Before conducting a measurement in Vector Voltmeter mode, select a CW frequency and perform a calibration. During calibration, choose between a 1‑port or 2‑port calibration depending upon whether return or insertion type measurements (respectively) are desired.
The choice of whether to use a 1-port or a 2-port measurement is usually dictated by the physical site configuration. If the DUT (device under test) is compact, such as cables or amplifiers or filters, then the 2-port measurement may be used because both ends are available near the Vector Network Analyzer. If a cable is already installed permanently, then the 1-port methods are indicated because only the one end of the DUT is convenient to the test port.
When making a 1‑port connection to the DUT, select the Return measurement type and perform a 1‑port calibration. When making a 2‑port connection to the DUT, select the Insertion measurement type and perform a 2‑port calibration. The following paragraphs further explain these steps.
How the VVM Function Works
1. Insertion technique (2-port). One technique uses the Vector Network Analyzer in a straightforward manner with its 2-port setup. By characterizing the insertion phase delay of a signal by measuring S21 or S12 through the cable, the operator can determine the phase shift of the component or cable from input connector to output connector. The Vector Network Analyzer Option 15 display presents those S21 or S12 data as insertion loss in dB and insertion phase in degrees.
2. Reflection technique (1-port). The second technique (using the Vector Network Analyzer) measures the S11 or S22 reflected signal on a component or cable, and depends upon the procedure in which the far end of the cable is deliberately mismatched, either shorted or left open‑circuited. This reflects virtually 100 % of the input signal, and the phase delay of the measured reflected signal is therefore equal to twice the one-way phase of the cable. Likewise, the cable attenuation is twice the one-way loss. This technique is especially useful for situations in which you must manually create multiple phase matched cables. This would be done by carefully snipping small amounts of cable with a diagonal cutters, perhaps 1/8th inch at a time, and re-measuring the effect on the 2-way phase.
Note
The MS20xxC VNA Master features a fully-reversing architecture, which allows for measurements (on Port 1 and Port 2) of all four S‑parameters without reconnecting the DUT. With Option 15 VVM, you can make a Return measurement type (amplitude and phase) on either Port 1 (S11) or Port 2 (S22). Similarly, you can make an Insertion measurement type (amplitude and phase) either with Port 1 transmitting (S21) or with Port 2 transmitting (S12). You select the Port using the Cal Port soft key under the CW menu. When making Return measurements, you can connect two cables (one to each port) and then toggle the Cal Port setting to look at the Return results of both cables without having to disconnect and reconnect.
Simple Measurement Using CW Display
1. Press Shift and Mode and Enter to use the Vector Voltmeter function.
2. Press the CW function hard key.
3. Press CW Frequency soft key and enter the desired frequency.
4. Press the Cal function hard key.
5. Press the Cal Type soft key and select the type of calibration from the selection list box.
6. For typical VVM applications, the Cal Method should be SOLT, and the Cal Line Type should be Coax.
7. Press the DUT Port Setup soft key to select a specific connector type for each port. Select (from the list) the connector type of the device under test (or equivalently, the calibration component connector type).
8. Press the Start Cal soft key to begin the calibration. Figure: 1‑Port Calibration, using MS2024B shows a typical setup for a 1‑port Open‑Short‑Load calibration at Port 1.
For two‑port measurements, refer to Figure: 2‑Port Calibration, using MS2028C, which shows a setup for 2‑port calibration using Open‑Short‑Load‑Isolation‑Through. In order to ensure a good calibration, be careful to follow the on‑screen instructions for connecting the calibration components.
9. After calibration, press the CW function hard key to display the CW menu.
10. Connect the DUT for measurement at the desired Port. The display should appear similar to the image in Figure: Continuous Wave Menu – MS20xxC VNA Master. The measurements and display parameters on your instrument display may differ from those in this user guide.
11. Specify Measurement Type to be Return for a 1-port DUT. After a 2-port calibration, both Return and Insertion measurement types can be viewed.
12. Choose to view the measurement results for the return measurement as dB, VSWR, or Impedance by pressing the Return Meas. Format soft key. For insertion measurements, only the dB selection is available.
13. Choose the Cal Port to be Port 1 or Port 2. If you performed a Full S11 calibration, then choose Port 1 to have that calibration apply. If you performed a Full S22 calibration, then choose Port 2 to have that calibration apply. If you performed a Full S11 and S22 calibration, or a full 2-Port calibration, then you will be able to make calibrated measurements using both Port 1 and Port 2. For Insertion measurements on a symmetric cable with a full 2-Port calibration, using Cal Port 1 or Cal Port 2 should give you the same results.
This completes the procedure for performing a simple measurement using the Vector Voltmeter mode.