The Scalar Mixer Meas submenu controls the measurement of the mixing products generated by an external mixer that is supplied with two independent RF signals. Together with the Harmonic Distortion measurement and the arbitrary configuration of generator and receiver frequencies (Port Configuration), the scalar mixer mode is included in option R&S ZVA-K4.
Mixer Measurements
RF mixers convert an RF signal at one frequency into a signal at another frequency. The frequency that is to be shifted is applied at the RF input and the frequency shifting signal (from a local oscillator, LO) is applied to the RF mixer's LO port, resulting in an output signal at the mixer's Intermediate Frequency (IF) port.
For a given RF signal, an ideal mixer would produce only two IF outputs: one at the frequency sum of the RF and LO (IF = RF + LO), and another at the frequency difference between the RF and LO (IF = |RF – LO|). A filter can select one of these IF outputs and reject the unwanted one.
The frequency-converting property of the mixer (i.e. the fact that incident and transmitted waves are at different frequencies) causes a loss of phase information. In fact, transmission S-parameters obtained in a scalar mixer measurement only describe the magnitude ratios of the waves. The phase information, including the group delay, is meaningless.
In the 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 andMixer Signal Diagrams.
Power calibration of the signal sources and of the IF receiver; see Mixer Power Calibration.
The mixer mode can be used also to test important performance parameters of RF mixers such as frequency ranges, conversion loss, compression, and isolation.
Define Scalar Mixer Meas... opens a dialog to configure the mixer input signals.
Scalar Mixer Meas and Reset Frequency Conversion toggle between the (frequency-converting) mixer mode and normal (non frequency converting) operation.
Enhanced Scalar Mixer Meas activates the measurement mode with an additional enhanced wave calibration at the RF and IF ports (Port 1, Port 2).
Mixer Power Cal... opens a dialog to perform a power calibration of the signal sources and of the IF receiver.
Scalar Mixer Meas Cal opens a submenu to perform the system error corrections which are required for the enhanced mixer measurement.
This dialog configures the mixer input signals.
In the upper part the Define Mixer Measurement dialog shows a diagram with the RF and LO signals, the mixing product (IF), and the current frequency and power ranges for all signals. Below the dialog provides the following control elements:
The port selection list contains all analyzer ports or external generators which can provide the local oscillator (LO) signal. 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 list. Generators must be configured explicitly in the System Configuration – External Generators dialog before they appear in the list. None means that the input signal at LO (if available) is not controlled by the analyzer.
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.
Remote control:
[SENSe<Ch>:]FREQuency:CONVersion:MIXer:LOINternal <port_no> [SENSe<Ch>:]FREQuency:CONVersion:MIXer:LOEXternal <gen_no>
The softkey Scalar Mixer Meas activates the scalar mixer mode, where the analyzer ports are at different frequencies. Reset Frequency Conversion disables all frequency-converting measurements, including e.g. an active harmonic distortion measurement.
A Mix Frq RF label in the channel list indicates that a frequency-converting mode is active.
[SENSe<Ch>:]FREQuency:CONVersion MIXer | FUNDamental
Activates the mixer measurement mode with an additional enhanced wave correction at the RF and IF ports (Port 1, Port 2). The enhanced mixer measurement requires two full one-port calibrations at the RF and IF ports, in addition to a scalar mixer measurement power calibration.
The enhanced mode improves the accuracy of the scalar mixer measurement but does not provide any additional results. The phase or group delay of mixers can be analyzed in a vector mixer measurement. When an enhanced scalar mixer measurement is active and all necessary calibrations are available, the trace line for the conversion loss b2/a1 shows the calibration labels Pcal Cal.
Proceed in the following order to activate the enhanced scalar mixer measurement:
1. Open the Define Scalar Mixer Meas... dialog to activate the mixer measurement mode.
2. Select Scalar Mixer Meas Power Cal... to perform the power calibrations at ports 1 and 2.
3. Select Scalar Mixer Meas Cal > to perform the necessary full one-port calibrations.
4. Activate Enhanced Scalar Mixer Meas.
Enhanced wave correction for scalar mixer measurements
The enhanced wave correction for the scalar mixer measurement calibrates the a- and b-waves at the RF and IF ports of the mixer under test. The RF and IF frequencies are different from each other. Two steps are required to calibrate each of the ports 1 and 2:
A full one-port system error correction calibrates the phase and relative power of the waves.
A source or receiver power calibration determines the absolute amplitude of the a- or b-waves. Together with the full one-port calibration, this yields the absolute power of all waves.
The order of the calibration steps is arbitrary. A Scalar Mixer Measurement Power Calibration provides a source power calibration for port 1 and a receiver power calibration for port 2. The Scalar Mixer Meas Calibration provides both full one-port calibrations.
The one-port calibrations for the two ports are completely independent; the calibration does not involve a through-connection between the ports. Alternatively, it is possible to perform a single full two-port calibration at ports 1 and 2 as shown in section Enhanced Wave Correction Procedure. The analyzer will perform segmented calibration sweeps and discard the calibration data of the Through standard.
[SENSe<Ch>:]CORRection:EWAVe[:STATe]
The mixer signal diagrams show the parameters of the mixer input signals (RF, LO) and of the mixing product (IF signal, output). The diagrams appear in the Mixer Measurement, Set Power, and Set Frequencies dialogs.
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) signal is an additional RF signal that is either generated by the network analyzer (at one of the ports that are not used for the RF and IF signals) or by an external generator.
The IF signal is the mixer output signal (mixing product), which is at one of the following frequencies: IF = LO + RF or IF = |LO – RF|, i.e. LO – RF (for LO > RF) or IF = RF – LO (for RF > LO). The IF frequency is selected in the Set Frequencies... dialog.
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 labeling of the complete diagram depends on the sweep type.
Frequency sweep
For a frequency sweep, the signal diagram is labeled as follows:
RF signal: Fixed port number (1), CW power, frequency sweep range.
LO signal: Signal source (analyzer port or external generator), fixed power and frequency.
IF signal: Fixed port number (2), frequency range = (sweep range + LO) or |sweep range – LO|.
Power sweep
For a power sweep, the signal diagram is labeled as follows:
RF signal: Fixed port number (1), power sweep range (or fixed power, if the LO signal is swept), CW frequency.
LO signal: Signal source (analyzer port or external generator), fixed power (or power sweep range, if the RF signal is at a fixed power), CW frequency.
IF signal: Fixed port number (2), fixed frequency = (RF + LO) or |RF – LO|.
Time or CW mode sweep
For a Time or CW Mode sweep, the signal diagram is labeled as follows:
RF signal: Fixed port number (1), fixed power, CW frequency.
LO signal: Signal source (analyzer port or external generator), fixed power, CW frequency.
The Set Power dialog defines the power of the RF and the LO signals.
The diagram contains the mixer signal diagram and the following control elements:
The RF Power or LO Power radio button groups specify how the power for each signal is defined. The roles of the mixer input signals RF and LO are interchangeable: One signal is at the analyzer's channel power (Sweep or CW, the signal is swept if a power sweep is active; it is at fixed power (CW) for the other sweep types), the other is at the Fixed power defined below.
The input fields in the Sweep or CW Power panel (depending on the sweep type) define the channel power and overwrite the power settings in the Channel – Stimulus and Channel – Power Bandwidth Average menus. The sweep range or CW power is assigned to the signal with Sweep/CW power definition. Enter & Display can be used to select the Swept or Auto port for display and entry. Note: If you select the Fixed port, this port will be set to swept.
Fixed Power defines the power of the signal with Fixed power definition. For vector mixer measurements, the power of the Aux LO signal (fed to the MEAS and REF mixers) can be defined independently.
SOURce<Ch>:]FREQuency:CONVersion:MIXer:FUNDamental RF | LO SOURce<Ch>:]FREQuency:CONVersion:MIXer:PFIXed <power> SOURce<Ch>:]FREQuency:CONVersion:MIXer:PAFIXed <power>
Controls the frequency of the RF and the LO signal and the analyzer (IF signal) frequency.
The RF/IF/LO Frequency radio button groups specify how the frequency for each signal is defined. The roles of the three signals RF, IF, LO are interchangeable: One signal is at the analyzer's channel frequency (Swept/CW, this signal is swept if a frequency sweep type is active; it is a CW signal for the other sweep types), the second is at the Fixed frequency defined below, the frequency of the third signal is automatically calculated according to the selected Conversion formula.
The input fields in the Swept Frequency panel define the channel frequency and overwrite the Channel – Stimulus settings. The signal in the Enter & Display field becomes the Swept signal, with the sweep range or CW frequency defined below. The two other signals are adjusted as described above.
Fixed Frequency defines the frequency of the signal with Fixed frequency definition.
Conversion selects the frequency of the signal with Auto frequency definition, see background information below.
Conversion formulas
The IF signal can be at the sum or at the difference of the RF and LO frequencies.
IF = RF – LO means that the RF signal is down-converted (upper sideband). The analyzer automatically switches to IF = LO – RF if the LO frequency is above the RF input frequency.
IF = LO – RF means that the LO signal is down-converted (lower sideband). The analyzer automatically switches to IF = RF – LO if the RF input frequency is above the LO frequency.
IF = LO + RF means that the RF input signal is up-converted.
To perform measurements at different mixer output frequencies (e.g. to analyze the isolation for IF = RF or higher-order mixing products), use option R&S ZVA-K4, Arbitrary Generator and Receiver Frequencies.
In a frequency sweep mode where one of the input frequencies varies over a definite range, the IF signal also covers a frequency range of the same width. An error message is displayed if the IF frequency exceeds the maximum frequency range of the analyzer.
If the RF or LO signal is in Auto mode, the formulas for IF are automatically converted, and the analyzer calculates the RF or LO frequency from the other frequencies.
[SENSe<Ch>:]FREQuency:CONVersion:MIXer:FFIXed <frequency> [SENSe<Ch>:]FREQuency:CONVersion:MIXer:FIXed RF | IF | LO [SENSe<Ch>:]FREQuency:CONVersion:MIXer:FUNDamental RF | IF | LO [SENSe<Ch>:]FREQuency:CONVersion:MIXer:TFRequency DCLower | DCUPper | UCONversion [SENSe<Ch>:]FREQuency:STARt etc.
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 and LO source power calibration) and an accurate power measurement of the mixer output signal (IF receiver 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 a test setup where the RF and LO signals are provided by port 1 and an external generator, respectively, where the RF signal is swept, the LO signal is at fixed frequency, and where the swept 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. As a preparative for step 2 the analyzer also calibrates the source in the IF frequency range. The correction data for both calibration sweeps is stored.
Receiver power calibration for the IF signal. No external device is needed. The receiver (port 2) is calibrated in the IF frequency range using the source signal from port 1 (red) calibrated in the first step.
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. The generator's RF source power (red) is calibrated at the selected LO frequency. No RF connection to or from the network analyzer is needed.
Take Cal Sweep in the three numbered panels start the calibration sweeps for the RF source, IF receiver, 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 the system error corrections which are required for the enhanced mixer measurement. The calibration can be performed manually or using a calibration unit.
Manual... opens the Calibration wizard for two full one-port calibrations at ports 1 and 2.
Calibration Unit... opens the Calibration Unit dialog for automatic calibration using the connected calibration unit. The pre-selected calibration type is compatible and port combination is suitable for the scalar mixer measurement.
Both calibration methods provide equivalent results.