Network analyzers overview

1. Vector Network Analyzer 1
Introduction to Vector
Network Analyzer (VNA)

2. Vector Network Analyzer 2
• Introduction
• Transmission line basics
• Reflection and transmission parameters
• S parameter definition
Vector Network Analyzer (VNA)

3. Vector Network Analyzer 3
Introduction –
Types of Devices Tested by VNA
Device type Active
Passive
Integration
High
Low
Antennas
Switches
Multiplexers
Mixers
Samplers
Multipliers
Diodes
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
RFICs
MMICs
T/R modules
Transceivers
Receivers
Tuners
Converters
VCAs
Amplifiers
VCOs
VTFs
Oscillators
Modulators
VCAtten’s
Transistors

4. Vector Network Analyzer 4
• To verify specifications of building blocks in a
complex RF systems such as amplifiers and filters
in a transceiver
• Measured hardware prototype compared to
simulation model
• To ensure component or circuit cause no distortion
in the transmission of communications signals
• Linear : constant amplitude, linear phase /
constant group delay versus frequency
• Nonlinear : harmonics, intermodulation,
compression, AM-to-PM conversion
• To ensure good matching for absorbing energy
efficiently (such as good matching antenna)
Reasons for testing component

5. Vector Network Analyzer 5
Lightwave Analogy to RF Energy
RF
Incident
Reflected
Transmitted
Lightwave
DUT
• Network analysis is concerned with the accurate
measurement of the ratios of the reflected signal to the
incident signal, and the transmitted signal to the incident
signal.

6. Vector Network Analyzer 6
Transmission Line Basics
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 power transfer
 measured envelope voltage dependent on position along line
I
+ -

7. Vector Network Analyzer 7
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)
characteristic impedance
for coaxial airlines (ohms)
10 20 30 40 50 60 70 80 90 100
1.0
0.8
0.7
0.6
0.5
0.9
1.5
1.4
1.3
1.2
1.1
normalized
values
50 ohm standard
attenuation is lowest
at 77 ohms
power handling capacity
peaks at 30 ohms

8. Vector Network Analyzer 8
Power Transfer Efficiency
RS
RL
For complex impedances,
maximum power transfer occurs
when ZL = ZS* (conjugate
match)
Maximum power is transferred when RL = RS
RL / RS
0
0.2
0.4
0.6
0.8
1
1.2
0 1 2 3 4 5 6 7 8 9 10
Load
Power
(normalized)
R
s
R
L
+
j
X
-
j
X
For real impedances, maximum power
transfer occurs when RL = RS

9. Vector Network Analyzer 9
Transmission Line Terminated with Zo
For reflection, a transmission line terminated in Zo
behaves like an infinitely long transmission line
Zs = Zo
Zo
Vrefl = 0! (all the incident power
is absorbed in the load)
Vinc
Zo = characteristic impedance
of transmission line

10. Vector Network Analyzer 10
Transmission Line Terminated with
Short, Open
Zs = Zo
Vrefl
Vinc
For reflection, a transmission line terminated in a short or
open reflects all power back to source
In-phase (0o) for open,
out-of-phase (180o) for short

11. Vector Network Analyzer 11
Transmission Line Terminated with
25 W
Vrefl
Standing wave pattern does not go to zero as with
short or open
Zs = Zo
ZL = 25 W
Vinc

12. Vector Network Analyzer 12
High Freq. Device Characterization
Transmitted
Incident
TRANSMISSION
Gain / Loss
S-Parameters
S21, S12
Group
Delay
Transmission
Coefficient
Insertion
Phase
Reflected
Incident
REFLECTION
SWR
S-Parameters
S11, S22 Reflection
Coefficient
Impedance,
Admittance
R+jX,
G+jB
Return
Loss
G, r
T,t
Incident
Reflected
Transmitted
R
B
A
A
R
=
B
R
=

13. Vector Network Analyzer 13
Reflection Parameters
 dB
No reflection
(ZL = Zo)
r
RL
VSWR
0 1
Full reflection
(ZL = open, short)
0 dB
1 
=
ZL - ZO
ZL + O
Z
Reflection
Coefficient
=
Vreflected
Vincident
= r F
G
=
r G
Return loss, RL = -20 log (r),
VSWR =
Emax
Emin
=
1 + r
1 - r
Emax
Emin

14. Vector Network Analyzer 14
Transmission Parameters
V Transmitted
V Incident
Transmission Coefficient = T =
VTransmitted
VIncident
= t
DUT
Gain (dB) = 20 Log
V Trans
V Inc
= 20 log t
Insertion Loss (dB) = - 20 Log
V Trans
V Inc
= - 20 log t

15. Vector Network Analyzer 15
Smith Chart Review
 
Smith Chart maps
rectilinear impedance
plane onto polar plane
0 +R
+jX
-jX
Rectilinear impedance
plane
-90o
0
o
180
o
+
-
.2
.4
.6
.8
1.0
90
o

0
Polar plane
Z = Zo
L
= 0
G
Constant X
Constant R
Smith chart
G
L
Z = 0
= ±180
O
1
(short) Z =
L
= 0
O
1
G
(open)

16. Vector Network Analyzer 16
Characterizing Unknown Linear 2-port Devices
Using parameters (H, Y, Z, S) to characterize devices at low frequency:
 gives linear behavioral model of our device (or network)
 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 conditions
H-parameters
V1 = h11I1 + h12V2
I2 = h21I1 + h22V2
Y-parameters
I1 = y11V1 + y12V2
I2 = y21V1 + y22V2
Z-parameters
V1 = z11I1 + z12I2
V2 = z21I1 + z22I2
h11 = V1
I1 V2=0
h12 = V1
V2 I1=0
(requires short circuit)
(requires open circuit)
Extending measurements of these parameters to high frequencies is
not very practical !

17. Vector Network Analyzer 17
Why Use S-Parameters?
 relatively easy to obtain at high frequencies
 hard to measure total voltage & current at the device ports at high
frequency
 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 electronic-simulation
tools Incident Transmitted
S21
S11
Reflected S22
Reflected
Transmitted Incident
b1
a1
b2
a2
S12
DUT
b1 = S11a1 + S12 a2
b2 = S21 a1 + S22 a2
Port 1 Port 2

18. Vector Network Analyzer 18
Measuring S-Parameters
S 11 =
Reflected
Incident
=
b1
a 1 a2 = 0
S 21 =
Transmitted
Incident
=
b
2
a 1 a2 = 0
S 22 =
Reflected
Incident
=
b2
a 2 a1 = 0
S 12 =
Transmitted
Incident
=
b
1
a 2 a1 = 0
Incident Transmitted
S 21
S 11
Reflected
b 1
a1
b 2
Z0
Load
a2 = 0
DUT
Forward
Incident
Transmitted S 12
S 22
Reflected
b2
a2
b
a1 = 0
DUT
Z0
Load
Reverse
1

19. Vector Network Analyzer 19
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. They are expressed as real and imaginary or
magnitude and phase pairs
However, we often express them in a log magnitude format

20. Vector Network Analyzer 20
Network Analyzers Vs Spectrum Analyzers
.
Amplitude
Ratio
Frequency
Amplitud
e
Frequency
8563A
SPECTRUM ANALYZER 9 kHz - 26.5
GHz
Measures
known signal
Measures
unknown
signals
Network analyzers:
 measure components, devices,
circuits, sub-assemblies
 contain source and receiver
 display ratioed amplitude and phase
(frequency or power sweeps)
 offer advanced error correction
Spectrum analyzers:
 measure signal amplitude characteristics
carrier level, sidebands, harmonics...)
 can demodulate (& measure) complex signals
 are receivers only (single channel)
 can be used for scalar component test (no
phase) with tracking gen. or ext. source(s)

21. Vector Network Analyzer 21
Network Analyzer Hardware -
Generalized Network Analyzer Block
Diagram
RECEIVER / DETECTOR
PROCESSOR / DISPLAY
REFLECTED
(A)
TRANSMITTED
(B)
INCIDENT
(R)
SIGNAL
SEPARATION
SOURCE
Incident
Reflected
Transmitted
DUT

22. Vector Network Analyzer 22
Types of Network Analyzer
Scalar
• Magnitude only
• Broadband
Detector with higher
noise floor
• Lower Price
• Normalization –
Less Accurate
• Measures RL,
SWR, Gain/Loss
Vector
• Phase and Magnitude
• Tuned Detector with
lower noise floor
• Higher Price
• Complete Error
Correction – More
Accurate
• Measures all

23. Antenna Parameters 23
Basic Antenna
Parameters

24. 24
• Introduction
• Antenna - Reflection Coefficient / Return Loss ?
• Bandwidth
• VSWR
• Impedance Matching
• Other Parameters?  in class
• Demo and Hands On
Antenna Parameters
Antenna Parameters

25. 25
Introduction
Antenna Parameters

26. 26
Reflection Coefficient
If 50 % of the signal is absorbed by
the antenna and 50 % is reflected
back, we say that the Reflection
Coefficient. is -3dB. A very good
antenna might have a value of -
10dB (90 % absorbed & 10 %
reflected).
Antenna Parameters

27. 27
Bandwidth
Typically, bandwidth is
measured by looking at
SWR, i.e., by finding the
frequency range over which
the SWR is less than 2.
Bandwidth also can be measured by looking at the
frequency range where reflection coefficient value
dropped below than -10 dB.
Antenna Parameters

28. 28
VSWR
VSWR is a measure of impedance mismatch between the
transmission line and its load. The higher the VSWR, the
greater the mismatch. The minimum VSWR, i.e., that
which corresponds to a perfect impedance match, is unity.
The result is presented as a figure
describing the power absorption of
the antenna. A value of 2.0:1 VSWR,
which is equal to 90 % power
absorption, is considered very good
for a small antenna.
Antenna Parameters

29. 29
Impedance
An ideal antenna solution has an impedance of 50
ohm all the way from the transceiver to the antenna,
to get the best possible impedance match between
transceiver, transmission line and antenna. Since
ideal conditions do not exist in reality, the impedance
in the antenna interface often must be compensated
by means of a matching network, i.e. a net built with
inductive and/or capacitive components.
Antenna Parameters

30. 30
Hands On 1 - Antenna
Characteristic Measurements
You will be given few types of antennas, please
measure the following :
• Reflection Coefficient, S11
• VSWR
• 10 dB bandwidth and % bandwidth
• Impedance at resonance
Antenna Parameters

31. 31
Hands On 2 – Antenna
Measurement Environment
Display the S11 of your antenna between your frequency range of
interest. Place the marker at the minimum.
Observe the trace when the following objects are brought close to
it from different directions:
• metallic object (e.g. steel rule, metal rod)
• human hand
• insulator (e.g. book, plastic)
Observe the trace when the antenna is rotated by 90 degrees and
when it is moved around relative to surrounding.
Antenna Parameters