Using the Berkeley Nucleonics Signal Generators as external sources for Anritsu VectorStar™ VNAs

Berkeley Nucleonics Signal Generators with option GPIB support all GPIB features, commands and queries required by the VectorStar™ system. That enables using them as external sources.

• Option GPIB
• Firmware 0.4.123 or later

For time base synchronization use a BNC cable to connect VNA reference output "10 MHz OUT" and Signal Generator reference input "REF IN" as shown in figure 1.

• The VectorStar™ system expects external sources to listen to specific GPIB addresses. The default setting is:
  • external source 1 at GPIB address 4
  • external source 2 at GPIB address 5
  • external source 3 at GPIB address 2
  • external source 4 at GPIB address 3
  Use the Berkeley Nucleonics GUI to set the GPIB address of Berkeley Nucleonics Signal Generators. This is shown in figure 3. This setting is stored and remains unchanged upon power up and *RST. Note that the generator must be turned off and on for the new setting to become active. Alternatively, the VectorStar™ VNA can be configured to use different external source addresses. Refer to the VectorStar Operation Manual [1] for details.
• It is recommended that all external sources are locked to the reference of the VectorStar™ system. Use the Berkeley Nucleonics GUI to configure the generator for 10 MHz external reference as shown in figure 4. This configuration can be stored as the power up default. See figure 5.

Application → Rcvr Config → Multiple Source → Ext. Src Control

where a

State[Active/Inactive]

button shows up for each detected source. Then turn the external source to active state to use it.

If an external source is not detected, check the GPIB cable, check the sources GPIB address configuration or power cycle it.

Mixer downconversion loss shall be measured at

• a fixed IF of 30 MHz
• an RF range of 1 to 18 GHz
• a fixed RF input power level of -10 dBm
• a fixed LO level of +7 dBm

A Model 845-20 is used as the external source generating the 0.97 to 17.97 GHz swept LO signal (low-side LO, RF minus the 30 MHz IF).

The setup steps are:

1. Configure the Model 845-20 as explained under "Signal Generator setup".
2. Confirm that the VNA detects it as explained under "VNA setup".
3. Open the mixer measurement configuration dialog (figure 7). On the VNA:

   Application → Mixer → Mixer Setup (Active Channel)

   The dialog opening lets the user enter the setup.

   1. Check the port assignments: Mixer RF connects to VNA port 1, IF to port 2 and LO to external source 1.
   2. Configure frequencies and frequency ranges:
      • RF frequency mode "swept", range 1 to 18 GHz
      • LO frequency mode "auto"
      • IF frequency mode "fixed", at 30 MHz
   3. Define power levels:
      • RF power -10 dBm
      • LO power +7 dBm

   When done, the VNA will configure the external source automatically.

4. The receiver port can now be calibrated. In this example we skip the driver power calibration and perform a minimal through line calibration instead.
   1. Replace the mixer RF-IF path with a through line.
   2. Run the through line calibration:

      Calibration → Calibrate → Manual Cal. → RcvrCal./Normalization → Thru → 1-2

   3. Connect the mixer again.

   In addition, power and match calibration shall be performed to get accurate results. Refer to the VectorStar Calibration and Measurement Guide [2] for details.

5. Classical S-parameters are not useful in setups with different port frequencies. Instead the trace displayed can be configured to show scalar measurements. In typical mixer measurements the scalar B2/1 (port 2 received power) response is relevant.

   The active trace can be configured under:

   Response → User defined

   then select

   • Numerator: B2
   • Denominator: 1
   • Driver port: Port 1

   The resulting plot (figure 8) shows scalar mixer downconversion loss.