
to be reduced to ensure that various items of electrical equipment
are compatible and can operate in the presence of each other.
There are two main elements to EMC:
Emissions: The EMI emissions refer to the generation of unwanted
electromagnetic energy. These need to be reduced below certain
acceptable limits to ensure they do not cause any disruption to other
equipment.
Susceptibility & immunity: The susceptibility of an item of
electronics to EMI is the way it reacts to unwanted electromagnetic
energy. The aim of the design of the circuit is to ensure a sufficiently
high level of immunity to these unwanted signals.
94
95. EMC standards
With the growing awareness and need to maintain high standards of
electromagnetic compatibility many standards have been introduced to help
manufacturers meet the levels they need to maintain full electromagnetic
compatibility.
Many years ago the levels of EMC were low and interference often occurred -
taxis driving past a house whilst using their radio telephone were quite likely
to disrupt the operation of a television, and there were many other instances.
As a result, it became necessary to introduce EMC standards to ensure the
required levels of compatibility were attained.
EMC is now an integral part of any electronics design project. With standards
now implemented and enforced across the world, any new product needs to
meet and have been tested to ensure it meets the relevant EMC standards.
While this presents an additional challenge to the electronics design engineer,
it is essential that good EMC practices have been employed and that the EMC
performance of the product is sufficient to ensure it operates correctly under
all reasonable scenarios.
95
96. EMI Electromagnetic Interference: the
fundamentals
Electromagnetic Interference, EMI is the interference caused by
one electrical or electronic device to another by the
electromagnetic fields set up by its operation.
Electromagnetic interference, EMI
• Electromagnetic interference, EMI is the name given to the
unwanted electromagnetic radiation that causes potential
interference to other items of electronics equipment.
• There are many ways in which electromagnetic interference can
be carried from one item of equipment to another. Understanding
these methods is a key to mitigating the effects of the
electromagnetic interference
96
97. EMI can be divided into two categories:
Continuous interference: The continuous interference
is often in the form of a radio signal or oscillation that is
maintained. It could be from an unscreened oscillator, or
it may be in the form of wideband noise.
Impulse interference: This form of interference
consists of a short impulse. It may arise from an
electrostatic discharge, lightning, or a circuit being
switched.
• Apart from understanding the form of the interference, it
is also necessary to know how the interference is
travelling from the transmitting device to the receiving
device. Unfortunately this is not always easy to discover
as many of the paths are difficult to define. However good
initial design alleviates many problems.
97
98. • There are many forms of electromagnetic interference, EMI that can
affect circuits and prevent them from working in the way that was
intended. This EMI or radio frequency interference, RFI as it is
sometimes called can arise in a number of ways, although in an ideal
world it should not be present.
• EMI - electromagnetic interference can arise from many sources, being
either man made or natural. It can also have a variety of characteristics
dependent upon its source and the nature of the mechanism giving rise
to the interference.
• By the very name of interference given to it, EMI is an unwanted signal
at the signal receiver, and in general methods are sought to reduce the
level of the interference.
• Types of EMI - Electromagnetic Interference
• EMI - Electromagnetic Interference can arise in many ways and from a
number of sources. The different types of EMI can be categorised in a
number of ways.
• One way of categorising the type of EMI is by the way it was created:
• Man-made EMI: This type of EMI generally arises from other
electronics circuits, although some EMI can arise from switching of
large currents, etc.
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99. Naturally occurring EMI: This type of EMI can arise from many sources - cosmic
noise as well as lightning and other atmospheric types of noise all contribute.
Another method of categorizing the type of EMI is by its duration:
Continuous interference: This type of EMI generally arises from a source such as a
circuit that is emitting a continuous signal. However background noise, which is
continuous may be created in a number of ways, either manmade or naturally occurring.
Impulse noise: Again, this type of EMI may be man-made or naturally occurring.
Lightning, ESD, and switching systems all contribute to impulse noise which is a form
of EMI.
It is also possible to categories the different types of EMI by their bandwidth.
Narrowband: Typically this form of EMI is likely to be a single carrier source -
possibly generated by an oscillator of some form. Another form of narrowband EMI is
the spurious signals caused by intermodulation and other forms of distortion in a
transmitter such as a mobile phone of Wi-Fi router. These spurious signals will appear at
different points in the spectrum and may cause interference to another user of the radio
spectrum. As such these spurious signals must be kept within tight limits.
Broadband: There are many forms of broadband noise which can be experienced. It
can arise from a great variety of sources. Man-made broadband interference can arise
from sources such as arc welders where a spark is continuously generated.
Naturally occurring broadband noise can be experienced from the Sun - it can cause sun-
outs for satellite television systems when the Sun appears behind the satellite and noise
can mask the wanted satellite signal. Fortunately these episodes only last for a few
minutes.
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106. The FCC and NTIA Licensing Process
The FCC ruling also permits a simplified licensing scheme for millimeter-wave radios, allowing
cheap and fast allocations to prospective users: You can apply for a 10-year license, get
accepted, and pay for it in less than 30 minutes for only a few hundred dollars.
The FCC will issue an unlimited number of non-exclusive nationwide licenses to non-federal
government entities in the 12.9 GHz of spectrum allocated for commercial use. These licenses
will serve as a prerequisite for registering individual point-to-point links.
The 71-95 GHz bands are allocated on a shared basis with federal government users. Therefore,
in order to operate a link under its non-exclusive nationwide license, licensee will have to:
Coordinate with the National Telecommunications and Information Administration
(NTIA) with respect to federal government operations. Register as an approved link
with a third party Database Manager.
On September 29, 2004, the Wireless Telecommunications Bureau (WTB) appointed
Comsearch, Frequency Finder, and Micronet Communications as independent Database
Managers responsible for the design and management of the third-party 71- 95 GHz bands Link
Registration System (LRS). Proposed links must be coordinated with NTIA.
NTIA has developed an automated coordination mechanism that can determine whether a
given non-federal government link has any potential conflict with federal government users. A
proposed link entered into NTIA’s automated system will result in either a “green light” or a
“yellow light” based on the proposed parameters.
Licensing MMW radios is simple and inexpensive: A 10- year license costs a few hundred dollars
and only takes about a half-hour to apply for.
107. Despite some issues and technical challenges,
MMW radios are promising candidates for multigigabit rates in
point to-multipoint and point-to-point applications.
The huge unlicensed bandwidth, coupled with higher allowable
transmission power and advances in integrated circuit
technology, have made millimeter wave radios promising
candidates for multi-gigabit rates in point-to-multipoint and
point-to-point applications.
A number of open issues and technical challenges have yet to be
fully addressed.
In particular, propagation and implementation issues require
further optimization and research in order to obtain a truly
efficient and low-cost millimeter wave communication system
Multi GBPS data communication and system requirements
108. Research & Development
• https://www.drdo.gov.in/labs-and-
establishments/microwave-tube-research-
development-centre-mtrdc
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