Transcript Wavelength

RF & Microwave
Fundamentals
Jan 2006
Anritsu Korea
Slide 1
0
Basic Fudamentals
• Definition of Terms
• What Does RF Mean?
• Basic Concepts
• Transmission Lines
• Coaxial Cable
• Waveguide
• Transmission Line Theory
• Transmission measurements
• Return Loss measurements and
error analysis
• Advanced Measurement
Techniques (air lines)
• S Parameters & VNA measurement
fundamentals
• Common Microwave Devices and
measurements
• Synthesizer related RF Concepts
and error analysis
Slide 2
0
Electromagnetic Spectrum



RF Radio Frequency. A general term used to
describe the frequency range from 3 kHz to 3.0
GHz (Gigahertz )
Microwave. The frequency range 3GHz to 30.0
GHz. Above 1 GHz, lumped circuit elements are
replaced by distributed circuit elements.
Millimeter wave. The frequency range 30 GHz to
300 GHz. The corresponding wavelength is less
than a centimeter.
Slide 3
0
Range of RF Frequencies
Medium Frequency (300 KHz - 3 MHz)
 High Frequency (HF) (3 - 30 MHz)
 Very High Frequency (VHF)
(30 - 300 MHz)
 Ultra High Frequency (UHF)
(300 - 3000 MHz)

Slide 4
0
Some Terms You Will Hear
dB
 dBm
 Impedance
 Return Loss (RL)
 Insertion Loss (Cable Loss)
 VSWR
 DTF
 Watts

Slide 5
0
Linear vs Log
Some things are very, very large.
 Some things are very, very small.

It is difficult to express comparison of sizes
in common units of measure with a linear
scale.
One would not usually express a flea’s dimensions in
miles, for example.
Slide 6
0
Bel

A bel is defined as the logarithm of a
power ratio.
Po
bel = log
Pi
Slide 7
0
Decibel (dB)

Decibel (dB) is a logarithmic unit of
relative power measurement that expresses
the ratio of two power levels.
Po
dB = 10 log
Pi
Slide 8
0
dBm

dBm is the decibel value of a signal
compared to 1 m w.
Slide 9
0
3 dB rule
+3 dB means double the power (multiply
by 2)
 - 3 dB means halve the power
(divide by 2)

Slide 10
0
Power Conversion Table

Some common decibel values and powerratio equivalents.
Slide 11
0
Basic Concept
Wavelength ()
Length
Slide 12
0
Wavelength ()
VC
() =
εr f
Where: VC = velocity of propagation through
air
εr = relative dielectric constant
f = frequency of oscillation
Slide 13
0
Velocity of Propagation

Electromagnetic energy travels at the speed
of light.
Slide 14
0
Time Domain and Frequency Domain
Slide 15
0
Transmission Line Theory
Must be applied when line lengths are > ( / 4 )
 Standard lumped-circuit analysis can be applied
when the line lengths are << ( / 4 )

Slide 16
0
Impedance
 The
impedance of a transmission line
can be complex
Z = R ± jX
If X is positive, it is called the inductive
reactance
If X is negative, it is called capacitive
reactance
Impedance plot in a rectangular coordinate
Slide 17
0
Different Types Transmission
Line
 There are many different types of
transmission lines and we will talk about
three of them.
 Coaxial
 Waveguide
 Microstrip
Slide 18
0
Coaxial Cable
Slide 19
0
Waveguide

Waveguide is a hollow, conducting tube,
through which microwave frequency
energy can be propagated.
Slide 20
0
Microstrip Transmission Line
Microstrip line
W
Ground Plane
h
Dielectric
Slide 21
0
Characteristic Impedance of
Coax
For a lossless line R=G=0
Zo
Z
L
Y
C
Slide 22
0
Characteristic Impedance
¥
I = (E/Z0)
ZL = Z0
¥
Z0
Z0 = (138/
εR) Log (D/d)
Slide 23
0
Propagation Modes of Coax

Patterns set up by electric and
magnetic fields.
Slide 24
0
Cutoff Frequency

The lowest frequency at which the next
higher order mode can propagate is
called the cut-off frequency of the next
higher order mode.
Slide 25
0
Velocity of Propagation
In free space C = 3x108 m/sec
Wavelength = λ = C/f
Where f = frequency (Hz)
Slide 26
0
Relative Velocity Constant (k)
k = (1/ εR)
for Teflon: εR = 2.04
k = (1/
2.04) = 0.7
Slide 27
0
Phase of The Signal at One
Wavelength
The phase of the signal at one wavelength intervals
along the line will be in phase. In this instance λ0
is 21 cm at 1 GHz.
Slide 28
0
Well Matched Transmission Line
If Z0 = ZL
then P0 = PL
No reflection
PI
Z0
P0
ZL
Therefore PL = PI
Slide 29
0
PL
Poorly Matched Transmission Line
If ZL ≠ Z0
then PL ≠ PI
Reflection is
present
PI
Z0
PR
P0
ZL
Therefore PL = PI - PR
Slide 30
0
PL
Example
Short at the end of the line
Slide 31
0
SWR Vs Impedance
ZL  0, ZL  ¥ and ZL  Z0
Slide 32
0
VSWR
Voltage Standing Wave Ratio (VSWR)
Emax
ER + EI
 VSWR =
=
Emin
ER - EI

ER

G(reflection coefficient) =
EI
Slide 33
0
Reflection Terms &
Relationships
Slide 34
0
Reflection
Slide 35
0
Reflection Coefficient
Reflection coefficient is the ratio of the
reflected signal to the incident signal.
ZL - Z0
ER/Ei = G = |G|  =
ZL + Z0

Slide 36
0
Mismatch
Mismatch is a measure of the efficiency of
power transfer to the load. The percentage
of the power reflected from the Load.
0 dB return loss or infinite VSWR indicate
perfect reflection by the load.
Infinite return loss or unity VSWR indicate
perfect transmission to the load.
Slide 37
0
Basic Measurements
Transmission Loss/Gain = Pout/Pin
Return Loss = Preflected/Pin
Slide 38
0
Transmission Measurement

Combining Signals
Slide 39
0
Calculating dB Difference
Slide 40
0
Power Gain

Gain is the ratio of the
output power level of
an amplifier to the
input power level to
that amplifier.
Po
Gain =
Pi
Slide 41
0
Transmission Measurement
(Loss/Gain Measurement)
VI
Source

Log Amp Display
VO
DUT
Detector
Transmission Power Gain = 20 log (Vo/Vi)
Slide 42
0
Making a Transmission
Measurement
Measure incident power going into the
device.
 Measure the output power coming out of
the device.
 The difference in power is transmission
loss (or gain).

Slide 43
0
Measure Incident Power

Using detector directly on the test port.
Source
Detector
Slide 44
0
Measure Output Power
SOURCE
DUT
DETECTOR
Slide 45
0
Transmission Measurement Errors
•
•
•
•
Calibration Error
Test Port Match
Detector Match
Using Adapters
Slide 46
0
Calibration Error
Slide 47
0
Determining Calibration Error
Slide 48
0
Test Port Match Error
Slide 49
0
Detector Match Error
Slide 50
0
Calculating the Errors
Slide 51
0
Error Calculation
Slide 52
0
Error Example
Transmission Measurement Errors
Output Match
Port Match
20 dB
15 dB
Source
Port Match
15 dB
Insertion
Loss
1 dB
Input Match
20 dB
Detector
A)
3( Insertion Loss) + Detector + Source
B)
Insertion Loss + Detector + DUT Output
C)
DUT Input + Source + Insertion Loss
Slide 53
0
Error Calculation
Slide 54
0
Maximum Effect
Slide 55
0
RSS
Slide 56
0
Total Error
Slide 57
0
What happens when you add an adapter?
Slide 58
0
Example 1
Slide 59
0
Example 2
Slide 60
0
Improving Transmission Loss
Measurements
Use detectors with better match.
 Use attenuator pads or isolators between
test port and DUT and detector and DUT to
diminish magnitude of the error signals.

Slide 61
0
Return Loss
 Return
Loss Measurements
 Uncertainty analysis
Slide 62
0
Return Loss Measurements
Problem: How do you separate reflected
signal from incident signal
Slide 63
0
Solution to R L Measurements

Solution:
Directional Devices

Definition:
A directional device is able
to separate either the incident or the
reflected signal from the environment
where both exist.
Slide 64
0
Solution to RL Measurements
Directional Devices:
Couplers (Coaxial and
Waveguide), Bridges,
Autotesters
Incident
power
Reflected
power
Port 1
Port 2
Dual Directional Coupler
Slide 65
0
Making a Return Loss
Measurement
Two requirements when measuring return
loss
 Separation of incident and reflected signal

Establish a 100% reflection reference
Slide 66
0
100% Reflection Reference
For COAX two references exist:
Open circuit
Short circuit
They are 180° out of phase
For Waveguide two reference can be used
short circuit and offset short
Slide 67
0
100% Reflection Reference
The Average of an Open & Short represents
a “true” 100% reflection.
Slide 68
0
Return Loss Block Diagram
Slide 69
0
Errors to Consider
• Directivity
• Test port match
• Termination error
Slide 70
0
Calculating Directivity
Source
VIN
Directional
Device
Perfect
Termination
VOUT
Directivity = 20 log ( Vin/ Vout) dB
Example: Vin = 1 Volt, and Vout = 10mV
Directivity = 20 log ( 1/ .01) = 40 dB
Slide 71
0
Test Port Match
Slide 72
0
Termination Error
Errors in Return Loss
Termination Error: The additional reflection
that an imperfect termination causes.
Slide 73
0
Termination Error
Slide 74
0
Calculating the Errors
Directivity Error
+ Test Port Match Error
+ Termination Error
?
Do it exactly the same way as you did
transmission loss.
Slide 75
0
Calculating the Errors




Calculate how far below the desired signal the
error signal is (in dB).
Convert the dB into linear (reflection
coefficient) form. Use reflection chart or
calculate.
GE = log-1 [ -dB error/20]
For worst case, add up all linear terms.
Sum = GE1 + GE2 + GE3
Slide 76
0
Calculating the Errors

Effect on the measurement is the linear
sum adding in phase or subtracting out of
phase from the nominal return loss of the
device under test.
Measurement = GDUT ± GSUM
In dB, meas. Max = - 20 log [GDUT - GSUM]
Min = - 20 log [GDUT + GSUM]
Slide 77
0
Error Signal Return Loss
(Reflection)
Slide 78
0
Calculating the Errors
Autotester
Directivity = 40 dB (.01 G)
dB(.178 G)
Test Port = 20 dB (.1 G)
Termination
Return Loss = 40 dB (.01G)
DUT
Input/Output Match = 15
Insertion Loss = 1 dB
Detector
Return Loss = 20 dB (.1G)
Slide 79
0
Return Loss Measurement Errors
With Termination
Errors:
A) 2(I.L.) + Termination
2 dB + 40 dB = 42 dB
B) 2 (DUT) + Test Port
(.008G)
30 dB + 20 dB = 50 dB (.0032G)
C) Directivity
= 40 dB (.01G)
Total Error = 0.021G
Slide 80
0
Measured Results For Using
Termination
DUT = .178G
(15 dB) (1.43 SWR)
Plus Total Error + .021G
.199G = (14.02 dB) ( 1.50 SWR)
DUT = .178G
(15 dB) (1.43 SWR)
Minus Total Error - .021G
.157G = (16.08 dB) (1.37 SWR)
Slide 81
0
Measured Results For Using
Detector
With Detector (as termination)
A)
B)
C)
2 (I.L.) + Detector
2 dB + 20 dB = 22 dB
2(DUT) + Test Port = 50 dB
Directivity = 40 dB
(.079G)
(.0032G)
(.01G)
.092G
Measured Results
DUT + Total Error
.178G + .092G = .270G
DUT - Total Error
.178G - .092G = .086G
(11.37 dB) (1.74 SWR)
(21.31 dB) (1.19 SWR)
Slide 82
0
Error Signals
Adapter
DUT
Directivity = 40 dB
Test Port Match = 20 dB
Adapter = 36 dB
DUT = 15 dB
A- Effective Directivity
Directivity = 40 dB (.01G)
Adapter = 36 dB (.0158G)
Minimum Effective Directivity
Autotester = 40 dB = .01G
Plus Adapter Error + .0158G
.0258 = 31.77 dB
B- Effective Test Port Match
Autotester = 20dB = (.1G)
Adapter = 36 dB = (.0158)
Minimum Effective Test port Match
Autotester = 20dB = .1G
Plus Adapter error + .0158G
.1158G = 18.73 dB
Slide 83
0
Input Match Errors Due to Sweeper Output and SWR
Autotester Input Match
Effective Input Match
dB
Sweeper Input Match 16 =
Autotester Input Match 20 =
G
.159
.10
Effective Input Match = 11.7 dB .259
11.7 dB Effective Input
IL = 6.5 dB
Slide 84
0
Input Match Error Signal
Error = DUT + IL + Input + IL + DUT
15 dB + 6.5 dB + 11.7 dB + 15 dB
dB
54.7
Error Analysis
=
40
.00185
G
dB
Directivity
Test Port
2(DUT) + Test Port
Input
G
=
=
50 =
=
54.7 =
Total Error
.01
.0032
.00185
.01505
DUT = 15 dB = .178
Plus Error
+ .01505
.1931 = 14.28 dB
DUT = 15 dB = .178
Minus Error - .01505
.1630 = 15.78 dB
Slide 85
0
Example 3
Slide 86
0
Example 4
Slide 87
0
Have We Forgotten Something?

Instrumental Errors

Connector Repeatability
Slide 88
0
Instrumental Errors




Signal source harmonics
Network Analyzer/Detector deviation from
logarithmic response (.01 dB per dB of
measurement)
Readout Error (manual .03 to .1 dB, automated
.01 dB)
Signal source power and frequency stability
Slide 89
0
Connector Repeatability
APC-7
N
SMA
K
V
Typically
Typically
Typically
Typically
Typically
±
±
±
±
±
0.02 dB
0.03 dB
0.04 dB
0.035 dB
0.045 dB
Slide 90
0
Summary
Insertion Loss
Errors normally 10 % or
higher, limited by device
matches and instrumental
errors.
Medium Loss Errors normally less than 10 %
Low Loss
(0 to 8 dB)
(6 to 20 dB)
Higher Loss
(20 dB)
Errors normally less than 2 %.
Dynamic range of detectors
becomes limiting factor for
very high attenuation values.
(> - 40 dBm output level)
Return Loss
Errors normally 10 % or higher,
limited by test port match and
instrumental errors.
Errors normally less than 10 %
for directional devices with
greater than 35 dB directivity.
Errors normally greater than
10 % limited by directivity of
directional devices.
Slide 91
0
S Parameters & VNA
Measurement Fundamentals
Slide 92
0
S Parameters
S21 FORWARD TRANSMISSION
Port 1
Port 2
a1
S11 FORWARD
REFLECTION
b2
DUT
S22 REVERSE
REFLECTION
b1
a2
S12 REVERSE TRANSMISSION
Slide 93
0
S Parameters
b1
S11  a1  S12  a2
b2
S21  a1  S22  a2
 b1 
 
 b2 
 S11 S12   a1 

  
 S21 S22   a2 
Slide 94
0
S Parameters Defined
•
•
•
•
•
S11= Forward Reflection (b1/a1)
S21= Forward Transmission (b2/a1)
S22= Reverse Reflection (b2/a2 )
S12= Reverse Transmission (b1/a2)
All are Ratios of two signals - (Magnitude
and Phase)
Slide 95
0
Diagram for S-Parameters
a1
b2
S21
S11
S22
a2
b1
S12
T1
T2
Slide 96
0
Impedance Components
The relationship between the reflection coefficient
and the impedance on a transmission line
G ( z)
z( z)
Z( z)  Zo
Z( z)  Zo
Z( z)  1  G ( z) 

Zo  1  G ( z) 
Slide 97
0
Smith Chart
Slide 98
0
Impedance Components
The impedance components in the Smith
chart are:
 The resistive components
 The reactive components
A- Inductive
B- Capacitive
Slide 99
0
Constant Resistance Circles
Slide 100
0
Inductive Reactance Circles
Slide 101
0
Capacitive Reactance Circles
Slide 102
0
Using Smith Chart
Slide 103
0
What’s the difference between a VNA and a Scalar
Analyzer?
• A Vector Network Analyzer not only measures
the magnitude of the reflection or transmission,
but it also measures its PHASE.
• A Scalar Network Analyzer uses a diode to
convert energy to a DC voltage. It can only
measure magnitude with limited dynamic range.
• A Vector Analyzer uses a tuned receiver followed
by a quadrature detector, so phase can be
measured. Ratio measurements and the benefits
of the heterodyne process all contribute to overall accuracy and dynamic range.
Slide 104
0
What is phase?
t
These two signals have the
same magnitude but are 90
degrees out of phase!
Slide 105
0
Phase
• Using phase information, one can
calculate the electrical delay through a
device.
• Analyzing the variation of phase shift
through a device with respect to
frequency, one can calculate group delay.
• Group delay is one cause of distortion in
voice transmission and bit errors in digital
transmission systems.
Slide 106
0
What happens when two equal signals
which differ by 180 degrees are summed?



The resultant depends on their relative amplitudes
If the amplitudes are equal - They completely
cancel -

This is not hypothetical - When a full reflection
occurs at the end of a transmission line, all of the
incident energy is reflected back to the generator

This causes high standing waves

Depending where you “look” along the line,
you could see ZERO or Twice the loaded Voltage !!



Slide 107
0
How does a VNA
display the S-parameters?
Log Magnitude
and Phase
Slide 108
0
Another VNA Display Mode
Smith Chart
Slide 109
0
VNAs and Calibration
Slide 110
0
VNA Test Set and Source
Source
Transfer Switch
Power
divider
Rear Panel
Reference
Loops*
a2
a1
4 Samplers
Coupler
40dB Step
Attenuator**
b2
b1
Port 1
Port 2
DUT
Slide 111
0
Without calibration a VNA cannot make
accurate measurements

Calibration means removing errors

Types of errors to deal with:
• Random Errors (i.e. Connector Repeatability)
– Cannot be calibrated out, due to randomness.
• Systematic Errors
– CAN be reduced via calibration
– Transmission and Reflection Frequency Response Errors
– Source and Load Match Errors
– Directivity and Isolation (Crosstalk) Errors
Slide 112
0
Error Vectors



Once the error
vector is known
(Mag. & Phase)
It can be vectorially
added to the raw
VNA measurement
Resultant is the
actual DUT
performance!
x
Slide 113
0
Error Vectors
Coupler
DUT
RCVR
Exf
1
Edf
Etf
Esf
Erf
S11
S22
Elf
S12
Forward Direction
Slide 114
0
Error Vectors
S21
Elr
Etr
S11
S12
Err
S22
Esr
Edr
1
Exr
Reverse Direction
Slide 115
0
How to CalibrateTo reduce the systematic errors for both
ports (Forward and Reverse), a 12 term
calibration is required.
 Open Short Load Through (OSLT)

• The most common coax calibration method

Other calibration techniques
• LRL, LRM, TRM, Offset Short...

Exercise Good Techniques for best results
• Practice/Care/Knowledge/Clean Parts
Slide 116
0
How does calibration work?

The VNA measures KNOWN standards.

It will compare the measured value to the
known value, and calculate the difference.

The difference is the error. It will store an
error coefficient (Magnitude and Phase) at
every frequency/data point, and use it when
making measurements.
Slide 117
0
ALL MEASUREMENT ARE REFERENCED
TO A STARTING POINT
PHASE MEASUREMENTS BEGIN BY UNDERSTANDING
WHERE THE REFERENCE PLANE IS
POINT IS THE REFERENCE PLANE
Slide 118
0
WHY MUST WE MEASURE
PHASE???
• ERROR CORRECTION REQUIRES THAT WE
HAVE PHASE AND MAGNITUDE
INFORMATION – EVEN IF WE ARE ONLY
CONCERNED WITH MAGNITUDE DURING
TESTING!
• All four S Parameters are interdependent, so
we must constantly reverse to compensate
for Source Match, Load Match, Directivity,
Frequency Response (Reflection),
Frequency Response Transmission, and
Isolation.
Slide 119
0
Systematic Error
Transmission Frequency Response
 Reflection Frequency Response
 Source Match
 Load Match
 Directivity
 Isolation (Crosstalk)
Reduced by Calibration
 These Six Terms on both Ports, yield 12
Term Error Corrected Data.

Slide 120
0
Corrected S-parameters
Slide 121
0
Calibration - (Open, Short
Load, Thru)
The most common calibration type is the OSL.

Open
• Infinite Impedance
• Voltage Maximum
• O degree Phase Reflection
• Reflection Magnitude = 1

Short
• Zero Ohms Impedance
• Voltage Null
• 180 degrees Phase Reflection
• Reflection magnitude = 1

Load (Broadband)

Through
• Test ports connected together
for transmission calibration
measurement
•
50 Ohms (match)
•
Reflection Magnitude = 0
Slide 122
0
Calibration – OSL Sliding Load
Due to the difficulty of producing a high
quality coaxial termination (load) at
microwave frequencies, a sliding load can be
used at each test frequency to separate the
reflection of a somewhat imperfect
termination from the actual directivity
 Broadband measurements required high
accuracy must use 12 Term sliding load
calibration

Slide 123
0
VNA Measurement Uncertainties
The quality of a VNA measurement can be
affected by the following :
 The Quality of the Calibration Standards
 Error Correction Type used – 12 Term, 1
Path 2 Port, and etc.
 Dynamic Range of the measurement system
(VNA) – IFBW, Averaging and etc.
 Cable stability and Connector repeatability
Slide 124
0
Uncertainty Curve
Slide 125
0
Exact Uncertainty
A
Windows based program is available
to help obtain the uncertainty data that
is appropriate for the customer’s
specific application.
 CDROM part number 2300-361
 Application Note 11410-00270
Slide 126
0
Measurement Uncertainty
Exercise
Slide 127
0
Common Microwave
Devices
Slide 128
0
What do our Customers manufacture?





Amplifiers
Mixers
Power Dividers
Power Splitters
Combiners





Couplers
Circulators
Isolators
Attenuators
Filters
Slide 129
0
Amplifier


An Amplifier is an active RF component used to increase the
power of an RF signal.
Four fundamental properties of amplifiers are:
•
•
•
•
Input/Output Matches
Gain
Noise figure
Linearity - 1 dB Compression point
Small signal in

Big signal out
Slide 130
0
Match and Gain
 Use
the Transmission/Reflection
Measurement mode of the VNA to
measure these parameters:
• Input match – S11
• Output match – S22
• Gain – S21
Slide 131
0
Noise
 We
are interested in specific manmade signal
 But there are some unwanted signals
combined with our desired signal.
 Thermal Noise
Slide 132
0
Noise Measurement
 There
are many ways to express noise.
 Noise may be expressed in Noise
Factor which is defined as the input
signal-to-noise ratio to the output
signal-to-noise ratio.
Si/Ni
F=
So/No
Slide 133
0
Noise Figure
 Noise
can be expressed in Noise
Figure which is the logarithmic
equivalent of Noise Factor.
Si/Ni
NF = 10 log
So/No
Slide 134
0
Noise Figure Measurement
Slide 135
0
Linearity
 Linearity
is a measure of how the gain
variations of an amplifier as a function
of input power distorts the fidelity of the
signal.
Output power VS Input power of an amplifier
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1-dB Compression Point
Input signal (dBm)
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Gain Compression
 Traditionally,
power meter is used for
this measurement – tedious procedure
 VNA can now be used – very quick and
simple
 Two VNA approaches are available:
• Swept Frequency Gain Compression
• Swept Power Gain Compression
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Swept Frequency Gain
Compression
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Swept Power Gain
Compression
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Third-order Intercept Point
(TOIP)
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TOIP
Third-order intercept point (TOIP)
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Intermodulation Products
 Understanding
the dynamic
performance of the receiver requires
knowledge of intermodulation products
(IP).
 How intermodulation is created?
 What are the intermodulation
products?
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Intermodulation
(Continued)
Frequencies causing problem
 Overdriven amplifier or receiver

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IMD/TOI Measurement Setup
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IMD Measurements
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TOI Measurement
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Mixer
A
Mixer is a three-port component
used to change the frequency of one of
the input signals.
 Fundamental properties of mixers are:
•
•
•
•
Conversion gain/loss
Port Match
Isolation
Intermodulation Distortion (IMD)
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Conversion Gain/Loss, Isolation
& Port Matches
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Mixer IMD Measurement
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Power Divider
A
Power Divider (also called three-resistor power splitter)
is a bi-directional device that equally
divides an RF signal with a good match
on all arms.
Input
Output 1
Output 2
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Power Splitter

A Power Splitter (also called two-resistor power splitter)
is a passive RF device that equally
divides an RF signal into two RF signals.
Output 1
Input
Output 2
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Combiner
A
Combiner is a passive RF device
used to add together, in equal
proportion, two or more RF signals.
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Coupler


Directional coupler
Bidirectional coupler
A
C
B
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RF Hybrid Coupler
 The
RF hybrid coupler is a device that
will either
(a) split a signal source into two directions or
(b) combine two signal sources into a common path.
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Applications of hybrids
Combining two signal sources
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Circulator and Isolator
A circulator is a passive junction of three or
more ports in which the ports can be
accessed in such an order that when power
is fed into any port it is transferred to the
next port, the first port being counted as
following the last in order.
 An isolator is a 3-port circulator with the third
port terminated with a load so that power
can only be transferred in one direction from
the first port to the second port.

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Multi-port Devices
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Attenuator
 An
Attenuator is a RF component used
to make RF signals smaller by a
predetermined amount, which is
measured in decibels.
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Dynamic Range
Dynamic Range is basically the difference
between the maximum and minimum signals
that the receiver can accommodate. It is
usually expressed in decibels (dB).
 It is essential that the measurement
instrument has sufficient dynamic range to
accurately characterize an attenuator.

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Attenuator Measurements
Slide 161
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Attenuator Measurements
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Filter

A Filter transmits only part of the incident energy
and may thereby change the spectral distribution of
energy:
•
•
•
•
High pass filters transmit energy above a certain frequency
Low pass filters transmit energy below a certain frequency
Band pass filters transmit energy of a certain bandwidth
Band stop filters transmit energy outside a specific
frequency band
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Filter Measurements
Slide 164
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