1EZ50_0E
Products: ZVRE, ZVR, ZVCE, ZVC, ZVM, ZVK
Conversion Gain Measurements on Mixers
with Different
Input and Output Impedances
This Application Note describes how to configure and calibrate R&S ZVR network analyzers for conversion
gain measurements of devices with two ports that have different impedances. Thus accurate
measurements on frequency-converting devices such as low noise converters of sattellite receivers are
possible.
Subject to change – Thilo Bednorz 05. 02– 1EZ50_0E
Mixer Measurements
Contents
1 Overview.................................................................................................. 2
2 ZVR Principles of Operation for Measurements on Mixers .................... 2
3 RZVR Calibration for Measurements on Mixers...................................... 4
Power Calibration of the Generator ...................................................5
Power Calibration of the Receiver .....................................................6
4 Example................................................................................................... 8
Configuring the Segmented Sweep....................................................9
Calibrating the Generator and Receiver ...........................................10
Measurement ...................................................................................10
5 Appendix................................................................................................ 13
6 Further Application Notes ...................................................................... 14
7 Additional Information............................................................................ 15
8 Ordering Information.............................................................................. 15
1 Overview
This Application Note describes how to configure and calibrate R&S ZVR
network analyzers to perform conversion gain measurements on devices
with two ports that have different impedances. Accurate measurements can
now be made on frequency-converting devices with different input and
output impedances, such as converters of satellite receicers.
2 Principles of Operation for Measurements on a FrequencyConverting Device
.
Ideal mixers are perfect multipliers that multiply the radio frequency (RF)
input signal by a local oscillator (LO) signal. This produces the so called
intermediate frequency (IF) signals at the mixer output.
IF = RF + LO and
IF = RF − LO
Mixer conversion loss is defined to be the ratio of the complex RF input
power Pin at frequency f1 and the IF output power Pout at frequency f2.
Conversion loss =
1EZ50_0E
Pin
Pout
2
Rohde & Schwarz
Mixer Measurements
RF
f1
f2
IF
LO
Fig. 2-1
Definition of the input and output signals of the mixer
Since the input and output frequencies of a mixer usually differ, it is not
possible to determine the ratio of the input signal and the output signal by
magnitude and phase, which would also be necessary for complete systemerror correction. Instead, the magnitude of the RF input power and the
magnitude of the IF output power at f1 and f2 respectively are determined
to calculate a scalar ratio. If the mixer has different input and output
impedances, one or both measurement ports must be fitted and calibrated
with appropriate matching pads.
For measurements on frequency-converting devices with instruments of the
R&S ZVR family, the generator is set to the RF input frequency f1, and all
receivers to the converter’s IF output frequency f2. Since all receivers use a
common LO signal, the reference receiver a1 cannot be used to measure
the mixer’s RF input power, a1, as it is the case with S-parameter
measurements. Instead, the generator power is measured with the
broadband level detector which is also used to control the generator output
level (Fig. 2-2). The scalar power Pa1, determined by the detector, is,
therefore, equal to the generator output level set in the network analyzer’s
source menu, this is why the conversion gain in the MEAS menu of the R&S
ZVR is also designated b2/Pa1.
level detector
reference receiver a1
b1
Pa1
local oscillator
a1
generator
a2
Pa2
measurement receiver b2
b2
ZVR
Pin
Pout
f1
a1
f2
b2
DUT
Fig. 2-2
1EZ50_0E
Simplified block
measurements
3
diagram
of
a
ZVR
setup
for
mixer
Rohde & Schwarz
Mixer Measurements
3 ZVR Calibration for Measurements on Mixers
The accuracy of measurements on frequency-converting devices is
determined primarily by the frequency response of the test setup, the
linearity of the level detector and the matching of the measurement ports. At
high frequencies in particular, the measurement error can be several dB.
Errors due to the non-linearities of the selective measurement receiver b2
are usually negligible (see Appendix Fig. 5-1).
To improve the matching of the measurement ports, screw well-matched
attenuators directly on to the ends of the measurement cables. If a highquality, well-matched matching pad (e.g. R&S RAM) is used for impedance
transformation at one of the measurement ports, only the 50 Ω port needs
to be equipped with a well-matched attenuator. The additional loss caused
by the attenuators and matching pads will of course influence the
conversion gain measurement. A power calibration of the generator and the
receiver makes it possible to determine and largely eliminate the influence
of the complete test setup, and so also the losses caused by the
attenuators and matching pads.
The Power Calibration Option R&S ZVR-B7 as well as the power meter and
power sensor supported by this option are required to perform this power
calibration. Because they are faster, diode sensors are preferred to thermal
power sensors.
Instruments from the ZVR family support the following power meters for
power calibration:
• R&S NRV
• R&S NRVS
• R&S NRVD
• Agilent HP 437
• Agilent HP 438
• Agillent E4417A
• Anritsu ML 2438A
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Mixer Measurements
Generator Power Calibration
IEC/IEEE bus
ROHDE & SCHWARZ VECTOR
NETWORK ANALYZER ⋅ 10 Hz ... 4 GHz ⋅
1127.8500.60
ZVR
NRVS
Fig. 3-1 Generator calibration using a power meter
To calibrate the generator, the power sensor is connected to the generator
port in the measurement plane. The power meter is connected to the R&S
ZVR via the IEEE system bus. For every frequency point, an automatic
iteration process determines suitable correction values for the level detector
of the analyzer’s generator to set the required nominal level in the reference
plane. If the generator power level is changed between calibration and
measurement, accuracy depends on the linearity of the level detector Pa1
(see Appendix Fig 5-1).
Receiver Power Calibration
Fig. 3-2
Receiver calibration using the power-calibrated generator
The ZVR’s power-calibrated generator is now a high-precision source to
calibrate the R&S ZVR receiver b2 that has to be connected to the receiver
in the measurement plane. The generator and receiver simultaneously
sweep the same frequencies. At every frequency point, the ZVR compares
the power measured by the b2 receiver to the power applied by the
calibrated generator and determines receiver correction data from this
difference. The absolute power measurement accuracy of the receiver (with
an ideally matched and calibrated generator) mainly depends on the return
loss of the DUT and the test port match. Receiver linearity errors are
basically negligible over a wide level range.
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Mixer Measurements
Power calibration for Measurements on FrequencyConverting Devices
The power calibration for conversion gain measurements on mixers or
converters requires several steps.
Power calibration for Mixers/Converters with the Same Input and
Output Impedances
1. Calibrate the generator (strictly speaking the level detector) with the power
meter at the RF input frequency and at the IF output frequency. The latter is
necessary because the generator calibrated for the IF is also used to
calibrate the receiver that is measuring the IF output signal. The frequency
range to be calibrated, therefore, encompasses the whole RF and IF range.
2. Calibrate the receiver using the previously calibrated generator. The
generator port and receiver port are connected back-to-back. The receiver is
calibrated over the whole RF and IF frequency range as well.
Power calibration for Mixers/Converters with Different Input and
Output Impedances
If impedances of both ports of the DUT are different, e.g. a 50 Ω input and a
75 Ω output)
1. Calibrate the generator and the receiver for the mixer output impedance. If,
for example, the DUT has a 50 Ω input and a 75 Ω output, terminate the
network analyzer’s measurement ports with 75 Ω matching pads and
calibrate the complete setup in a 75 Ω environment.
2. Remove the matching pad from the generator port and recalibrate the
generator for the input impedance by using a 50 Ω power sensor connected
to the generator port.
Two rules must be observed to achieve maximum measurement accuracy:
•
Use well-matched matching pads and attenuators
The power calibration only eliminates the frequency response of the
test setup, but not measurement errors due to test port mismatch.
Make certain to use well-matched matching pads and attenuators
directly in the measurement plane. If the same test setup is used to
determine not only the conversion gain, but also the reflection
coefficient of the converter, the attenuation at the appropriate port may
not exceed 10 dB.
•
Use the segmented sweep for power calibration
Since the power calibration must cover the RF and IF frequency ranges, a
lot of test points between RF and IF would be “wasted“ in a linear frequency
sweep, especially in microwave applications. The spacing of the calibrated
test points in the subsequently measured RF and IF bands would therefore
be large. If a frequency is converted, from 38 GHz to 100 MHz for example,
the frequency spacing is almost 19 MHz even if the maximum number of
measurement points (2001) is used during calibration. The interpolation of
correction values for subsequent test points may cause large measurement
errors.
To avoid this problem, the instruments of the ZVR family (firmware 3.40 or
higher) supports a power calibration using a segmented sweep. Up to 40
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Rohde & Schwarz
Mixer Measurements
different frequency segments can be defined in this sweep mode, and their
points can be distributed almost arbitrarily along the frequency axis. Exactly
those points that are subsequently used for measurements can be calibrated
if two segments are selected, one for the RF input frequency and one for
the IF output frequency, each with the same span and the same number of
test points. Interpolation errors are, therefore, ruled out.
¦
SEGM START
1
1000 MHz
2
11 GHz
STOP
2 GHz
12 GHz
SWEEP SEGMENTS
POINTS SRC PWR
201
-20 dBm
201
-20 dBm
TIME
AUTO
AUTO
AVG
1
1
IF BW LO1
10 kHz +
10 kHz +
For further details on power calibration, see Application Note 1EZ41_2,
Power Calibration of Vector Network Analyzer ZVR.
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Mixer Measurements
4 Example
A converter with a constant LO (10 GHz) converts an RF signal with a
frequency between 11 GHz to 12 GHz to an IF between 1 GHz and 2 GHz.
The RF input impedance is 50 Ω, the IF output impedance 75 Ω.
RF
11 GHz to 12 GHz
LO (internal)
10 GHz
IF
1 GHz to 2 GHz;
11 GHz to 12 GHz
50 Ω
Pin
Pout
f(IF) = f(RF)-f(LO)
1 GHz to 2 GHz
75 Ω
L
O
Fig. 4-2
Frequency converter with different input and output impedances
The following accessories are used for calibration and measurement:
1EZ50_0E
Vector Network Analyzer
R&S ZVM
Power Calibration Option
R&S ZVR-B7
Mixer Measurements Option
R&S ZVR-B4
Matching Pads (50 Ω / 75 Ω)
R&S RAM (2x)
Attenuator
R&S DNF 6 dB
Power Meter
R&S NRVD
Power Sensor 50 Ω
R&S NRV-Z1
Power Sensor 75 Ω
R&S NRV-Z3
8
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Mixer Measurements
Configuring Segmented Sweeps
To prevent errors due to correction-data interpolation, use the segmented
sweep for calibration. The first segment covers the frequency range of the
IF output signal (1 GHz to 2 GHz), the second segment the RF input signal
(10 GHz to 11 GHz). The frequency span and the number of test points for
both segments are identical. The number of test points per segment must
be identical to the number of test points for the subsequent measurement.
This ensures that the test point grid for calibration and for measurement is
exactly the same.
PRESET:
SWEEP:
DEFINE SWEEP SEGMENTS
INSERT NEW SEGMENT
INSERT NEW SEGMENT
ã
SWEEP SEGMENTS
LO1
TIME
AVG
IF BW
1
1000 MHz
2 GHz
201
-20 dBm
AUTO
1
10 kHz
+
2
11 GHz
12 GHz
201
-20 dBm
AUTO
1
10 kHz
+
SEGM START
STOP
POINTS SRC PWR
Ö
SEG SWEEP
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Rohde & Schwarz
Mixer Measurements
Calibrating the Generator and Receiver
1. In the measurement plane, screw 75 Ω matching pads to both ends of
the measurement cable to perform the power calibration for the DUT
output impedance (75 Ω).
2. Connect the power meter’s IEEE bus to the IEC/IEEE system bus of the
R&S ZVR (IEC/IEEE system bus).
3. Set the instrument-specific data of the power meter in the R&S ZVR’s
configuration menu.
4. Connect the 75 Ω sensor to the measurement plane (directly in front of
the DUT input)
5. Calibrate the generator.
CAL:
START NEW POWER CAL
POWER METER CONFIG
ã
POWER METER CONFIG
TYPE
GPIB ADDR AUTO ZERO SENSOR CAL FACTOR
NRVS
17
/
DATA FROM SENSOR
NUMBER OF READINGS 1
CAL a1 –20 dBm
TAKE CAL SWEEP
6. Connect the calibrated generator directly to the receiver via a wellmatched, low-loss adapter (THROUGH from a 75 Ω calibration kit) to
calibrate the receiver.
CAL b2 POWER
TAKE CAL SWEEP
The generator and receiver (both 75 Ω) are now calibrated. The CAL a1
and CAL b2 enhancement labels are active.
7. Calibrate the generator for 50 Ω. The matching pad is removed and
replaced with a well-matched attenuator. The 50 Ω sensor and port 1
are connected and the generator is then calibrated again. It is
absolutely essential to use the output level you are going to use for
subsequent measurements for the calibration too.
CAL:
CAL a1
-20 dBm
TAKE CAL SWEEP
After the test system has been calibrated, connect the converter. The
generator and receiver settings for conversion gain measurements are
configured in mixer mode.
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Rohde & Schwarz
Mixer Measurements
Measurement
ROHDE & SCHWARZ VECTOR
NETWORK ANALYZER ⋅ 10 Hz ... 4 GHz ⋅
ZVR
1127.8500.60
ZVR
Matching Pad
RAM
Attenuator DNF
6 dB
50 Ω
75 Ω
DUT
Fig. 4-3
Test setup
SWEEP
LIN SWEEP
MODE
FREQUENCY CONVERS
DEFINE MIXER MEAS
IF=BASE FREQUENCY
START 1 GHz
STOP 2 GHz
FIXED LO 10 GHz
SEL BAND (+)
Ö (to return to the higher-level softkey menu and switch
off the configuration graphics)
MIXER MEAS (activates the mixer measurement mode
and automatically selects b2/Pa1)
The configuration-graphics display clearly shows the R&S ZVR settings.
When you press Ö, the graphics cease to be displayed, but they can be
recalled whenever you want by pressing DEFINE MIXER MEAS.
MIXER FREQUENCIES
RF-
RF+
LO
IF
t
0
f
RF- = |LO-IF|
PORT1
PORT2
RF
INT. SOURCE
11 GHz .. 12 GHz
RF+ = LO+IF
IF
LO
RECEIVER
1 GHz .. 2 GHz
EXT. SOURCE
10 GHz
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Mixer Measurements
The measured conversion gain is displayed on the screen.
CH1 b2/Pa1
dB
MAG ↓ -50 dB
↑ 30 dB
1:
13.16 dB
1.9 1.4
GHz GHz
30 dB
1
MIX
ADD
PCI
a1
10 dB/
b2
CPL
FIL
1k
-50 dB
START
1 GHz
Fig. 4-4
100 MHz/
STOP 2 GHz
Measured conversion gain of a converter
Because the frequency range and number of test points were different for
calibration and measurement, the Power Calibration Interpolated (PCI)
enhancement label shows that the test-point correction values are
interpolated. This is not the case, of course – the algorithm is simply not
smart enough to handle the situation.
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Mixer Measurements
5 Appendix
Fig. 5-1
Typical linearity of the receiver b2 at 50 MHz
CH1 a1
dB
MAG ↓-30 dBm
↑15 dBm
1:
-25.14 dBm
2:
-25
dBm
-2
dBm
-18.06 dBm
3:
-10.00 dBm
4:
-5.002 dBm
5:
0.035 dBm
15 dBm
-18 dBm
-10 dBm
-5 dBm
0 dBm 5
ADD
4
5 dB/
3
CPL
2
FIL
1k
1
CW 1 GHz
-30 dBm
START
-25 dBm
Date:
Fig. 5-2
1EZ50_0E
10.OCT.01
2 dB/
STOP 0 dBm
08:17:26
Typical output-level linearity at 1 GHz
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Rohde & Schwarz
Mixer Measurements
6 Further Application Notes
[1]
O. Ostwald: 3-Port Measurements with Vector Network Analyzer ZVR, Appl.
Note 1EZ26_1E, 26 July 1996.
[2]
H.-G. Krekels: Automatic Calibration of Vector Network Analyzer ZVR, Appl.
Note 1EZ30_2E, 30 August 1996.
[3]
O. Ostwald: 4-Port Measurements with Vector Network Analyzer ZVR, Appl.
Note 1EZ25_1E, 10 October 1996.
[4]
T. Bednorz: Measurement Uncertainties for Vector Network Analysis, Appl.
Note 1EZ29_1E, 21 October 1996.
[5]
P. Kraus: Measurements on Frequency-Converting DUTs using Vector
Network Analyzer ZVR, Appl. Note 1EZ31_1E, 5 November 1996.
[6]
J. Ganzert: File Transfer between Analyzers FSE or ZVR and PC using MSDOS Interlink, Appl. Note 1EZ34_1E, 25 April 1997.
[7]
J. Ganzert: Accessing Measurement Data and Controlling the Vector
Network Analyzer via DDE, Appl. Note 1EZ33_1E, 28 April 1997.
[8]
O. Ostwald: Group and Phase Delay Measurements with Vector Network
Analyzer ZVR, Appl. Note 1EZ35_1E, 10 July 1997.
[9]
O. Ostwald: Multiport Measurements using Vector Network Analyzer, Appl.
Note 1EZ37_2E, 10 October 1997.
[10] O. Ostwald: Frequently Asked Questions about Vector Network Analyzer
ZVR, Appl. Note 1EZ38_3E, 19 January 1998.
[11] A. Gleißner: Internal Data Transfer between Windows 3.1 / Excel and
Vector Network Analyzer ZVR, Appl. Note 1EZ39_1E, 22 January 1998.
[12] A. Gleißner: Power Calibration of Vector Network Analyzer ZVR, Appl. Note
1EZ41_2E, 10 March 1998.
[13] O. Ostwald: Pulsed Measurements on GSM Amplifier SMD ICs with Vector
Network Analyzer ZVR, Appl. Note 1EZ42_1E, 19 May 1998.
[14] O. Ostwald: Time Domain Measurements using Vector Network Analyzer
ZVR, Appl. Note 1EZ44_0E, 19 May 1998.
[15] O. Ostwald: T-Check Accuracy Test for Vector Network Analyzers utilizing a
Tee-junction, Appl. Note 1EZ43_0E, 3 June 1998.
[16]
J. Simon: Virtual Embedding Networks for Vector Network Analyzer
ZVR, Appl. Note 1EZ45_0E, 23 September 1998.
[17] J. Ganzert: Controlling External Generators and Power Meters with Network
Analyzer ZVR, Appl. Note 1EZ46_0E, October 1998.
[18] A. Gleißner: Using the Frequency Conversion Mode of Vector Network
Analyzer ZVR, Appl. Note 1EZ47_0E, 18 January 1999.
[19] O. Ostwald: Measurement Accuracy of Vector Network Analyzer ZVK Appl.
Note 1EZ48_0E, 24 January 2001.
[20] J. Simon: Reading and Modifying the Correction Data for System Errors and
Power of a ZVR Vector Network Analyzer, Appl. Note 1EZ47_0E, 19 April
2001.
1EZ50_0E
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Rohde & Schwarz
Mixer Measurements
7 Additional Information
Comments and suggestions regarding this Application Note should be sent
to [email protected]
8 Ordering Information
Vector Network Analyzer
ZVK
10 MHz to 40 GHz
1127.8651.60
Vector Network Analyzer
ZVM
10 MHz to 20 GHz
1127.8500.60
Vector Network Analyzer
ZVC
20 kHz to 8 GHz
1127.8600.60/61/62
Vector Network Analyzer
ZVCE
20 kHz to 8 GHz
1127.8600.50/52
Vector Network Analyzer
ZVR
9 kHz to 4 GHz
1127.8551.61/62
Vector Network Analyzer
ZVRE
9 kHz to 4 GHz
1127.8551.51/52
Vector Network Analyzer
ZVRL
9 kHz to 4 GHz
1127.8551.14
ROHDE & SCHWARZ GmbH & Co. KG . Mühldorfstraße 15 . D-81671 München . Postfach 80 14 69 . D-81614 München
Tel (089) 4129 -0 . Fax (089) 4129 - 13777 . Internet: http://www.rohde-schwarz.com
.
This application note and the supplied programs may only be used subject to observance of the conditions of use set forth
in the download area of the Rohde & Schwarz Website.
1EZ50_0E
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