Distributed VNA Measurement (S9x571B)

Overview

This S9x571B application allows you to configure two VNA sets (PXI or Streamline) separated by up to 5 meters. This capability enables long‑distance S‑parameter measurements, such as cable testing and antenna characterization, while providing improved dynamic range and measurement stability.

Supported Model

• M980xA (M9834A/M9837A are not supported)

• P50xxB/M (P93xxB is not supported)

S9x551B Multiple instruments/modules measurements is also required.

Configuration

The Distributed VNA requires one reciprocal thru cable to make the Auto refresh Cal. The thru cable must be connected during measurements.

The DUTs can be connected on the other ports. The figure shows an example of Streamline VNA.configuration. If phase measurement is not required, The thru cable for Auto Refresh Cal is not necessary.
 

When your DUT is a thru cable, the cable for auto refresh calibration (ports 1 to 6 in this example) can be a DUT. In that case, the path for auto refresh cal must be connected during the measurements. Otherwise, "Auto Refresh cal is inactive" will be displayed.

Configuration for Streamline

Two units of Strealeamline VNA can be configured as shown in the figure above. 

The required accessories are: 

• Y1730A-500 3.5 mm cable (m-m), 5m
• Y1730A-510 Control Cable, 5m
• Y1710A-401 Thunderbolt 3 cable, 0.8 m
• Y1710A-402 Thunderbolt 3 cable, 5 m

Configuration for PXI 

The limitation of PXI configuration are:

• Two chassis only

• Up to five modules in one chassis (Total 10 module)

  • 6 port x M980xA: Up to 60 ports

The following two configurations are supported.

• M9038A (Chassis1, Slot1)  TBT Cable to  M9025A (Chassis2, slot1)

• Host Desktop PC with SP0630A – SP0633A PCIe Cable –SP0631A PCIe (Chassis1, Slot1) – Y1730A-520 PCIe Cable – SP0631A PCIe (Chassis2, slot1)

Please refer to configuration guide for the required components.

The following figure shows the configuration using PCIe Cable connection with an external host PC.

Measurement Procedure

1. Power on the two modules or chassis after configuration is completed (LO cables and control cables must be connected before power on)

2. Launch the VNA application

3. Activate the Distributed VNA.

4. Select the measurement class and setup your desired measurement setting.

5. Execute the calibration

6. Turn on Auto Refresh

7. Execute the DUT measurements

Activate Distributed VNA

To activate the distributed VNA feature

1. Click Setup > Internal Hardware > Distributed VNA, then Distributed VNA dialog box is displayed

2. Check Enable distributed VNA, then click OK.

3. Preset is done.

4. DistVNA is displayed in the status bar.

Setup the measurement setting 

Set up your desired settings. Auto Refresh Cal has the following limitations. If phase measurement is not required, ignore this limitation because Auto Refresh Cal is unnecessary.  

Reciprocal Thru Cable Insertion Loss

If the reciprocal thru is too lossy, measurement errors increase and Auto Refresh Cal may not function correctly. To minimize measurement errors, the following conditions are recommended:

• Output Power ≧ -5 dBm

• IFBW ≦ 100 kHz

• Reciprocal thru cable loss < 20 dB

For M980xA, P500xB, P502xB, and P502xM (x = 5–8), meet these conditions from 500 kHz to 50 GHz.

If the reciprocal thru is too lossy, the following warning is displayed and no correction is applied. This warning also is displayed when a reciprocal thru cable is not connected.

"Auto Refresh Cal is inactive. Path Px-x is too lossy."

When using a reciprocal thru cable with loss exceeding 20 dB, this warning may appear but you can disable it by clearing the Check Path checkbox. However, do so with caution and compensate by tightening other measurement condition, such as increasing Output Power above −5 dBm, reducing IFBW below 100 kHz, and enabling Averaging (or increasing the averaging factor). For example, if the reciprocal thru loss is 30 dB (20 dB limit + 10 dB), increase Output Power by 10 dB to +5 dBm, or reduce IFBW by a factor of 10 Hz to 10 kHz, or increase the averaging count by a factor of 10 to 10 averages.

Frequency Range

For M980xA, P500xB, P502xB, and P502xM (x = 5-8), measurement errors are large below 500 kHz and above 50 GHz. In these ranges, Auto Refresh Cal uses measurement values from other frequencies to perform the correction. Therefore, correction cannot be applied if the measurement range is entirely below 500 kHz or entirely above 50 GHz, because no usable in-range frequency points are available for the correction. Set Frequency Start to 50 GHz or below and Frequency Stop to 500 kHz or above. If these conditions are not met, the following warning is displayed and no correction is applied:
"Auto Refresh Cal is inactive. Frequency Range cannot be corrected."

Number of Points

If the calibration is executed while at a distance for two units, Number of Point should meet the criteria

Execute Calibration

If two VNA sets can be placed closely during the calibration, the calibration steps can be reduced. Hence, there are two cases for calibration.

Case 1: Two VNA sets placed (PXI or Streamline) separated.

The calibration step is as shown blow. Confirm if the number of points meets the required condition before the calibration.

1. Click Cal > Main > Smart Cal (or Cal > Main > Other Cals > ECal... for ECal)

2. Select the required calibration ports and options. Then,

3. Define the Connector, DUT gender and Cal Kit. Check the "Modify Cal Type". Then, click Next for the next dialog.

4. Define the 1st port and 2nd port for each thru. 

   1. Assign one port as a key 1st Port in the module (or Chassis) No.1.  In the example below, port 1.

   2. Assign each other ports in module No. 1 as 2nd port as "ECal Thru as Unknow thru" for Ecal, or "Unknown Thru" for mechanical cal kits. 

      • Thru #1: 1-2

      • Thru #2: 1-3

      • Thru #3: 1-4

   3. Assign one port in the module No.1 and one port in the module No.2 as Unknown Thru.

      • Thru #4: 1-6 

   4. Assign one port as a key 1st port in the module (or chassis) No.2. In the example below, port 5

   5. Assign each other ports in module No. 2 as 2nd port as "ECal Thru as Unknown thru" for Ecal, or "Unknown Thru" for mechanical cal kits. 

      • Thru#5: 5-6

      • Thru#6: 5-7

      • Thru#7: 5-8

   6. Click Next for the next dialog.

5.   Follow the instruction to execute the calibration.

Note: During the Thru measurement in step 4c (Thru #4: 1-6), do not move the long LO cable connecting the two modules.

Note: When using the ECal, a long USB cable is required to reach the remotely located VNA. A powered USB hub is also necessary to provide sufficient power to the ECal. Connect a long USB cable to the PC, with a powered USB hub at the other end, to which the ECal is connected. 

 Example 1: Streamline 8 port configuration. Ports 1 to 4 in the module No.1, ports 5 to 8 in the module No.2

Example 2: PXI 20 port configuration , Ports 1 to 10 in the chassis No.1, Ports 11 to 20 in the chassis No.2   

Required Number of Point

As this calibration uses a long thru cable, the unknown thru calibration requires larger number of points to determine the cable length.

Example Calculation

• Frequency span = 50 GHz

• hru cable length = 5 m

• Cable type = polyethylene cable (Vf = 0.66)

Step 1: Calculate the maximum Δf

Δf < (0.66 × 2.997925E8 ) / (4×5)

Δf < 9.8 MHz
 

Step 2: Calculate the minimum number of points
number of points > (50  GHz / 9.8  MHz)+1

number of points >= 5103

Thus, at least 5103 points are required for the analyzer to automatically determine the Thru cable delay.

Reference for maximum Δf calculation

The maximum allowable frequency step (Δf) for automatic Thru cable delay estimation is determined using the following formula:

   Δf<(V_f × c) / (2×l)

Where:
    l = physical length of the Thru cable (meters)
    Δf = frequency step size = span / (points − 1)
    Vf = velocity factor of the Thru cable
    c = speed of light = 2.997925 × 10⁸ m/s

A smaller Δf (i.e., more measurement points) enables the instrument to accurately determine the electrical delay of the Thru cable.

Case 2: Two VNA sets can be moved closely during calibration 

If the two VNA sets can be moved at the same place during calibration, there are the following benefits.

• No requirement for Number of Points.(A short thru cable can be used)

• Fewer calibration steps.

• A powered USB hub and long USB cable are not required for ECal

The calibration steps are the same as Case 1, with the following difference:

When assigning the cross-module thru (Thru #4: 1-6), select "ECal Thru as Unknown Thru" for ECal, or "Unknown Thru" for mechanical cal kits — the same as all other thru assignments.

Note: During the Thru measurement in step 4c (Thru #4: 1-6), do not move the long LO cable connecting the two modules. 

Example 1: Streamline 8 port configuration. Ports 1 to 4 in the module No.1, ports 5 to 8 in the module No.2

Example 2: PXI 20 port configuration , Ports 1 to 10 in the chassis No.1, Ports 11 to 20 in the chassis No.2   

Activate Auto Refresh Cal

Auto Refresh Cal compensates the phase drift of local signal due to a cable movement and temperature change. 

1. Click Cal > Other Cals > Auto Refresh Cal...

2. Select the thru path for auto refresh cal.
   

3. Check Enable Auto Refresh, then click OK.

4. Disable if Check Path function is not required.

5. ARefresh is displayed in the status bar.

Execute the DUT measurements

• Connect the DUT on the calibrated port and execute measurements

• The thru cable for Auto Refresh Cal must be connected during the measurements.

• "Refresh Cal is active" is displayed when the auto refresh cal works correctly

• There is the following warning messages for Refresh Cal

  • Auto Refresh Cal is inactive. Path Px-x is not reciprocal.

    • Verify that a reciprocal thru is connected to path Px-x.

    • This warning can be disabled by unchecking “Check Path” or by “CALC:CORR:REFR:AUTO:CPAT:STAT”.

  • Auto Refresh Cal is inactive. Path Px-x is too lossy.

    • Verify that a thru is connected to path Px-x and that the thru cable does not have excessive loss.

    • This warning can be disabled by unchecking “Check Path” or by “CALC:CORR:REFR:AUTO:CPAT:STAT”.

  • Auto Refresh Cal is inactive. Frequency Range cannot be corrected.

    • Verify that there are measurement points within 500 kHz to 50 GHz.

    • Include at least part of 500 kHz to 50 GHz in the sweep range.

• “Refresh Cal is active” is displayed when the above warning is cleared and Auto Refresh Cal works correctly

Limitation

Supported Application and Feature

The following features are not supported.

• Direct  Receiver Access (Port Config.)
• Ref. In configuration
• Frequency Offset Measurements
• CalPod
• S94xxxB applications 
• Auto Refresh Cal cannot be applied to the following Cal Sets:
  • Cal Sets where new error terms were appended to an existing User Cal Set (see Appending Data in a Cal Set)
  • Cal Sets that were de-embedded or embedded (for example, those created using Cal Plane Manager or AFR)

Limitation for TDR

• Deskew and Loss Compensation is not supported. Only ECal is supported 
• MM Phase Cal is not supported.
• Auto Refresh Cal is available via SCPI commands. In the dialog interface, it is available only in Advance Mode.