Measuring the S-Parameters of a 50 to 75 Ohm impedance

Measuring the S-Parameters of a 50 to 75 Ohm impedance
Product: Vector Network Analyzer R&S®ZVA
Measuring the S-Parameters of a 50 to 75 Ohm
impedance matching device using the
Vector Network Analyzer ZVA
Application Note
This document describes how the advanced calibration techniques of the ZVA Vector
Network Analyzer can solve the challenges of measuring the S-Parameters on impedance
matching devices. The document describes the concept and setup required to perform the
calibration of the ZVA and making the measurement.
The procedure described in this application note applies to the ZVB and ZVT Vector
Network Analyzers as well.
Subject to change – Kenneth Rasmussen, 03.2009
Introduction
Contents
1.
2.
3.
4.
5.
6.
7.
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Introduction………………………………….. ….… 3
R&S RAM, Minimum Loss Pad……...………….. 4
Measurement Setup for the Minimum Loss Pad. 5
UOSM Calibration………………………………… 7
Measurement of R&S RAM……………………… 9
Additional Information……………………………. 10
Ordering Information……………………………… 10
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Introduction
1. Introduction
This document is designed to be a guide to help point the user in the right
direction for configuring the ZVA Vector Network Analyzer to make relevant
measurements on impedance matching devices like Minimum Loss Pads.
With the previous generation of Vector Network Analyzers, measurement of the
S-Parameters on impedance matching devices like Minimum Loss Pads (MLP)
was impossible. This is due to the fact that MLP’s have different impedances at
the Input and Output ports. Traditionally, VNA’s could not do a full 2-port
calibration with different impedances on the test ports. But with the arrival of the
ZVA generation of Vector Network Analyzers and the UOSM calibration method,
this is now possible.
This application will use the R&S RAM, a DC - 2.7 GHz 50C/75C Matching Pad
as the Device-Under-Test (DUT).
Due to limited or no availability of calibration kits in other than 50C and 75C
impedances, it is not practical to convert to other impedances.
For further information please refer to the internal help of the ZVA [HELP] or
alternatively you can access the help online at the Rohde & Schwarz website,
http://www.rohde-schwarz.com/webhelp/zva/start.htm
In this document:
•
Hardkeys are shown as
Softkeys are shown as
Windows buttons and tabs are shown as
Windows dialog box names are shown as
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[MODE]
[PRESET] [HELP]
[Start]
Set Power…
Set Powers
Rohde & Schwarz
R&S RAM, Minimum Loss Pad
2. R&S RAM, Minimum Loss Pad
The Minimum Loss Pad (or L-pads) can be used to perfectly match one
impedance to another, but the loss is high. In microwave engineering, this is
usually not acceptable; we'd rather match two impedances with near-zero loss
by using reactive components, which limits the bandwidth of the solution. In
instrumentation systems however, we normally prefer a frequency-independent
device like the MLP to do the impedance conversion. A typical application for
the MLP is when we want to measure TV signals in a 75 Ohm system with a
50C Spectrum Analyzer. Here the MLP will provide the proper matching
between the different impedances. However this comes at the expense of
additional power loss.
Note that for a given input and output impedance, only one solution exists for an
L-pad where the input and output are to be perfectly matched; this is what we
know as the Minimum Loss Pad.
R1
Z1
R2
Z2
Matching Pad
L-Pad matching network (Z1 > Z2)
The equations for calculating the values of R1 and R2 are simple to derive using
Ohm’s Law. For Z1 > Z2 the following applies:
R1 = Z1 1
Z2
Z1
R2 =
Z2
Z2
1
Z1
The attenuation (or insertion power loss) is defined as (Power Out)/(Power In):
Pout / Pin =
1
Z1
Z1
+
Z2
Z2 1
2
Please note, this is the linear value, not dB! The attenuation can be expressed
in dB as follows:
Attenuation(dB) = 10 Log 10
Pout
Pin
For the R&S RAM, which converts from 75C to 50C, the following values apply:
R1 = 43.3 C
R2 = 86.6 C
Attenuation (dB) = -5.7 dB
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Measurement Setup for the Minimum Loss Pad
3. Measurement Setup for the Minimum Loss Pad
To measure the S-Parameters of a Minimum Loss Pad, the following equipment
are required:
•
•
•
•
•
•
•
R&S ZVA
R&S ZCAN 50C
R&S ZCAN 75C
R&S RAM
AG 1250-0597*
PE 9350*
Test Port Cables
*) AG : Agilent Technologies
Vector Network Analyzer
Type-N 50C Calibration Kit, 3 GHz
Type-N 75C Calibration Kit, 3 GHz
Matching Pad, 50C/75C
Type-N(m) 50C to Type-N(f) 75C mech. Adapter
Type-N(f) 50C to Type-N(m) 75C mech. Adapter
2 required. Model depends on ZVA connectors
PE : Pasternack Enterprices
WARNING!
At first glance, 50C and 75C Type-N connectors looks identical, but be careful.
The center pin of the 75C connectors is thinner than the center pin of the 50C
connectors.
Special care should be taken when mating 75C devices. Inserting a 50C male
connector into a 75C female connector can result in damage of the 75C female
connector.
On the other hand, the 75C male connector cannot damage the 50C female
connector due to the thinner center pin.
Please note the difference on the center pin thickness between 75C (Upper)
and 50C (Lower) connectors.
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Measurement Setup for the Minimum Loss Pad
Make the following setup with the ZVA as preparation for the calibration.
Please note that the Port 1 reference plane must be 50! Type-N(f) and that
Port 2 reference plane must be 75! Type-N(m).
The 75! side of the RAM is a Type-N(f), so an additional 75! Type-N(m-m)
adapter are required to realize the 75! Type-N(m) reference plane on Port 2.
Test Port Reference Planes
Calibration Setup for the Minimum Loss Pad measurement
To configure the ZVA for the measurement, press the following keys:
[PRESET]
[START CENTER] [Start] 10 MHz
[STOP SPAN] [Stop] 2.7 GHz
[PWR BW AVG] [Power] 0 dBm
[PWR BW AVG] [Meas Bandwidth] [1 kHz]
[PWR BW AVG] [Average Factor] 10, [Average On]
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UOSM Calibration
4. UOSM Calibration
An adapter represents a through standard with unknown characteristics (in
particular, with unknown delay time/transmission phase). The analyzer can
perform a TOSM calibration with an unknown through, provided that it is
reciprocal (S21 = S12). The modified TOSM calibration is referred to as UOSM
(Unknown through – Open – Short – Match) calibration. It can be selected as
follows:
1.
If different connector types and/or impedances are assigned to the test
ports, the analyzer automatically replaces TOSM –> UOSM.
2.
If the same connector types are used but the appropriate through
standard is not defined, the analyzer also replaces TOSM –> UOSM.
3.
UOSM can be selected explicitly using [CAL] [Start Cal] [Other]....
After acquiring the calibration sweep data for the unknown through, the analyzer
automatically determines its delay time/transmission phase.
To start the ZVA calibration using UOSM, we just select a standard two port
TOSM calibration. Since the setup applies to condition 1) above, UOSM will
automatically be selected. Press the following keys:
[CAL] [Start Cal] [Two-Port P1 P2] [TOSM]
Configure Connector type and Calibration Kits as shown below:
Uncheck this
Press Next > to proceed with the calibration.
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UOSM Calibration
Please connect calibration standards as shown below, one by one, and click the
box to measure the standard.
Unknown Reciprocal Through
indicates that UOSM is being
used for the calibration.
Press Next > to proceed when all standards are measured.
No action is required in the following window. Just press Apply to complete the
calibration.
For a non-dispersive standard (Dispersive check box cleared), the Delay Time
can be determined unambiguously, provided that the transmission phase
difference between two consecutive sweep points is below 90 deg. In this case
it is sufficient to press Apply in order to calculate the system error correction
data and close the calibration wizard.
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Measurement of R&S RAM, Minimum Loss Pad
5. Measurement of R&S RAM, Minimum Loss Pad
Connect the device RAM to the calibrated reference planes of the ZVA as
shown below;
With the UOSM calibration performed in the previous section, we now have the
ZVA calibrated with Z0 = 50C on Port 1 and Z0 = 75C on Port 2. Note the marker
readings in the S11 and S22 Smith Chart plots below.
The marker readings for S21 and S12 also show expected measurement results
close to -5.7 dB power insertion loss in both directions.
Trc1 S11 Smith Ref 1 U
Cal
1
M11 1.355000 GHz
S11
0.5
2
49.481 C
j214.34 mC
25.176 pH
0
0.2
0.5
1
Cal
2
M1 1.355000 GHz -5.8041 dB
S21
10
M1
0
-10
5
M1
Trc2 S21 dB Mag 10 dB / Ref 0 dB
-20
2
-30
-40
-5
-0.5
-50
-60
-2
-70
-1
Ch1 Start 10 MHz
Pwr 0 dBm
Trc3 S12 dB Mag 10 dB / Ref 0 dB
S12
10
0
Stop 2.7 GHz
Cal
3
•M1 1.355000 GHz -5.8160 dB
Ch1
Start 10 MHz
Pwr 0 dBm
Trc4 S22 Smith Ref 1 U
Stop 2.7 GHz
Cal
4
M11 1.355000 GHz
S22
0.5
M1
2
-10
76.977 C
-j117.95 mC
995.85 pF
5
-20
0
-30
0.2
0.5
M1
1
2
-40
-5
-50
-60
-0.5
-70
Ch1 Start 10 MHz
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-2
-1
Pwr 0 dBm
9
Stop 2.7 GHz
Ch1
Start 10 MHz
Pwr 0 dBm
Stop 2.7 GHz
Rohde & Schwarz
Additional Information
6. Additional Information
This Application Note is updated from time to time. Please visit the
website www.rohde-schwarz.com to download the latest versions
Please send any comments or suggestions about this application note
to info.rsdk@rohde-schwarz.com.
7. Ordering Information
Listed are all R&S ZVA, R&S ZVB and R&S ZVT network analyzers. Of
course, accessories like test cables, or manual and automatic
calibration kits are available in addition. For details, please contact your
local R&S sales office, or the R&S web site.
Order No.
Type
Designation
1145.1110.08
R&S ZVA8
Vector Network Analyzer, 2 Ports, 8 GHz
1145.1110.10
R&S ZVA8
Vector Network Analyzer, 4 Ports, 8 GHz
1145.1110.24
R&S ZVA24
Vector Network Analyzer, 2 Ports, 24 GHz
1145.1110.26
R&S ZVA24
Vector Network Analyzer, 4 Ports, 24 GHz
1145.1110.40
R&S ZVA40
Vector Network Analyzer, 2 Ports, 40 GHz
1145.1110.42
R&S ZVA40
Vector Network Analyzer, 4 Ports, 40 GHz
1145.1110.50
R&S ZVA50
Vector Network Analyzer, 2 Ports, 50 GHz
1145.1110.52
R&S ZVA50
Vector Network Analyzer, 4 Ports, 50 GHz
1300.0000.08
R&S ZVT8
Vector Network Analyzer, 2 - 8 Ports, 8 GHz
1300.0000.20
R&S ZVT20
Vector Network Analyzer, 2 - 6 Ports, 20 GHz
1145.1010.04
R&S ZVB4
Vector Network Analyzer, 2 Ports, 4 GHz
1145.1010.06
R&S ZVB4
Vector Network Analyzer, 4 Ports, 4 GHz
1145.1010.08
R&S ZVB8
Vector Network Analyzer, 2 Ports, 8 GHz
1145.1010.10
R&S ZVB8
Vector Network Analyzer, 4 Ports, 8 GHz
1145.1010.14
R&S ZVB14
Vector Network Analyzer, 2 Ports, 14 GHz
1145.1010.19
R&S ZVB14
Vector Network Analyzer, 4 Ports, 14 GHz
1145.1010.20
R&S ZVB20
Vector Network Analyzer, 2 Ports, 20 GHz
1145.1010.25
R&S ZVB20
Vector Network Analyzer, 4 Ports, 20 GHz
0800.8515.52
R&S ZCAN
0 Hz to 3 GHz, 50@ Calibration Kit
0800.8515.72
R&S ZCAN
0 Hz to 3 GHz, 75@ Calibration Kit
ROHDE & SCHWARZ DENMARK A/S Ejby Industrivej 40, DK-2600 Glostrup, Denmark
Telephone +45 43436699 Fax +45 43437744 Internet: www.rohde-schwarz.dk
This application note and the supplied programs may only be used subject to the conditions of use set forth in the
download area of the Rohde & Schwarz website.
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