Mixer Measurements with ZVA-K4

Mixer Measurements with ZVA-K4
Product: Vector Network Analyzer R&S®ZVA
Performing Mixer Measurements with the
Vector Network Analyzer ZVA
+
ZVA-K4 Frequency Conversion option
Application Note
This document describes the typical measurements performed on mixers and how they
can be implemented on the ZVA Vector Network Analyzer with the ZVA-K4 Frequency
Conversion option. The document describes the concept and setups required to perform
Conversion Loss, Isolation, Intermodulation and Reflection measurements.
Subject to change – Kenneth Rasmussen, 03.2009
Introduction
Contents
1.
2.
3.
4.
5.
6.
7.
Introduction………………………………….. ….… 3
Conversion Loss Measurements……………….. 3
Conversion Loss Measurement Setup……….… 4
RF to IF Conversion Loss Measurement…….… 5
RF Input Compression Measurement………….. 8
Conversion Loss vs. LO Power Measurement… 10
Power calibration for Conversion Loss……….… 12
8.
9.
10.
11.
12.
13.
14.
Isolation Measurements…………………………. 16
Isolation Measurement Setup…………………… 16
Arbitrary Port Configuration……………………… 17
RF to IF Isolation Measurement………………… 17
LO to IF Isolation Measurement………………… 20
LO to RF Isolation Measurement……………….. 22
Power Calibration for Isolation Measurements… 23
15. RF and LO port Return Loss Measurements….. 26
16. Intermodulation Measurements…………………. 29
17. Additional Information……………………………. 35
18. Ordering Information……………………………… 35
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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 and ZVT Vector Network Analyzers to make
relevant measurements on mixers.
Please note that the measurements in this document will refer to the ZVA only,
but is valid for the ZVT as well.
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
[MODE]
[PRESET] [HELP]
[Start]
Set Power…
Set Powers
The examples and setups shown in this application note are valid for firmware
version 2.50 and higher. The examples are not tested on earlier versions, but
should be working for these as well.
2. Conversion Loss Measurements
Conversion Loss (or Gain) is a measure of the power change when the Mixer is
converting the RF frequency to the IF frequency. It is defined as the ratio
between the Pout (IF) level and the Pin (RF) level and is expressed in dB.
Conversion measurements can be performed as a function of both frequency
and amplitude.
Typical Conversion measurements on a mixer include:
•
•
•
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Conversion Loss / Gain over frequency range of interest.
Mixer dynamic range / compression of the RF input signal.
Conversion Loss / Gain as a function of LO power level.
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Conversion Loss Measurement Setup
3. Conversion Loss Measurement Setup
To characterize the conversion loss / gain as a function of either frequency or
amplitude, the mixer should be connected to port 1, 2 and 3 of a 4-port ZVA with
option ZVA-K4, as indicated below (left). The 4-port ZVA has two internal
generators allowing the simultaneous feed of both the RF and LO signals.
If a 4-port ZVA is not available, then a 2-port ZVA and an external RF Signal
Generator can be used, as indicated below (right).
The Signal Generator will be controlled by the ZVA using a USB-GPIB interface
(option ZVAB-B44). Signal Generators like the SMF/SMA/SMB etc. can be
controlled with the LAN interface as well. The reference frequencies of the ZVA
and the Signal Generator must be locked to each other. Both the ZVA and the
Signal Generator can be the master.
The RF Signal Generator will then provide the Local Oscillator signal for the
mixer.
ROHDE&SCHWARZ
IEEE Bus
Ref-Frequency
Please note that the conversion loss measurements and
power calibration discussed in chapters 3 to 7 also
applies to the ZVB with option K3. The ZVB however
uses a different port connection to the mixer.
ZVA 24 VECTOR NETWORK ANALYZER 10 MHz …
24 GHz
1
2
RF
IF
LO
To configure an external Signal Generator, press [SYSTEM CONFIG], then
[System Config] softkey. Select the External Generators tab to configure the
Signal Generator.
If you want to use a Signal Generator not supported by the ZVA driver library,
then contact your Rohde & Schwarz sales representative for information about
adding new Signal Generator drivers to your ZVA.
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Configure a Conversion Loss Measurement
In the following examples, we will examine a passive mixer in the RF frequency
range 1.3 to 1.6 GHz with a fixed IF frequency of 70 MHz.
First we will configure the ZVA for measuring the RF to IF Conversion Loss.
RF to IF Conversion Loss (or Gain) can be defined as:
Pout (fIF)
Conversion Loss (dB) = 10 log ---------------Pin (fRF)
4. RF to IF Conversion Loss Measurement
Press [PRESET]
To start the configuration, press [MODE], then [Scalar Mixer Meas
[Define Scalar Mixer Meas] softkeys. The following menu will appear.
] and
On the ZVA, port 1 and 2 are already defined to be used for the mixer RF and IF
ports. First step is selecting the source for the LO signal. This can be either port
3, port 4 or an External Generator. On a 4-port ZVA, we select port 3.
Next we can select Set Powers… and Set Frequencies… to configure the actual
measurement.
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RF to IF Conversion Loss Measurement
In the Set Frequencies menu, we select:
RF Frequency
IF Frequency
LO Frequency
= Swept
= Fixed
= Auto
We must also select the type of Conversion required. In this case we have
selected IF = LO – RF (LSB), which will give us a LO frequency above the RF
frequency.
Then we configure the Start and Stop frequencies. This can also be done using
the [START] and [STOP] keys before entering the Mixer configuration menu.
Finally we define the fixed IF frequency. In the Fixed Frequency: IF field, enter
70 MHz
In the Set Powers menu, we enter the appropriate power levels for the RF signal
and the LO signal.
The CW Power level should be selected so that the Mixer is not driven into
compression, in this case we use -10 dBm.
The Fixed Power:LO level must be sufficiently high to properly bias the mixer
diodes, here we use +7 dBm.
Please note that the ZVA is capable of providing very high power levels,
typically >15 dBm directly from the test port. This is more than enough to drive
the LO port on almost any type of mixer and overcome the losses caused by
additional cabling of filters, matching pads, etc.
When leaving the Define Scalar Mixer Measurement menu by pressing OK, the
ZVA will enable the Mixer measurement configuration.
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RF to IF Conversion Loss Measurement
Please note that we do not measure S-parameters here. Instead we measure
the (b2/a1) wave quantity ratio. This is due to the fact that the two wave
quantities are at different frequencies.
b2/a1: Conversion Loss
(a1) is the RF incident power wave or reference power sweeping from 1.3 to 1.6
GHz. (b2) is the transmitted IF power wave or measured power at 70 MHz.
Trc1 b2/a1 dB Mag 10 dB / Ref 0 dB
1 of 3 (Max)
• M 1 1.450000 GHz -4.9953 dB
b2/a1
10
0
M1
-10
-20
-30
-40
-50
-60
-70
Ch1 Mix Frq RF Start 1.3 GHz
Pwr -10 dBm
Stop 1.6 GHz
The measurement plot shows a conversion loss value of about 5 dB, which is
expected for these kind of passive mixers.
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RF Input Compression Measurement
5. RF Input Compression Measurement
In the RF Input Compression measurement, we will setup a RF power sweep at
1.5 GHz and measure the Mixers Conversion Loss as a function of the RF Input
power level. This measurement will then enable us to determine the upper limit
of the Mixers linear dynamic range.
To start the configuration:
Press [CHAN SELECT], then [Add Channel + Trace + Diag Area] softkey. This
will create a second channel in a new diagram area, which is identical to the first
channel.
Hint: Double-clicking in the diagram area of a window will expand the window to
full screen. Double-clicking again will show all configured windows. This can
also be done by pressing [AREA SELECT], then use [Maximize] and [Split All]
softkeys.
Press [SWEEP], then [Sweep Type
Power Sweep mode on channel 2.
] and [Power] softkeys. The ZVA is now in
Press [START CENTER], then [CW Frequency] softkey. Enter 1.5 GHz.
Press [MEAS], then [Ratios
] and [b2/a1 Src Port 1] softkeys.
Press [MODE], then [Scalar Mixer Meas] and [Define Scalar Mixer Meas]
softkeys to enter the Scalar Mixer configuration menu. Then press Set Powers
to enter the Power configuration menu.
Please note that the Set Powers dialog box has changed to reflect that the
channel is now setup to do Power Sweep instead of Frequency Sweep.
Make sure that the Enter & Display field is set to RF Source, then type in the
Start Power = -25 dBm and Stop Power = +12 dBm. Also make sure that the
Fixed Power: LO is still +7 dBm.
Press OK and OK to exit the Scalar Mixer configuration menu and view the
measurement result.
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RF Input Compression Measurement
b2/a1: Conversion Loss
a1:
RF Power in
b2;
IF Power out
The measurement plot Trc2 (b2/a1) shows a conversion loss value of about 5
dB as long as the Mixer operates in its linear input range. At about 0 dBm, we
can see that the Mixer is reaching its compression point and that the conversion
loss is increasing.
Additional traces can be added to the channel if you want to examine the (a1,
RF power) and (b2, IF power) wave quantities. See Trc3 and Trc4 in the plot
below.
Trc2 b2/a1 dB Mag 10 dB / Ref 0 dB
Trc3 a1
dB Mag 10 dB / Ref 0 dBm
Trc4 b2
dB Mag 10 dB / Ref 0 dBm
2 of 3 (Max)
b2/a1
10
0
Cmp
-10
•Trac Stat: Trc2 b2/a1
Cmp In:
1.2 dBm
Cmp Out:
-4.5 dBm
-20
-30
-40
-50
-60
-70
Ch2 Mix Pwr RF Start -25 dBm
Freq 1.5 GHz
Stop 12 dBm
By using the ZVA’s trace statistics capabilities, it can automatically search for
the compression point. Furthermore it will provide information about the
absolute input and output power levels at the compression point. To enable this
press:
[TRACE FUNCT], then [Trace Statistics
] and [Compression Point] softkeys.
Default compression value is 1 dB, but can be changed by pressing the [Define
Compression Value] softkey and enter a different value.
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Conversion Loss vs. LO Power Measurement
6. Conversion Loss vs. LO Power Measurement
Another important measurement is the Mixer Conversion Loss as a function of
the LO Power. Minimum Conversion Loss is obtained when the LO power level
can properly bias the Mixer diodes.
To start the configuration:
Make sure that channel 2 from the previous measurement is active.
Please note that when a new channel is created, the settings from the current
active channel are copied to the new channel. This avoids configuring the new
channel from scratch.
Press [CHAN SELECT], then [Add Channel + Trace + Diag Area] softkey. This
will create a third channel in a new diagram area, which is identical to the
second channel.
Press [MEAS], then [Ratios
] and [b2/a1 Src Port 1] softkeys.
Press [MODE], then [Scalar Mixer Meas] and [Define Scalar Mixer Meas]
softkeys to enter the Scalar Mixer configuration menu. Then press Set Powers
to enter the Power configuration menu.
Change the Enter & Display field so that it is set to LO Source. Now we can
sweep the LO source power and use a fixed power level for the RF. Then type
in Start Power = -25 dBm and Stop Power = +12 dBm.
In the Fixed Power: RF field, enter -10 dBm.
Press OK and OK to exit the Scalar Mixer configuration menu and view the
measurement result.
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Conversion Loss vs. LO Power Measurement
The measurement plot (Trc5) shows that at low LO power levels, the conversion
loss is large. At levels above 0 dBm we can see that the trace is flattened out,
indicating that the mixer diodes are properly biased.
Trc5 b2/a1 dB Mag 10 dB / Ref 0 dB
Trc6 b2
dB Mag 10 dB / Ref 0 dBm
Trc7 a3
dB Mag 10 dB / Ref 0 dBm
3 of 3 (Max)
b2/a1
10
b2/a1: Conversion Loss
a3:
LO Power in
b2;
IF Power out
0
-10
-20
-30
-40
-50
-60
-70
Ch3 Mix Pwr LO Start -25 dBm
Freq 1.5 GHz
Stop 12 dBm
By splitting the windows we have configured so far using [AREA SELECT] and
[Split All], we now have the full overview of the configured conversion loss
measurements. This is shown in the picture below.
Trc1 b2/a1 dB Mag 10 dB / Ref 0 dB
b2/a1
10
0
1
•M1 1.450000 GHz -5.0354 dB
M1
b2/a1
10
0
-10
-20
-30
-40
-50
-60
-70
-10
-20
-30
-40
-50
-60
Conversion Loss
-70
Ch1 Mix Frq RF Start 1.3
PwrGHz
-10 dBm
Stop 1.6 GHz
Trc5 b2/a1 dB Mag 10 dB / Ref 0 dB
Trc7 a3
dB Mag 10 dB / Ref 0 dBm
Trc2 b2/a1 dB Mag 10 dB / Ref 0 dB
Trc3 a1
dB Mag 10 dB / Ref 0 dBm
Trc4 b2
dB Mag 10 dB / Ref 0 dBm
2
Cmp
Trac Stat: Trc2 b2/a1
Cmp In:
1.3 dBm
-4.5 dBm
Cmp Out:
Mixer Compression
Ch2 Mix Pwr RF Start -25
FreqdBm
1.5 GHz
Trc6 b2 dB Mag 10 dB / Ref 0 dBm
Stop 12 dBm
3
b2/a1
10
0
-10
-20
-30
-40
-50
-60
Conversion Loss vs. LO power
-70
Ch3 Mix Pwr LO Start -25 dBm
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Freq 1.5 GHz
11
Stop 12 dBm
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Power Calibration
7. Power Calibration
Even though the power level accuracy of the ZVA sources and receivers are
quite good, we will in most cases need to perform a power level calibration.
Especially when we move into the GHz range, losses in cables and adapters
can be significant and influence the accuracy of our measurement. The power
calibration routine can even be configured to compensate for a pre-amplifier in
the signal path
To perform a power calibration, we need a Power Meter / Sensor connected to
the ZVA. The most convenient solution is using a USB Power Sensor from the
NRP-Z family such as the NRP-Z11 or NRP-Z51 sensor. Simply connect the
Power Sensor to the ZVA front panel USB connector and the sensor will be
automatically configured.
In case a normal Power Meter is used, press [SYSTEM CONFIG], then [System
Config] softkey and select the External Power Meters tab to configure the meter.
Please note that in case of using a normal Power Meter, you need the ZVABB44 option and the VISA I/O libraries installed on the ZVA. Even if a LAN
connection is used, you still need the VISA I/O libraries.
Please note that with this
hook active, just one NRP is
detected and controlled.
Click Refresh Tables to scan USB and GPIB interfaces for attached Power
Meters / Sensors. Select Power Meter to use in the Found: section and click
Add v to move it to the Configured: section.
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Power Calibration
Before starting the Calibration process, we need to consider the measurement
uncertainty contribution from the mismatch between the ZVA ports and the
mixer ports. On passive mixers we can expect typical Return Loss values in the
range from 10 to 20 dB. On the ZVA we have an uncorrected test port Return
Loss in the range from 10 to 16 dB, depending on frequency and ZVA model.
Using the standard mismatch error formula:
EM = 20 log10
1
dB
1± S L
We can see that a 12 dB Return Loss value for both ZVA and Mixer will give us
a mismatch uncertainty value of ~ +/-0.55 dB.
To reduce the mismatch uncertainty contribution in the mixer conversion loss
measurements, we can add fixed attenuators (often called matching pads)
between the ZVA and the mixer. This will improve the ZVA source match and
therefore reduce uncertainties. It is mainly on the RF and LO ports we have the
matching problems.
Improving the ZVA Return Loss with a matching pad to 30 dB, will reduce the
mismatch uncertainty value to ~ +/-0.07 dB.
The problem with matching pads is sometimes that we don’t have sufficient
power to drive the mixer. This is especially true for the LO signal, which typically
needs to be in the range from +7 to +15 dBm, depending on the mixer type.
Therefore extra amplification is sometimes required when using matching pads.
Please remember that the ZVA can deliver typically >15 dBm at the test port,
which often eliminate the need for an amplifier.
The optimal values for the matching pads are >=10 dB on order to provide good
isolation. We will however need to compromise due to the maximum power
available from the ZVA (~ +15 dBm).
In the following Power Calibration example we will use a 6 dB pad on the RF
port and a 3 dB pad on the LO port. No amplifier is used.
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Power Calibration
To start the power calibration process, do the following:
Select (Trc1) in channel 1. In this channel we are doing a frequency sweep.
Press [MODE], then [Scalar Mixer Meas] and [Scalar Mixer Meas Power Cal…]
softkeys. This will open the Scalar Mixer Measurement Power Calibration
window:
In the Source Cal Settings section we can see the values for the RF and LO
power levels for the active channel. Below that are two fields, this is the
Maximum Number of Readings (1) and Tolerance (1 dB) values. Those settings
determine the target accuracy for the power calibration and the maximum
number of iterations to obtain the specified accuracy. To change these settings,
press the Modify Settings… button.
Press Modify Cal Power to add Cal Power
Offset values in case external pads
and/or amplifiers are used.
Controls max number of iterations the
ZVA should use for reaching the
specified Tolerance value.
A good compromise between speed and accuracy in the power calibration could
be setting Maximum Number of Readings = 3 and Tolerance = 0.3 dB.
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Power Calibration
In case of using matching pads and/or external amplifiers in the setup, press the
Modify Cal Power button to add the proper offset. The example below shows the
compensation for a 6 dB matching pad at the ZVA port 1 (mixer’s RF port).
Please note the channel base power (Pb) initially must be set 6 dB higher to
compensate for the matching pad.
With the desired Source Cal Settings in place, the calibration process is started
by following the 3 steps in the left side of the Power Calibration window. 3 steps
are required to calibrate the 3 active ports on the ZVA. They are:
1.
2.
3.
RF Source Calibration
IF Receiver Calibration
LO Source Calibration
The calibration process can be monitored in the graphical plot and on the
progress bar below.
When step 3 is completed, press Close to close the Power Calibration window.
The power calibration of channel 1 is now completed.
Since the frequency and power settings of channel 2 and 3 are different from
channel 1, separate power calibrations on these channels must be performed as
well. The procedure is identical to the channel 1 calibration.
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Isolation Measurements
8. Isolation Measurements
The Isolation is a measure of signal leakage or feed-through from one mixer
port to another port. Good isolation corresponds to low leakage. Unbalance of
the internal transformers or lead inductance is the main cause of port-to-port
leakage. The amount of feed-through from the LO to the RF port is specified by
the LO-RF isolation. In an analogous way, the LO-IF isolation defines the level
at which the LO signal appears at the IF port.
Isolation is measured in dB and is a frequency-dependent quantity. High
isolation is preferable, since signal leakage will create spurious signal
components in the output spectrum.
9. Isolation Measurement Setup
The isolation measurement setup is identical to the conversion loss setup, here
shown for a 4-port ZVA only:
For measurement setup with a 2-port ZVA, please refer to section 3 for details.
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Arbitrary Port Configuration
10. Arbitrary Port Configuration
The configuration of isolation measurements is different from the conversion
loss setup. For these measurements, we cannot use the mixer configuration
wizard, we need to manually configure the ZVA source and receiver settings
using the [MODE], then [Port Config] keys to get to the Port Configuration menu.
The Port Configuration menu uses two terms named (fb) and (Pb):
(fb) is the base frequency entered using [START CENTER] and [STOP SPAN]
keys and (Pb) is the base power entered using the [PWR BW AVG] key.
In the above example, an external generator (Gen1) is configured, but not used.
So the error message shown can be ignored.
11. RF to IF Isolation Measurement
To start the RF to IF isolation measurement configuration, do the following:
Press [PRESET]
Press [START CENTER] and enter a start frequency of 1.3 GHz
Press [STOP SPAN] and enter a stop frequency of 1.6 GHz
Press [PWR BW AVG] and enter a power level of -10 dBm
Now the (fb) and (Pb) terms are set and we can start the actual configuration of
the test ports.
For this test we will again be using an IF frequency of 70 MHz and a LO signal
which is higher than the RF signal ( IF = LO – RF ).
Press [MODE], then [Port Config] keys to get to the Port Configuration menu.
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RF to IF Isolation Measurement
To configure the LO frequency and power, click on the (fb) and (Pb)
fields in the Port 3 row to open the Port 3 Source Frequency and Port 3
Cal Power configuration windows.
They allow you to configure the
frequency and power using (fb) and (Pb) as a base for the configuration,
or simply by typing in any desired value.
The LO frequency should be offset from the base freq (fb) by 70 MHz,
so we just add the 70 MHz in the configuration. For the LO power, we
want a fixed level of +7 dBm, which is configured as shown above.
Below is the completed RF to IF Isolation Configuration. Remember to
enable the generators for Port 1 and 3. Click OK to exit.
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RF to IF Isolation Measurement
Select the (b2/a1) as the quantity for RF to IF isolation measurement.
Please note that selecting S21 as the measurement quantity instead of
b2/a1, will allow for vector error correction (i.e. TOSM calibration) to be
applied to the measurement. This will further improve the measurement
accuracy, since vector error correction cannot be applied to the b2/a1
wave quantity measurement.
The result of the RF to IF Isolation measurement can be seen at the
green trace labeled RF2IF.
(Trc2) is the RF quantity in and (Trc3) is the RF quantity out (at IF port).
RF2IF b2/a1 dB Mag 10 dB / Ref 0 dB
Trc2 a1
dB Mag 10 dB / Ref 0 dBm
Trc3 b2
dB Mag 10 dB / Ref 0 dBm
PCal
PCal
PCal
1 of 4 (Max)
• M 1 1.450000 GHz -19.173 dB
b2/a1
10
b2/a1: RF
IF isolation
a1:
RF Power in
b2;
RF Power out
0
-10
M1
-20
-30
-40
-50
-60
-70
Ch1 Arb Channel Base Start 1.3 GHz Pwr -10 dBm
Stop 1.6 GHz
HINT: Use the mouse and Right-Click on the trace name to access the Trace
Manager. Here you can change the name of the trace to something more
meaningful than Trc1, Trc2, etc.
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LO to IF Isolation Measurement
12. LO to IF Isolation Measurement
To start the configuration:
Press [CHAN SELECT], then [Add Channel + Trace + Diag Area] softkey. This
will create a second channel in a new diagram area, which is identical to the first
channel.
Select the (b2/a3) as the quantity for LO to IF isolation measurement (or
select S23 to allow for vector error correction).
Press [MODE], then [Port Config] keys to get to the Port Configuration menu.
The main difference from the previous measurement is that we want to measure
the amount of LO signal at the IF port. All the Source settings are therefore the
same as before, but the receiver must be re-configured to measure the LO
instead if the RF signal.
To do this, click on the Frequency field in the receiver section of the Port
Configuration menu. Then add the 70 MHz offset so that the configuration result
is identical to what is shown above.
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LO to IF Isolation Measurement
The result of the LO to IF Isolation measurement can be seen at the red
trace labeled LO2IF.
b2/a3: LO
IF isolation
a3:
LO Power in
b2;
LO Power out
(Trc6) is the LO quantity and (Trc5) is also the LO quantity, but
measured at the IF port.
LO2IF b2/a3 dB Mag 10 dB / Ref 0 dB
Trc5 b2
dB Mag 10 dB / Ref 0 dBm
Trc6 a3
dB Mag 10 dB / Ref 0 dBm
PCal
PCal
PCal
2 of 4 (Max)
• M 1 1.450000 GHz -16.716 dB
b2/a3
10
0
-10
M1
-20
-30
-40
-50
-60
-70
Ch2 Arb Channel Base Start 1.3 GHz Pwr -10 dBm
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Stop 1.6 GHz
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LO to RF Isolation Measurement
13. LO to RF Isolation Measurement
To start the configuration:
Press [CHAN SELECT], then [Add Channel + Trace + Diag Area] softkey. This
will create a third channel in a new diagram area, which is identical to the
second channel.
The port configuration for LO to RF isolation is identical to the previous
one, so we just need to select the (b1/a3) as the measurement quantity
for the LO to RF isolation measurement.
(Or as with the previous isolation measurements, select S13 to allow for
vector error correction)
The result of the LO to RF Isolation measurement can be seen at the
light green trace labeled LO2RF.
(Trc8) is the LO quantity and (Trc9) is also the LO quantity, but
measured at the RF port.
b1/a3: RF
IF isolation
a3:
LO Power in
b1;
LO Power out
LO2RF b1/a3 dB Mag 10 dB / Ref 0 dB
Trc8
a3
dB Mag 10 dB / Ref 0 dBm
Trc9
b1
dB Mag 10 dB / Ref 0 dBm
3 of 4 (Max)
• M 1 1.450000 GHz -34.436 dB
b1/a3
10
0
-10
-20
M1
-30
-40
-50
-60
-70
Ch3 Arb Channel Base Start 1.3 GHz Pwr -10 dBm
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Stop 1.6 GHz
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Power Calibration for Isolation Measurement
14. Power Calibration for Isolation Measurement
Unlike in the Mixer wizard for the conversion loss measurements, which also
included an intuitive procedure for the power calibration, we need to go through
a less automated procedure for the Isolation Measurement Calibration. In other
words, we need to make sure that we cover all frequency ranges of interest for
both sources and the receiver during our calibration.
In this section we will go through a calibration example for the RF to IF Isolation
measurement. See section 11 for details.
In this RF to IF Isolation measurement, we are measuring the RF frequency
range from 1.3 GHz to 1.6 GHz with an IF frequency of 70 MHz. Subsequently
this will give us an LO frequency range from 1.37 GHz to 1.67 GHz when using
IF = LO – RF in the frequency conversion.
With the connections to the mixer as shown below (left), we can make a graph
of the frequency ranges for each port on the ZVA (right) that requires a power
calibration.
The two sources needs to be calibrated over their respective frequency ranges
and the receiver needs to be calibrated, NOT at the IF frequency, but at the RF
frequency range. From the plot above we can see that it makes sense to use
the port 1 source for calibration of the port 3 receiver.
The 3 calibration measurements required are as follows:
1.
2.
3.
Port 1 source calibration using a Power Meter / Sensor.
Port 3 source calibration using a Power Meter / Sensor.
Port 2 receiver calibration using the calibrated port 1 as the source.
In step 3 we are using the calibrated port 1 as a “transfer standard” from the
Power Sensor to the port 2 receiver. The accuracy of the port 2 receiver
calibration will be slightly worse than the port 1 source calibration.
The power calibrations should be performed in the order shown above.
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Power Calibration for Isolation Measurement
To start the source Power Calibration process:
Press [CAL], then [Start Power Cal ] and [Source Power Cal…] softkeys to
open the Source Power Cal dialog window.
Configuration of a Power
Meter/Sensor and optionally
zeroing of the Sensor
First step is selecting which port to calibrate using the Source “Drop-down”
menu. Select Port 1. Connect the configured Power Sensor to the port 1 cable.
If a Power Meter is not configured, click on the Power Meter Config button to
access the Power Meter configuration menu. See section 7 for more information
on configuring a Power Meter.
Click on Modify Settings… button to access Modify Source Power Cal Settings
dialog window. Adjust settings as required. Click OK button when done.
Press Modify Cal Power to add Cal Power
Offset values in case external matching
pads and/or amplifiers are used.
Controls max number of iterations the
ZVA should use for reaching the
specified Tolerance value.
Check this box if more than one source
shares the same calibration point.
(Required when two sources are feeding
a combiner and they are calibrated at
the combiner output)
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Power Calibration for Isolation Measurement
Click on Take Cal Sweep and the power calibration will start with the settings
configured. The calibration progress can monitored in the graphical display.
When completed, Pass (or fail) is indicated in the lower left corner together with
the maximum deviation value. Click Close to End port 1 calibration.
Repeat the calibration process for port 3 following the same procedure.
To start the receiver Power Calibration process:
Press [CAL], then [Start Power Cal
] and [Receiver Power Cal…]
softkeys to open the Receiver Power Cal dialog window.
Select the Wave Quantity to Calibrate, in our case it is the b2 quantity.
Select the Used Source, in our case it is port 1 we want to use.
Connect the calibrated port 1 cable to the port 2 cable.
Click the Take Cal Sweep button, wait a few seconds until the calibration
completes. You can monitor the Sweep progress bar.
Click Close to complete the receiver power calibration.
This completes the Source power calibration process for the two sources at port
1 and 3 and the Receiver power calibration process at port 2.
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RF and LO Port Return Loss Measurement
15. RF and LO Port Return Loss Measurement
With traditional two-port Network Analyzers, S-parameter measurements like
the S11 on the RF port had to be carried out using an external Signal Generator
supplying the LO signal to the mixer. Since there was no frequency control of
the generator, a fixed LO frequency was typically used while sweeping the RF
frequency range of interest.
With the ZVA, it is now possible to measure the port matching parameters while
the mixer is operating under realistic conditions. That is measuring the S11 of
the RF port while the LO port is being feed with both the correct frequency and
amplitude. Or measuring the S33 of the LO port with a proper RF signal applied.
Again we will need to use the Port Configuration menu to setup the proper
conditions for the mixer, before making the S-parameter measurements.
In this example we will again be measuring the 1.3 to 1.6 GHz frequency range
with an IF frequency of 70 MHz.
To start the configuration:
Preset the ZVA, then setup start/stop frequencies and a power level of -10 dBm.
Select S11 as the measurement quantity for RF port Return Loss.
Press [MODE], then [Port Config] keys to get to the Port Configuration menu
and make the configuration shown below:
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RF and LO Port Return Loss Measurement
To add a S33 measurement (LO) to the configuration:
Press [CHAN SELECT], then [Add Channel + Trace] softkey. This will create a
second channel in the same diagram area, which is identical to the first channel.
Select S33 as the measurement quantity for LO port Return Loss.
Press [MODE], then [Port Config] keys to get to the Port Configuration menu.
Change the Receiver Frequency setting, so that it is the LO frequency that is
being measured.
The result of the S11 and S33 measurements can be seen below.
RF_vswr S11 dB Mag 10 dB / Ref 0 dB Ch4 Cal
LO_vswr S33 dB Mag 10 dB / Ref 0 dB Ch5 Cal
4 of 4 (Max)
• M 1 1.450000 GHz -9.0793 dB
M 1 1.450000 GHz -13.542 dB
S11
10
0
HINT: The S11 and S33 plots are
shown in Return Loss format. Use
[FORMAT] and [SWR] or [Lin Mag]
softkeys to display the reflection
measurements in VSWR or Reflection
Coefficient formats respectively.
M1
M1
-10
-20
-30
[dB Mag] returns the reading to the
Return Loss format.
-40
-50
-60
-70
Ch4 Arb Channel Base Start 1.3 GHz Pwr -10 dBm
Ch5 Arb Channel Base Start 1.3 GHz Pwr -10 dBm
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Stop 1.6 GHz
Stop 1.6 GHz
Rohde & Schwarz
RF and LO Port Return Loss Measurement
To ensure the best accuracy possible in the mixer S-parameter measurements,
the following calibrations should be made:
•
S11 One-port calibration
•
S33 One-port calibration
•
Port 1 Power Calibration
•
Port 3 Power Calibration
The screenshots below summarizes the Isolation and the Reflection measurements, configured in the previous sections.
RF_IF b2/a1 dB Mag 10 dB / Ref 0 dB
Trc2 a1
dB Mag 10 dB / Ref 0 dBm
Trc3 b2
dB Mag 10 dB / Ref 0 dBm
b2/a1
10
0
-10
-20
-30
-40
-50
-60
-70
PCal
PCal
PCal
1
•M1 1.450000 GHz -18.794 dB
M1
RF to IF isolation
Ch1 Arb Channel BasePwr
Start
-101.3
dBm
GHz
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3
M1 1.450000 GHz -35.801 dB
M1
LO to RF isolation
Ch3 Arb Channel BasePwr
Start
-101.3
dBm
GHz
b2/a3
10
0
-10
-20
-30
-40
-50
-60
-70
LO to IF isolation
Stop 1.6 GHz
RF_vswr S11 dB Mag 10 dB / Ref 0 dB Ch4 Cal
LO_vswr S33 dB Mag 10 dB / Ref 0 dB Ch5 Cal
S11
10
0
-10
-20
-30
-40
-50
-60
-70
2
M1
4
M1 1.450000 GHz -9.0446 dB
M1 1.450000 GHz -13.567 dB
M1
M1
RF and LO Port Match
Ch4 Arb Channel BasePwr
Start
-101.3
dBm
GHz
Stop 1.6 GHz Ch5 Arb Channel BasePwr
Start
-101.3
dBm
GHz
28
PCal
PCal
PCal
M1 1.450000 GHz -16.902 dB
Stop 1.6 GHz Ch2 Arb Channel BasePwr
Start
-101.3
dBm
GHz
LO_RF b1/a3 dB Mag 10 dB / Ref 0 dB
Trc8
a3
dB Mag 10 dB / Ref 0 dBm
Trc9
b1
dB Mag 10 dB / Ref 0 dBm
b1/a3
10
0
-10
-20
-30
-40
-50
-60
-70
LO_IF b2/a3 dB Mag 10 dB / Ref 0 dB
Trc5 b2
dB Mag 10 dB / Ref 0 dBm
Trc6 a3
dB Mag 10 dB / Ref 0 dBm
Stop 1.6 GHz
Stop 1.6 GHz
Rohde & Schwarz
Intermodulation Measurement
16. Intermodulation Measurement
The multiport / multisource concept of the ZVA and the ability to control external
Signal Generators allows us to take mixer measurements even further and
measure parameters like the Third Order Intermodulation (or IP3) product. For
this, a 4-port ZVA and an external Signal Generator is required.
Please note that if a 6 port (3 generators) or 8 port ZVT (4 generators) is
available, no external Signal Generator is required. The ZVT can then provide
all the signals required.
Furthermore, a passive combiner is required to combine the two RF signals
before applying them to the mixer. The signal generator will provide the LO
signal to the mixer, as shown in the setup below. Low pass filters for reducing
harmonic products from the sources are optional, but sometimes required.
We will in our example here again measure the mixer in the RF frequency range
from 1.3 GHz to 1.6 GHz with an IF frequency of 70 MHz. We will use an LO
which is higher than the RF (IF = LO – RF), so the LO frequency range is 1.37
GHz to 1.67 GHz.
Pin
f1
f2
f
The ZVA will provide the two signals required for the IP3 measurement. A
default spacing of 1 MHz will be used.
f1 will sweep from 1.300 GHz to 1.600 GHz and f2 will sweep from 1.301 GHz to
1.601 GHz.
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Intermodulation Measurement
Due to the mixer conversion, new carriers are created as follows:
C1 = LO – F1
example : 1370 MHz – 1300 MHz = 70 MHz
C2 = LO – F2
example : 1370 MHz – 1301 MHz = 69 MHz
And the IP3 products created are as follows:
IP3+ = 2*C1 – C2
example : 2*70 MHz – 69 MHz
= 71 MHz
IP3- = 2*C2 – C1
example : 2*69 MHz – 70 MHz
= 68 MHz
The Third Order Intercept (TOI) point can be calculated as follows:
TOI Point Calculation
Pout
IP dBc
IP dBc
TOI = Pout + ----------2
In our example, we will use C1 (70 MHz) and IP3+ (71 MHz) when we configure
the IP3 measurement on the ZVA. First we will configure a classic Spectrum
Analyzer view, measuring at a single frequency. Then we will configure a swept
IP3 measurement
To start the IP3 measurement configuration, connect the hardware as shown on
the previous page, then do the following:
Press [PRESET]
Press [START CENTER] and enter a start frequency of 65 MHz
Press [STOP SPAN] and enter a stop frequency of 75 MHz
Press [PWR BW AVG] and enter a power level of 0 dBm
Press [PWR BW AVG], then [Meas Bandwidth] and [Fine Adjust] softkeys.
Enter 50 kHz bandwidth and select High Selectivity.
Please note that the measurement bandwidth selected must be smaller than the
frequency spacing of the two tones. This is required in order for the ZVA to be
able to distinguish between them in the receiver.
Now the (fb), (Pb) terms and the bandwidth are set and we can start the actual
configuration of the test ports.
Press [MODE], then [Port Config] keys to get to the Port Configuration menu.
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Intermodulation Measurement
Configure the generators at port 1 and 3 to produce a CW (non-sweeping)
signal with 1 MHz spacing. Configure the external generator to produce a CW
signal of 1.57 GHz for the LO port. Set the LO power to +8 dBm.
See chapter 11 (page 18)
for details on frequency
and power configuration
menus.
Select the (b2) as the measurement quantity.
The result of the non-sweeping IP3 measurement can be seen at the
graphical plot below. The main products we are looking for are marked
with red circles. The other signals shown in the measurement plot are
spurs caused by mixing with the LO signal.
SA_view b2 dB Mag 10 dB / Ref 0 dBm
1 of 2 (Max)
M 1 70.000000 MHz -9.4486 dBm
• M 2 71.000000 MHz -36.994 dBm
b2
10
0
M1
-10
-20
-30
M2
-40
-50
-60
-70
Ch1 Arb Channel Base Start 65 MHz
Pwr 0 dBm
Stop 75 MHz
The benefit of starting with this measurement setup is that it gives us a good
overview of the configuration made. Do we have a good S/N ratio in the
measurement? Are the ZVA source levels appropriate for the measurement? If
not, then it can be adjusted using this view before we start the swept IP3
measurement.
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Intermodulation Measurement
In the swept IP3 measurement we will focus on the C1 (70 MHz) and IP3+ (71
MHz) products. To start the configuration of the swept IP3 measurement:
Press [CHAN SELECT], then [Add Channel + Trace + Diag Area] softkey. This
will create a second channel in a new diagram area.
Select the (b2) as the measurement quantity.
Press [MODE], then [Port Config] keys to get to the Port Configuration menu.
Make the configuration shown below. Please note that the ZVA sources and the
external generators are now sweeping and that the ZVA receiver is fixed at the
C1 frequency (70 MHz).
Press [CHAN SELECT], then [Add Channel + Trace] softkey. This will create a
third channel in the same diagram area.
Select the (b2) as the measurement quantity.
Press [MODE], then [Port Config] keys to get to the Port Configuration menu.
Make the configuration shown below. Please note that the only change required
is setting the ZVA receiver for the IP3+ frequency (71 MHz).
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Intermodulation Measurement
We now have the 2 traces for measuring the C1 and IP3+ frequencies defined.
rd
Since the 3 Order Intercept point is a calculated value, we need to create a
trace that takes the data from the C1 and IP3+ traces and calculate the values.
The ZVA offers the possibility to display traces based on calculated values,
rather than measured values. The data used for these calculations can be data
from other traces, mathematical operators, constants, etc.
Press [CHAN SELECT], then [Add Channel + Trace] softkey. This will create a
fourth channel in the same diagram area.
Press [TRACE FUNCT], then [User Def Math] keys to get to the User Def Math
menu. Use the Operand and Operator fields to create the highlighted equation.
Please note that the equation editor does its calculations in linear format, so we
need to convert the measured trace data before we can used them.
Set a checkmark in Results is Wave Quantity and press OK.
Press [TRACE FUNCT], then [Math = User Def] keys to enable use of the user
defined math trace.
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Rohde & Schwarz
Intermodulation Measurement
Trc2: C1 quantity
Trc3: IP3+ quantity
OIP3 : TOI intercept
The calculated result of the swept IP3 measurement can be seen at the
red trace labeled OIP3.
(Trc2) is the C1 quantity and (Trc3) is the IP3+ quantity, measured at
the mixers IF port.
Trc2 b2 dB Mag 10 dB / Ref 0 dBm Ch2
Trc3 b2 dB Mag 10 dB / Ref 0 dBm Ch3
OIP3 b2 dB Mag 10 dB / Ref 0 dBm Ch4 Math
2 of 2 (Max)
• M 1 1.450000 GHz 4.8231 dBm
b2
M1
10
0
-10
-20
-30
-40
-50
-60
-70
Ch2 Arb Channel Base Start 1.3 GHz Pwr 0 dBm
Ch3 Arb Channel Base Start 1.3 GHz Pwr 0 dBm
Ch4 Arb Channel Base Start 1.3 GHz Pwr 0 dBm
Stop 1.6 GHz
Stop 1.6 GHz
Stop 1.6 GHz
Again, In order to ensure the best accuracy possible, power calibrations must be
performed on both ZVA sources (port 1 and 3) and the external generator. Also
the ZVA receiver on port 2 should be calibrated.
Calibration point for the ZVA sources should be at the power combiner Output.
Make sure that other sources are switched off during calibration of the individual
sources.
Refer to section 14 for more information on power calibration.
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Rohde & Schwarz
Additional Information
17. 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 [email protected]
18. Ordering Information
Listed are all R&S ZVA/T network analyzers and most important
options. Of course, accessories like test cables, or manual and
automatic calibration kits are available in addition. There is also a wide
variety of R&S NRP test heads for power measurement and power
calibration. 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
1164.1657.02
R&S ZVA-K2
Time Domain (TDR)
1164.1863.02
R&S ZVA-K4
Frequency Conversion
1164.1540.02
R&S ZVA-K6
True Differential Measurements
1164.1511.02
R&S ZVA-K7
Pulsed Measurements
1302.5544.02
R&S ZVAB-B44
USB-to-IEC/GPIB Adapter
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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Rohde & Schwarz
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