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8/6/2019 S-Parameters Self Reading 2
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Bhaskar Banerjee, EE7V82 Spring 2010 1
Transmission Lines and S-Parameters
Prof. Bhaskar Banerjee
EE 7V82 - RF IC Design
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Bhaskar Banerjee, EE7V82 Spring 2010 2
Transmission Lines
Transmission line theory is basic for any high frequency design
Microstrip
h
w
Coplanar
w1
w2
WaveguideTwisted-pair Coaxial
b
ah
w
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Bhaskar Banerjee, EE7V82 Spring 2010 3
Basic Concepts on Transmission Lines
A portion of the power generated by a source (Gen.) is delivered to aload (Z L) by means of a transmission line (TL) Voltage , current , and power can be considered to be in the form
of waves traveling in both directions along the transmission line Incident and reected voltages on a TL results in a standing
voltage wave on the line
TL(Zo)
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Bhaskar Banerjee, EE7V82 Spring 2010 4
Termination of Transmission Lines
Waves on TL with different termination impedances
For reection, a transmission line terminated in Zo behaveslike an innitely long transmission line
For reection, a transmission line terminated in a shortor open reects all power back to source
Standing wave pattern does not go to zero aswith short or open
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Bhaskar Banerjee, EE7V82 Spring 2010 5
Power Transfer on Transmission Line Low frequencies : wavelength >> wire length
Current (I) travels down wires easily for efcient power transmission Measured voltage and current not dependent on position along wire
High frequencies : wavelength
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Bhaskar Banerjee, EE7V82 Spring 2010 6
Power Transfer on Transmission Line Maximum power transfer
It should be considered in a transmitter of RF system
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Bhaskar Banerjee, EE7V82 Spring 2010 7
Power Transfer on Transmission Line
Maximum power transfer
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Bhaskar Banerjee, EE7V82 Spring 2010 8
50 Transmission Lines
Why 50 ?
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Bhaskar Banerjee, EE7V82 Spring 2010 9
Network Characterization Two-port network parameters
Open-circuit parameters (Z-parameters) Short-circuit parameters (Y-parameters) Hybrid parameters (H-parameters) Transmission parameters (ABCD-parameters)
Features Based on voltage (V) and current (I) Requires open and short terminations
Z11 =V1I1 I2=0
Z21 =V2I1 I2=0
Z12 =V1I2 I1=0
Z22 =V2I2 I1=0
H11 =V1I1 V2=0
H12 =I2I1 V2=0
H12 =V1V2 I1=0
H22 =I2V2 I1=0
Y11 =I1V1 V2=0 Y21 =
I2
V1 V2=0Y12 =I1V2 V1=0 Y22 =
I2V2 V1=0
A =V1V2 I2=0
B =V1
- I2 V2=0C =
I1V2 I2=0
D =I1
- I2 I1=0
Open termination
Short termination
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Bhaskar Banerjee, EE7V82 Spring 2010 10
Why S-Parameters?
Problems on traditional network parameters when moving tohigher frequencies Equipment is not readily available to measure total voltage
and total current at the ports of the network Short and open circuit are difcult to achieve over a broad
band of frequencies
Active devices, such as transistors and tunnel diodes, very often will not be short and open circuit stable
Therefore, some method of characterization is necessary toovercome these problems Scattering parameters (S-parameters)
The logical variables to use at high frequencies are traveling waves rather than total voltages and currents
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Bhaskar Banerjee, EE7V82 Spring 2010 11
Two-port S-parameters Derivation
Generalized scattering parameters have been dened by K. Kurokawa Refer K. Kurokawa, Power waves and the scattering matrix, IEEE Trans.
MTT, Vol. 13, No. 2. Mar. 1965
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Bhaskar Banerjee, EE7V82 Spring 2010 12
Multiple-Port S-parameters
Two-port S-parameter concept can be extended to multi-port
Required proper termination for other ports
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Bhaskar Banerjee, EE7V82 Spring 2010 13
S-parameters Measurement
S 11 = Reected Incident
=b
1a 1 a 2 = 0
S 21 =Transmitted
Incident =
b2
a 1 a 2 = 0
S 22 = Reected Incident =b
2a 2 a 1 = 0
S 12 =Transmitted
Incident =
b1
a 2 a 1 = 0
Incident TransmittedS 21
S 11Reflected
b 1
a 1
b 2
Z 0Load
a 2 = 0DUTForward
1IncidentTransmitted S 12
S 22Reflected
b 2
a 2
b
a 1 = 0
DUTZ 0Load Reverse
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Bhaskar Banerjee, EE7V82 Spring 2010 14
S-parameters Measurement
Equipment: Vector Network Analyzer (VNA)
Agilent PNA 2008
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Bhaskar Banerjee, EE7V82 Spring 2010 15
S-parameters Measurement
Vector Network Analyzer (VNA) operation
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Bhaskar Banerjee, EE7V82 Spring 2010 16
Smith Chart
Smith Chart maps rectilinear impedance plane onto polar plane
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Bhaskar Banerjee, EE7V82 Spring 2010 17
Smith Chart
Impedance plot over frequency
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Bhaskar Banerjee, EE7V82 Spring 2010 18
Device Characterization Parameters
Reflected
Incident
REFLECTION
SWR
S-ParametersS11,S22 Reflection
Coefficient
Impedance,Admittance
R+jX,G+jB
ReturnLoss
,
A
R=
Transmitted
Incident
TRANSMISSION
Gain / Loss
S-ParametersS21,S12
GroupDelay
TransmissionCoefficient
InsertionPhase
,
B
R=
R
A
Incident
Reflected
BTransmittedDUT
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Bhaskar Banerjee, EE7V82 Spring 2010 19
Device Characterization Parameters
Reection parameters S11 and S22 Reection coefcient ( ) Return Loss (RL) (dB) Voltage Standing Wave Ratio (VSWR)
E max
E min
Standing wave
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Bhaskar Banerjee, EE7V82 Spring 2010 20
Device Characterization Parameters
Transmission parameters S21 and S12 Transmission coefcient ( T ) Insertion Loss (IL) or Gain Group delay