The Vector Mixer Meas submenu is used to assess the parameters of an external mixer including phase, e.g. the complex conversion loss or reflection coefficients. Compared to scalar mixer measurements, vector mixer measurements require an extended test setup and calibration method. Vector mixer measurements also require option R&S ZVA-K5, Vector Mixer Calibration. Moreover, the hardware options R&S ZVA<n>-B16, Direct Generator/Receiver Access, must be fitted.
Vector mixer measurements
In contrast to scalar mixer measurements, vector mixer measurements provide magnitude and phase information, including group delay, about the mixer under test (MUT). To assess the phase information, the IF signal at the mixer output is converted back to the original RF frequency using a second MEAS mixer. A third REF mixer ensures that the reference wave is converted back to the RF frequency. The test setup also requires a high or low pass filter and a power splitter.
Vector mixer measurements are performed between ports 1 and 2 of the network analyzer. Port 1 is assigned to the RF port of the mixer under test, port 2 to the IF port. Due to the two additional mixers, the frequencies of the measured waves a1, a2, b1, and b2 are all equal so that S-parameters and other quantities can be interpreted in the usual way, in analogy to the parameters of a non frequency-converting network. The LO signals for the MUT and the additional mixers can be provided by additional analyzer ports (port3, port 4, if available) or by external generators.
With the extended test setup, calibration becomes an important issue: In addition to the power calibration of the source signals, a complete two-port calibration at ports 1 and 2 (mixer vector calibration) is required to compensate for the effects of the additional components and shift the reference plane towards the ports of the mixer under test.
In the vector mixer mode the analyzer provides the following functionality:
Configuration of the RF and LO signals and measurement of the generated IF signal, see Define Mixer Mode andVector Mixer Test Setup.
Power calibration of all signal sources; see Mixer Power Calibration.
Full two-port calibration of the test setup including the two additional mixers; see Mixer Vector Calibration.
The vector mixer mode can be used to test important performance parameters of RF mixers such as frequency ranges, conversion loss, compression, and isolation.
Define Vector Mixer Meas... opens a dialog to configure the mixer input signals.
Vector Mixer Meas and Reset Frequency Conversion toggle between the (frequency-converting) vector mixer mode and normal (non frequency converting) operation.
Mixer Power Cal... opens a dialog to perform a power calibration of the signal sources and of the IF receiver.
Mixer Vector Cal... initiates a two-port calibration of the extended test setup including the two additional mixers and the low pass or high pass filter.
Opens a configuration dialog for the mixer input signals and indicates the extended test setup.
In the upper part the Define Mixer Measurement dialog shows a diagram with the test setup for vector mixer measurements. Below the dialog provides the following control elements:
Two port selection lists contains all analyzer ports or external generators which can provide the local oscillator (LO) signals. Ports no. 1 and 2 are always used for the RF signal and the measured IF signal (mixing product), so they are not included in the lists. Generators must be configured explicitly in the System Configuration – External Generators dialog before they appear in the lists. None means that a LO generator is not controlled by the analyzer. A power splitter is required to supply both the MEAS and the REF mixer ("Aux Mixer") with a LO signal (termed "Aux LO") from a single source. With a second splitter or a 3-way splitter, it is possible to supply all three mixers from a single source.
Aux Mixer selects one of two alternative test setups, with the MEAS and REF mixers connected to either port 2 or port 1.
Config Ext. Generators... opens the System Configuration – External Generators dialog for adding and configuring external generators.
Set Powers... opens a dialog to control the power of the RF and the LO signals.
Set Frequencies... opens a dialog to control the frequency of the RF and the LO signal and the analyzer (IF signal) frequency.
For network analyzers with upper frequency limits above 20 GHz, the lower IF frequency limit is 600 MHz, if the MEAS and REF mixers are connected to port 2. Change the test setup if the IF frequency falls below this limit.
Remote control:
[SENSe<Ch>:]FREQuency:CONVersion:MIXer:LOINternal <port_no> [SENSe<Ch>:]FREQuency:CONVersion:MIXer:LOEXternal <gen_no> [SENSe<Ch>:]FREQuency:CONVersion:MIXer:AINTernal NONE | <port_no> [SENSe<Ch>:]FREQuency:CONVersion:MIXer:AEXTernal NONE | <gen_no> [SENSe<Ch>:]FREQuency:CONVersion:MIXer:APORt <port_no>
The softkey Vector Mixer Meas activates the vector mixer mode, where the analyzer ports provide different source frequencies. Reset Frequency Conversion disables all frequency-converting measurements, including e.g. an active scalar mixer, mixer delay, or harmonic distortion measurement.
A Mix Frq RF label in the channel list indicates that a frequency-converting mode is active.
[SENSe<Ch>:]FREQuency:CONVersion VMIXer | FUNDamental
The mixer signal diagram shows the test setup including the mixer under test (MUT) and the two additional mixers ("Aux mixer")), the RF and LO signals, the mixing product (IF) with the necessary low or high pass filter, and the current frequency and power ranges for all signals. The diagram appears in the Define Vector Mixer Measurement dialog.
The mixer diagram changes along with the selected position of the MEAS and REF mixers. The example below corresponds to Aux Mixer: Port 2. The alternative diagram is symmetric, with the MEAS and REF mixers connected to port 1. See background information Finding the best test setup below.
The RF signal is the stimulus signal that the analyzer generates with the current channel settings. After a reset the frequency and power of the RF signal is as defined in the Channel – Stimulus menu. The RF signal parameters can be changed in the Set Power... and Set Frequencies... dialogs.
The Local Oscillator (LO) signals are two additional RF signals that are either generated by the network analyzer (at the ports that are not used for the RF and IF signals, i.e. port 3, 4...) or by external generators. Both LO signals are at the same frequency. The first LO signal is fed to the LO input of the MUT, the second to the additional mixers using an appropriate power splitter (not in the diagram). If necessary, appropriate amplifiers can be used in addition. With a second power splitter or a 3-way splitter, it is also possible to supply all three mixers from a single source. On four-port analyzers, it is recommended to use the (coupled) analyzer ports port 3 and port 4 for the LO signals.
The IF signal is the mixer output signal (mixing product), which is at one of the following frequencies: IF = |LO – RF|, i.e. LO – RF (for LO > RF) or IF = RF – LO (for RF > LO) or IF = LO + RF. The IF frequency band is selected in the Set Frequencies... dialog.
The low pass or high pass filter rejects the undesired mixing product that might impair the accuracy of the measurement and of the mixer vector calibration. The required filter type and cut-off frequency are displayed in the diagram, depending on the RF / LO frequencies and the selected IF band.
If the mixer under test is measured in down-converting mode (IF = RF – LO or IF = LO – RF), a low-pass filter must be used to reject the up-converted IF signal at IF = RF + LO. If fed to the IF input of the MEAS mixer, the RF + LO signal would be down-converted to RF, which would make it indistinguishable from the RF – LO signal, up-converted to RF. The cut-off frequency of the low-pass filter must be between Max(RF – LO) and Min(RF + LO).
If the mixer under test is measured in up-converting mode (IF = RF + LO), a high-pass filter must be used to reject the down-converted IF signal at IF = RF – LO. If fed to the IF input of the MEAS mixer, the RF – LO signal would be up-converted to RF, which would make it indistinguishable from the RF + LO signal, down-converted to RF. The cut-off frequency of the high-pass filter must be between Max(RF – LO) and Min(RF + LO).
The additional mixer MEAS converts the filtered IF signal from the mixer under test back to the RF frequency which is fed to the measurement receiver at port 2.
The additional mixer REF converts the IF signal from the internal source at port 2 to an RF signal which is fed to the reference receiver.
The signal description above with the swept RF signal and the LO signal at a fixed frequency corresponds to the default configuration. In the Set Frequencies dialog, you can select any of the signals as a Sweep/CW signal. You can set the frequency range of this signal via Start/Stop or CW Frequency. A second signal is at a Fixed frequency, and the third at the calculated sum or difference frequency (Auto).
The vector mixer measurement is also compatible with different sweep types, e.g. a power sweep. The labeling of the input and output signals of the MUT depends on the sweep type.
Finding the best test setup
The alternative test setups place different requirements on the NWA receivers and the additional equipment.
Test setup (Aux Mixer)
Receiver requirements
Low pass / high pass filter requirements
Port 2, forward measurement (port 1 --> port 2)
RF signal is converted to IF by the MUT and passes the coupler at NWA port 2 as well as the MEAS mixer before it reaches the measurement receiver.
--> Reduced accuracy for network analyzers with an upper frequency limit > 20 GHz and IF frequencies <600 MHz.
The distance between the two IF bands increases with the LO frequency.
--> Moderate filter requirements for "standard" measurement scenarios where fRF >> fIF, fLO >> fIF.
Port 2, reverse measurement (port 2 --> port 1)
No limitations
n/a
Port 1, forward measurement (port 1 --> port 2)
Port 1, reverse measurement (port 2 --> port 1)
IF signal is converted to RF by the MUT and passes the coupler at NWA port 2 as well as the MEAS mixer before it reaches the measurement receiver.
--> Reduced accuracy for network analyzers with an upper frequency limit > 20 GHz and RF frequencies <600 MHz.
The distance between the two RF bands decreases if a smaller IF frequency is chosen.
--> High filter requirements for "standard" measurement scenarios with low IF frequencies.
Avoid test setup "Port 2", if you use a network analyzer with an upper frequency limit > 20 GHz and work at IF frequencies <600 MHz.
Avoid test setup "Port 1", if the edge of your low pass or high pass filter is not steep enough to clearly separate the two RF bands in the reverse measurement.
Example: RF frequency: 1.1 GHz ... 1.2 GHz, LO Frequency: 1.0 GHz, IF = RF – LO (Down, USB). An R&S ZVA24 network analyzer is used.
--> IF = 100 MHz ... 200 MHz. For best accuracy in the forward measurement, use test setup "Port 1". In the reverse measurement, this test setup requires a high pass filter with a cutoff 900 MHz < fc < 1.1 GHz.
Opens a dialog to perform a power calibration of the signal sources and of the IF receiver. A power calibration ensures accurate levels of the mixer input signals (RF, IF, and LO source power calibration). The necessary calibration steps are automatically performed across the entire frequency range of the active mixer measurement (Set Frequencies).
Mixer Power Cal procedure and example
Due to the different frequency ranges of the input and output signals and the external equipment needed, the mixer power calibration must be performed in several steps. For the standard test setup where the RF and LO signals are provided by port 1 and an external generator, respectively, where the RF signal is swept, and where the IF signal is analyzed at port 2, the following test setups are required:
Source power calibration for the RF signal. A power sensor is connected to port 1. The RF power (red) is calibrated over the selected RF sweep range.
Source power calibration for the IF signal. A power sensor is connected to port 2. The IF power (red) is calibrated over the IF sweep range, calculated from the selected RF sweep range and the LO frequency. No additional external devices such as mixers are needed.
Source power calibration for the LO signal, provided by an external generator. A power sensor is connected to the generator's RF output (red signal). The analyzer controls the generator, its RF power (red) is calibrated at the selected IF frequency. No RF connection to or from the network analyzer is needed.
Take Cal Sweep in the three numbered panels starts the calibration sweeps for the RF source, IF source, and the LO source, respectively. The measured power is shown in the diagram in the center of the dialog and the sweep progress in the progress bar below.
Abort Sweep stops the current sweep, e.g. in order to change the sweep settings.
The calibration sweeps are performed according to the settings shown in the Settings panel in the upper right section of the dialog. Modify Settings opens the Modify Source Power Cal Settings dialog to modify the essential settings of the next calibration sweep.
Power Meter selects an external power meter that is used to measure the exact source power at the calibration point; see Power Meter Settings. Power meters (Pmtr1, Pmtr2, ...) must be configured in the System Configuration – External Power Meters dialog before they appear in the list.
Perform Verification Sweep after Cal enables or disables a verification sweep that the analyzer performs after each source power calibration. The sweep is also displayed in the calibration sweep diagram. Its purpose is to test the accuracy of the source power calibration after the final correction data has been acquired.
Opens a submenu to perform a 2-port calibration (system error correction) for vector mixer measurements. The calibration can be performed manually or using a calibration unit.
Manual Cal... opens the Calibration wizard for two full one-port calibrations at ports 1 and 2.
Calibration Unit... opens a dialog for (partially) automatic calibration using the connected calibration unit.
Both calibration methods provide equivalent results.
Opens the calibration wizard to perform a 2-port calibration (system error correction) for vector mixer measurements. The calibration is performed with the complete test setup including the additional mixers MEAS and REF and the high pass or low pass filter. The mixer under test (MUT) is simply replaced by the required calibration standards. The effect of the calibration is to shift the reference plane to the MUT ports as shown below (red lines represent the reference plane without calibration and with closed jumper connectors, green lines represent the reference plane after calibration).
Due to the frequency-converting properties of the vector mixer measurement, the factory calibration is not applicable and therefore suspended. The Measure Standards calibration dialog shows uncorrected, raw measurement results; the mixer vector calibration is based on these results. A proper mixer vector calibration is essential for an accurate vector mixer measurement.
The mixer vector calibration corresponds to a 2-port UOSM calibration where the unknown through standard is replaced by an unknown calibration mixer. In analogy to the unknown through standard used for UOSM calibration, the calibration mixer must be reciprocal (S21 = S12).
If your mixer under test is reciprocal, you can also use it as a calibration mixer.
See also calibration wizard description.
Opens a dialog for automatic vector mixer calibration using the connected calibration unit.
The dialog shows the active calibration unit and characterization. Click Change Active Calibration Unit or Characterization... to change these settings. The port assignment displayed in the center of the dialog must not be changed.
The automatic calibration procedure is analogous to manual calibration, however, automatic calibration involves only two steps:
The active cal unit provides the one-port standards for ports 1 and 2. Connect the cal unit between ports 1 and 2 and click the left Take Cal Sweep button to obtain all necessary one-port correction data at once.
The calibration unit does not provide any frequency-converting calibration standards. Connect a reciprocal calibration mixer between ports 1 and 2 and click the right Take Cal Sweep button to obtain the missing 2-port correction data.
The order of the calibration sweeps is arbitrary. Click Apply to start the calculation of the system error correction data and apply the calibration to the active channel.