Measuring multiport devices with a two-port VNA with traceability to national standards Martin Salter 26 th ANAMET meeting 18 th September 2006
Measuring multiport devices with a two-port
VNA with traceability to national standards
Martin Salter
26th ANAMET meeting 18th September 2006
Overview
• Measurement Method for 3-ports
• Measurement of a 3-port directional coupler
• Measurement of a 3-port power splitter – with a short-circuit as termination
3-port directional coupler
Port 1
(female) Port 2
(male)
Port 3
(female)
Terminating
load
(permanently
attached)
Coupler measurands:
Coupling factor (dB)
Directivity (dB)
Magnitude of S11, S22 & S33
Measurement method (1)
• Method due to Speciale (MTT-30, 1982)
• Calibrate VNA with two male test ports (use LRL with female-female lines)
• Measure female-female adapter
Measurement method (2)
• Measure male and female loads
• De-embed adapter
VNA
Port 1
(male)
VNA
Port 2
(male)
(*) Adapter
(female-female)
Terminating
load
(male)
Terminating
load
(female)
Measurement method (3)
• Measure three partial 2-ports
(with the unused
port terminated with one of the
measured loads)
• De-embed adapters
VNA
Port 2
(male)
VNA
Port 1
(male)
(*) Adapter
(female-female) 1 2
3
Terminating
load
(male)
VNA
Port 1
(male)
VNA
Port 2
(male)
Ad
apte
r (*
)
(fem
ale
-fem
ale)
1
3
2
Terminating
load
(male)
VNA
Port 1
(male)
VNA
Port 2
(male)
1
2
3
Terminating
load
(female)
Measurement method (4)
• Renormalise scattering matrix of partial 2-ports to ZM at a male port and ZF at a female port
• Assemble 3-port scattering matrix normalised to ZM at male ports and ZF at female ports
• Renormalise 3-port scattering matrix to 50 ohms at all ports
• Calculate measurands from 3-port S-parameters
• Use a Monte Carlo method to propagate uncertainty from raw S-parameter measurements through adapter de-embedding and impedance renormalisation to measurands
Measurement of a 3-port directional coupler (1)
0.0000
0.0020
0.0040
0.0060
0.0080
0.0100
0.0120
0.0140
0.0160
0.0180
150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000
Frequency (MHz)
Lin
ea
r m
ag
nit
ud
e S
11
Measurement of a 3-port directional coupler (2)
0.0000
0.0020
0.0040
0.0060
0.0080
0.0100
0.0120
0.0140
0.0160
0.0180
150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000
Frequency (MHz)
Lin
ea
r m
ag
nit
ud
e S
22
Measurement of a 3-port directional coupler (3)
0.0000
0.0020
0.0040
0.0060
0.0080
0.0100
0.0120
0.0140
0.0160
0.0180
150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000
Frequency (MHz)
Lin
ea
r m
ag
nit
ud
e S
33
Measurement of a 3-port directional coupler (4)
19.000
19.500
20.000
20.500
21.000
21.500
22.000
22.500
23.000
23.500
24.000
150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000
Frequency (MHz)
Co
up
lin
g f
ac
tor
(dB
)
Measurement of a 3-port directional coupler (5)
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000
Frequency (MHz)
Dir
ec
tiv
ity
(d
B)
Measurement of a 3-port power splitter – with a short-circuit as termination (1)
• Renormalisation corrects for mismatch of terminating load
• If load is nominally matched correction should be small
• But what if termination is a high reflect e.g. a short-
circuit?
• Test of method
Measurement of a 3-port power splitter – with a short-circuit as termination (2)
1 2
3
VNA
PORT 1
VNA
PORT 1 VNA
PORT 1 VNA
PORT 2
VNA
PORT 2
VNA
PORT 2
1
2 3 1
2
3
First partial
two-port
Second partial
two-port
Third partial
two-port
Terminating load is either
nominally matched or else a
short-circuit
Power splitter measurands:
Input VSWR, effective output VSWR,
Output tracking (dB)
Measurement of a 3-port power splitter – with a short-circuit as termination (3)
0.94
0.95
0.96
0.97
0.98
0.99
1.00
1.01
1.02
1.03
1.04
1.05
0 5 10 15 20 25 30
Frequency (GHz)
Mag
nit
ud
e S
ho
rt-C
ircu
it V
RC
Measurement of a 3-port power splitter – with a short-circuit as termination (4)
-180
-135
-90
-45
0
45
90
135
180
0 5 10 15 20 25 30
Frequency (GHz)
Ph
as
e s
ho
rt-c
irc
uit
VR
C (
de
gre
es
)
Measurement of a 3-port power splitter – with a short-circuit as termination (5)
1
1.1
1.2
1.3
1.4
1.5
1.6
0 5 10 15 20 25 30
Frequency (GHz)
Inp
ut
VS
WR
at
po
rt 1
Short circuit
Matched load
Measurement of a 3-port power splitter – with a short-circuit as termination (6)
1
1.1
1.2
1.3
1.4
1.5
1.6
0 5 10 15 20 25 30
Frequency (GHz)
Eff
ec
tiv
e o
utp
ut
VS
WR
at
po
rt 2
SC
Matched load
Measurement of a 3-port power splitter – with a short-circuit as termination (7)
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
0 5 10 15 20 25 30
Frequency (GHz)
Eff
ec
tiv
e o
utp
ut
VS
WR
at
po
rt 3
Short circuit
Matched load
Measurement of a 3-port power splitter – with a short-circuit as termination (8)
-1.5
-1
-0.5
0
0.5
1
1.5
0 5 10 15 20 25 30
Frequency (GHz)
Ou
tpu
t T
rac
kin
g (
dB
)
Short circuit
Matched load