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Network Analyzer Basics
Network Analyzer Basics
Copyright
2000
Network Analysis is NOT.…
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Network Analyzer Basics
Copyright
2000
Low
Integration
High
What Types of Devices are Tested?
Duplexers
Diplexers
Filters
Couplers
Bridges
Splitters, dividers
Combiners
Isolators
Circulators
Attenuators
Adapters
Opens, shorts, loads
Delay lines
Cables
Transmission lines
Waveguide
Resonators
Dielectrics
R, L, C's
Passive
Network Analyzer Basics
RFICs
MMICs
T/R modules
Transceivers
Receivers
Tuners
Converters
VCAs
Amplifiers
Antennas
Switches
Multiplexers
Mixers
Samplers
Multipliers
Diodes
Device type
VCOs
VTFs
Oscillators
Modulators
VCAtten’s
Transistors
Active
Copyright
2000
Complex
Device Test Measurement Model
84000
RFIC test
Ded. Testers
VSA
Response
tool
SA
Harm. Dist.
LO stability
Image Rej.
VNA
SNA
NF Mtr.
NF
Imped. An.
LCR/Z
I-V
Measurement
plane
Absol.
Power
Gain/Flatness
Power Mtr.
Simpl
e
Full call
sequence
Pulsed S-parm.
Pulse profiling
Gain/Flat. Compr'n
Phase/GD AM-PM
Isolation
Rtn Ls/VSWR
Impedance
S-parameters
TG/SA
Param. An.
Intermodulation
Distortion
NF
BER
EVM
ACP
Regrowth
Constell.
Eye
Det/Scope
DC
CW
Swept Swept
freq
power
modulation
RF
Simple
Network Analyzer Basics
Noise
2-tone
Multi-
Stimulus type
Complex
tone
Pulsed-
Protocol
Complex
Copyright
2000
Lightwave Analogy to RF Energy
Incident
Reflected
Transmitted
Lightwave
DUT
RF
Network Analyzer Basics
Copyright
2000
Why Do We Need to Test Components?
• Verify specifications of “building blocks” for more
complex RF systems
• Ensure distortionless transmission
of communications signals
– linear: constant amplitude, linear phase / constant group
delay
– nonlinear: harmonics, intermodulation, compression, AMto-PM conversion
• Ensure good match when absorbing
power (e.g., an antenna)
F
M
9
7
K
P
W
R
Network Analyzer Basics
Copyright
2000
The Need for Both Magnitude and Phase
S21
1. Complete
characterization of
linear networks
S11
S22
S12
2. Complex impedance
needed to design
matching circuits
4. Time-domain
characterization
Mag
3. Complex values
needed for device
modeling
High-frequency transistor model
Time
5. Vector-error correction
Error
Base
Collector
Emitter
Network Analyzer Basics
Measured
Actual
Copyright
2000
Transmission Line Basics
+
I
-
Low frequencies
wavelengths >> wire length
current (I) travels down wires easily for efficient
power transmission
measured voltage and current not dependent on
position along wire
High frequencies
wavelength or << length of transmission
medium
need transmission lines for efficient power
transmission
matching to characteristic impedance (Zo) is
very important for low reflection and maximum
Network Analyzer Basics
power transfer
Copyright
2000
Transmission line Zo
•
•
Zo determines relationship between voltage and current
waves
Zo is a function of physical dimensions and r
Zo is usually a real impedance (e.g. 50 or 75 ohms)
1.5
attenuation is
lowest at 77 ohms
1.4
1.3
1.2
normalized values
•
1.1
50 ohm standard
1.0
0.9
0.8
0.7
power handling capacity
peaks at 30 ohms
0.6
0.5
10
20
30
40
50
60 70 80 90 100
characteristic impedance
for coaxial airlines (ohms)
Network Analyzer Basics
Copyright
2000
Power Transfer Efficiency
RS
For complex impedances, maximum
power transfer occurs when ZL = ZS*
(conjugate match)
RL
R
s
+
j
X
Load Power
(normalized)
1.2
1
j
X
0.8
0.6
R
L
0.4
0.2
0
0
1
2
3
4
5
6
7
8
9
10
RL / RS
Maximum power is transferred when RL = RS
Network Analyzer Basics
Copyright
2000
Transmission Line Terminated with Zo
Zs = Zo
Zo = characteristic
impedance
of
transmission line
Zo
Vinc
Vrefl = 0! (all the incident power
is absorbed in the load)
For reflection, a transmission line
terminated in Zo behaves like an infinitely
long transmission line
Network Analyzer Basics
Copyright
2000
Transmission Line Terminated with
Short, Open
Zs = Zo
Vinc
Vrefl
Network Analyzer Basics
In-phase (0o) for open,
out-of-phase (180o) for short
For reflection, a transmission line
terminated in a short or open reflects
all power back to source
Copyright
2000
Transmission Line Terminated with 25 W
Zs = Zo
ZL = 25 W
Vinc
Vrefl
Network Analyzer Basics
Standing wave pattern
does not go to zero as
with short or open
Copyright
2000
High-Frequency Device Characterization
Incident
Transmitted
R
B
Reflected
A
TRANSMISSION
REFLECTION
Reflected
Incident
=
SWR
S-Parameters
S11, S22
Reflection
Coefficient
G, r
Network Analyzer Basics
A
Transmitted
R
Incident
Return
Loss
Impedance,
Admittance
R+jX,
G+jB
=
B
R
Group
Delay
Gain / Loss
S-Parameters
S21, S12
Transmission
Coefficient
T,t
Insertion
Phase
Copyright
2000
Reflection Parameters
Reflection
Coefficient
G
Vreflected
=
=
Vincident
Return loss = -20 log(r),
r
r
F
=
ZL - ZO
Z L + ZO
G
=
Emax
Emin
Voltage Standing Wave
Ratio
Emax
VSWR =
Emin
=
1+r
1-r
Full reflection
(ZL = open, short)
No reflection
(ZL = Zo)
0
r
1
dB
RL
0 dB
1
VSWR
Network Analyzer Basics
Copyright
2000
Smith Chart Review
.
+jX
Polar plane
90
o
1.0
.8
.6
0
+R
.4
+ 180 o
-
o
.2
0
0
-jX
-90 o
Rectilinear impedance
plane
Constant X
Constant R
Z L = Zo
Smith Chart maps
rectilinear
impedance
plane onto polar
plane
Network Analyzer Basics
G=
0
G= 1
±180
(open)
ZL =
Z L = 0 (short)
G =1
O
0
Smith chart
Copyright
2000
O
Transmission Parameters
V Incident
DUT
Transmission Coefficient =
T
V
=
Trans
Insertion Loss (dB) = - 20 Log
V
V
Gain (dB) = 20 Log
V
Network Analyzer Basics
Trans
V Transmitted
V Transmitted
V Incident
= - 20 log
=
t
t
Inc
= 20 log
t
Inc
Copyright
2000
Linear Versus Nonlinear Behavior
A * Sin 360o * f (t - to)
A
Linear behavior:
Time
to
Sin 360o * f * t
A
Time
f
1
DUT
Input
phase shift =
to * 360o * f
input and output frequencies are
the same (no additional
frequencies created)
output frequency only undergoes
magnitude and phase change
Frequency
Output
Nonlinear behavior:
f
1
Frequency
Time
f
Network Analyzer Basics
1
Frequency
output frequency may
undergo frequency shift
(e.g. with mixers)
additional frequencies
created (harmonics,
intermodulation)
Copyright
2000
Criteria for Distortionless Transmission
Linear Networks
Linear phase over
bandwidth of
interest
Magnitude
Constant amplitude over
bandwidth of interest
Phase
Frequency
Frequency
Network Analyzer Basics
Copyright
2000
Magnitude Variation with Frequency
F(t) = sin wt + 1/3 sin 3wt + 1/5 sin 5wt
Time
Time
Magnitude
Linear
Network
Frequency
Network Analyzer Basics
Frequency
Frequency
Copyright
2000
Phase Variation with Frequency
F(t) = sin wt + 1 /3 sin 3wt + 1 /5 sin 5wt
Linear Network
Time
Magnitude
Time
Frequency
0°
Frequency
-180°
Frequency
-360 °
Network Analyzer Basics
Copyright
2000
Deviation from Linear Phase
Use electrical delay to
remove linear portion of
phase response
Linear electrical length
added
Phase 45 /Div
RF filter response
Deviation from linear
phase
o
o
Phase 1 /Div
(Electrical delay function)
+
Frequency
Low resolution
Network Analyzer Basics
yields
Frequency
Frequency
High resolution
Copyright
2000
Group Delay
Frequencyw
tg
Group delay ripple
Dw
to
Phase
Average delay
D
Frequency
Group Delay (tg) =
-d
dw
w
=
-1
360 o
*
d
df
in radians
in radians/sec
group-delay ripple indicates phase distortion
average delay indicates electrical length of DUT
aperture of measurement is very important
in degrees
f in Hertz (w = 2 p f)
Network Analyzer Basics
Copyright
2000
Phase
Phase
Why Measure Group Delay?
f
f
-d
dw
Group
Delay
Group
Delay
-d
dw
f
f
Same p-p phase ripple can result in different
group delay
Network Analyzer Basics
Copyright
2000
Characterizing Unknown Devices
Using parameters (H, Y, Z, S) to characterize
devices:
gives linear behavioral model of our device
measure parameters (e.g. voltage and current) versus
frequency under
various source and load conditions
(e.g. short and open circuits)
compute device parameters from measured data
predict
circuit performance
under any source
and load
H-parameters
Y-parameters
Z-parameters
conditions
V1 = h11I1 + h12V2
I1 = y11V1 + y12V2
V1 = z11I1 + z12I2
I2 = h21I1 + h22V2
Network Analyzer Basics
I2 = y21V1 + y22V2
V2 = z21I1 + z22I2
h11 = V1
I1
V2=0
(requires short circuit)
h12 = V1
V2
I1=0
(requires open circuit)
Copyright
2000
Why Use S-Parameters?
relatively easy to obtain at high frequencies
measure voltage traveling waves with a vector network analyzer
don't need shorts/opens which can cause active devices to oscillate
or self-destruct
relate to familiar measurements (gain, loss, reflection coefficient ...)
can cascade S-parameters of multiple devices to predict system
performance
can compute H, Y, or Z parameters from S-parameters if desired
can easily import and use S-parameter files in our electronicsimulation tools
a1
S 21
Incident
b2
S11
Reflected
b1
Transmitted
DUT
Port 1
Transmitted
Port 2
S12
S22
Reflected
a2
Incident
b1 = S11 a1 + S12 a 2
b 2 = S21 a1 + S22 a 2
Network Analyzer Basics
Copyright
2000
Measuring S-Parameters
a1
Forward
S 21 =
b1
Incident
a2 = 0
b1
= a
1
b
a2 = 0
Z0
a2 = 0
DUT
Load
Network Analyzer Basics
S 22 =
2
= a
1
a1 = 0
b1
Load
DUT
Reflected
Transmitted
b2
Transmitted
21
Z0
S 11
Reflected
Incident
S 11 =
S
Incident
Transmitted
S 12
S 12 =
Reflected
Incident
Transmitted
Incident
S 22
b2
= a
2
b
a1 = 0
1
= a
2
a1 = 0
b2
Reverse
Reflected
a2
Incident
Copyright
2000
Equating S-Parameters with Common
Measurement Terms
S11 = forward reflection coefficient (input match)
S22 = reverse reflection coefficient (output match)
S21 = forward transmission coefficient (gain or loss)
S12 = reverse transmission coefficient (isolation)
Remember, S-parameters are inherently
complex, linear quantities -- however, we
often express them in a log-magnitude
format
Network Analyzer Basics
Copyright
2000
Criteria for Distortionless Transmission
Nonlinear Networks
•
•
Saturation, crossover,
intermodulation, and other nonlinear
effects can cause signal distortion
Effect on system depends on amount
and type of distortion and system
architecture
Time
Frequency
Network Analyzer Basics
Time
Frequency
Copyright
2000
Measuring Nonlinear Behavior
Most common measurements:
using a network analyzer and
power sweeps
gain compression
AM to PM conversion
using a spectrum analyzer +
source(s)
harmonics, particularly second
and third
intermodulation products resulting
from two or more RF
carriers
8563A
LPF
LPF
Network Analyzer Basics
SPECTRUM ANALYZER
RL 0 dBm
ATTEN
10 dB
10 dB / DIV
9 kHz - 26.5 GHz
DUT
CENTER 20.00000 MHz
RB 30 Hz
VB 30 Hz
SPAN 10.00 kHz
ST 20 sec
Copyright
2000
What is the Difference
Between Network and
Spectrum Analyzers?
.
Measures
known
signal
Amplitude
Amplitude Ratio
8563A
measure components,
devices,
circuits, sub-assemblies
contain source and receiver
display ratioed amplitude and
phase
(frequency or power sweeps)
offer advanced error
Network
Analyzer Basics
correction
9 kHz - 26.5
Measures
unknown
signals
Frequency
Network analyzers:
SPECTRUM ANALYZER
GHz
Frequency
Spectrum analyzers:
measure signal amplitude
characteristics
carrier level, sidebands,
harmonics...)
can demodulate (& measure)
complex signals
are receivers only (single channel)
Copyright
can be used for scalar component
2000
test (no
Generalized Network Analyzer
Block Diagram
Incident
Transmitted
DUT
SOURCE
Reflected
SIGNAL
SEPARATION
INCIDENT
(R)
REFLECTED
(A)
TRANSMITTED
(B)
RECEIVER / DETECTOR
PROCESSOR / DISPLAY
Network Analyzer Basics
Copyright
2000
Source
Supplies stimulus for system
Swept frequency or power
Traditionally NAs used separate
source
Most Agilent analyzers sold
today have integrated,
synthesized sources
Network Analyzer Basics
Copyright
2000
Incident
Signal Separation
Transmitted
DUT
Reflected
SOURCE
SIGNAL
SEPARATION
INCIDENT (R)
REFLECTED
(A)
TRANSMITTED
(B)
RECEIVER / DETECTOR
PROCESSOR / DISPLAY
•
•
measure incident signal for reference
separate incident and reflected signals
splitter
bridge
directional
coupler
Network Analyzer Basics
Detector
Test Port
Copyright
2000
Directivity
Directivity is a measure of how well a
coupler can separate signals moving
in opposite directions
(undesired leakage
signal)
(desired reflected
signal)
Test port
Directional Coupler
Network Analyzer Basics
Copyright
2000
Interaction of Directivity with the
DUT (Without Error Correction)
0
Device
Return Loss
Directivity
Data Max
DUT RL = 40 dB
30
Add in-phase
60
Network Analyzer Basics
Device
Device
Directivity
Frequency
Data Min
Add out-of-phase
(cancellation)
Data = Vector Sum
Directivity
Copyright
2000
Incident
Detector Types
Transmitted
DUT
Reflected
SOURCE
Diode
Scalar broadband
(no phase
information)
SIGNAL
SEPARATION
INCIDENT (R)
REFLECTED
(A)
TRANSMITTED
(B)
RECEIVER / DETECTOR
PROCESSOR / DISPLAY
DC
RF
AC
Tuned Receiver
IF = F LO F RF
RF
ADC / DSP
Vector
(magnitude and
phase)
IF Filter
LO
Network Analyzer Basics
Copyright
2000
Broadband Diode Detection
Easy to make broadband
Inexpensive compared to tuned receiver
Good for measuring frequency-translating devices
Improve dynamic range by increasing power
Medium sensitivity / dynamic range
10 MHz
Network Analyzer Basics
26.5 GHz
Copyright
2000
Narrowband Detection - Tuned Receiver
ADC / DSP
Best sensitivity / dynamic range
Provides harmonic / spurious signal
rejection
Improve dynamic range by increasing
power, decreasing IF bandwidth, or
averaging
Trade off noise floor and
measurement speed
10 MHz
Network Analyzer Basics
26.5 GHz
Copyright
2000
Comparison of Receiver Techniques
Broadband
(diode)
detection
0 dB
0 dB
-50 dB
-50 dB
-100 dB
-100 dB
-60 dBm Sensitivity
higher noise floor
false responses
Narrowband
(tuned-receiver)
detection
< -100 dBm Sensitivity
high dynamic range
harmonic immunity
Dynamic range = maximum receiver power receiver noise floor
Network Analyzer Basics
Copyright
2000
Dynamic Range and Accuracy
Error Due to Interfering Signal
100
-
Error (dB, deg)
10
+
Dynamic range
is very important
for measurement
accuracy!
phase error
1
magn error
0.1
0.01
0.001
0
-5
-10
-15
-20
-25
-30
-35
-40
-45
-50
-55
-60
-65
-70
Interfering signal (dB)
Network Analyzer Basics
Copyright
2000
T/R Versus S-Parameter Test Sets
S-Parameter Test Set
Transmission/Reflection Test Set
Source
Source
Source
Transfer switch
Transfer switch
R1
R
R
B
A
B
A
R2
Port 1
Port 2
Port 2
Port 2
Port 1
Port 1
Fwd
RF always comes out port
1
port 2 is always receiver
response, one-port cal
Network Analyzer Basics
available
Fwd
DUT
DUT
Rev
RF comes out port 1 or port
2
forward and reverse
measurements
Copyright
two-port calibration 2000
Processor / Display
Incident
Transmitted
DUT
50 MH-20GHz
NETWORK ANYZER
ACTIVE
CHANNEL
Reflected
CH2 START 775.000 000 MHz
CH1 START 775.000 000 MHz
SOURCE
ENTRY
STOP 925.000 000 MHz
STOP 925.000 000 MHz
Hld
RESPONSE
PASS
2
Cor
PRm
SIGNAL
SEPARATION
880.435 000 MHz
1
PASS
Hld
1
STIMULUS
R CHANNEL
INSTRUMENT
STATE
1
Cor
INCIDENT
(R)
REFLECTED
(A)
TRANSMITTED
(B)
PRm
T
Duplexer Test - Tx-Ant and Ant-Rx
839.470 000 MHz
CH2
CH1
S12
S21
log MAG
log MAG
10 dB/
10 dB/
REF 0 dB
REF 0 dB
PORT 1
1_ -1.2468 dB
1_ -1.9248 dB
HP-IB STATUS
PORT 2
RECEIVER / DETECTOR
PROCESSOR / DISPLAY
CH2 START 775.000 000 MHz
CH1 START 775.000 000 MHz
STOP 925.000 000 MHz
STOP 925.000 000 MHz
Hld
PASS
2
Cor
markers
limit lines
pass/fail indicators
linear/log formats
grid/polar/Smith
charts
Network Analyzer Basics
PRm
880.435 000 MHz
1
PASS
Hld
1
1
Cor
PRm
Duplexer Test - Tx-Ant and Ant-Rx
839.470 000 MHz
CH2
CH1
S12
S21
log MAG
log MAG
10 dB/
10 dB/
REF 0 dB
REF 0 dB
1_ -1.2468 dB
1_ -1.9248 dB
Copyright
2000
R L
S
Frequency Sweep - Filter Test
CH1 S 21
log MAG
10 dB/
REF 0 dB
CH1 S11
log MAG
5 dB/
REF 0 dB
Cor
Stopba
nd
rejectio
n
69.1 dB
START .300 000 MHz
STOP 400.000 000 MHz
CH1 S21
SPAN 50.000 MHz
CENTER 200.000 MHz
log MAG
1 dB/
REF 0 dB
Return loss
Cor
1
4.000 000
GHz -
m1:
0.16 dB
m2-ref: 2.145 234 GHz
0.00 dB
ref
2
Insertion lossCor
x2 1
START 2 000.000 MHz
Network Analyzer Basics
2
STOP 6 000.000 MHz
Copyright
2000
Output Power (dBm)
Power Sweeps - Compression
Saturated output
power
Compression
region
Linear region
(slope = small-signal gain)
Input Power (dBm)
Network Analyzer Basics
Copyright
2000
Power Sweep - Gain Compression
CH1 S21
1og MAG
1 dB/ REF 32 dB
30.991 dB
12.3 dBm
1 dB
compression:
1
0
START -10 dBm
Network Analyzer Basics
CW 902.7 MHz
input power
resulting in 1 dB
drop in gain
STOP 15 dBm
Copyright
2000