Various 1‑port and 2‑port calibrations are available in the VNA Master. Transmission response is the simplest and requires only one connection during calibration, but it does not correct for test port match errors. 1‑Path 2‑Port calibration requires four calibration connections and corrects for the transmit port match, but does not correct for the receive port.
Note
The previously described calibration considerations omit isolation steps in which loads are connected to each test port. During the isolation step of the calibration procedure, the VNA Master measures the isolation between test ports in order to achieve best dynamic range performance.
The Vector Network Analyzer Calibration menu is the same one that is used in the Vector Voltmeter menu. Refer to section “Calibration Menus” in Chapter 5 of the Vector Network Analyzer Measurement Guide (refer to Supplemental Documentation) for more information about the calibration menu. Note that some calibration parameters are shared between the Vector Network Analyzer and Vector Voltmeter mode, and that some parameters are different because they were optimized for the specific mode application.
When you perform a calibration, the correction coefficients are calculated for specific S‑parameters (depending on the type of calibration chosen) and for instrument settings (frequency range, number of points, and power level). The term “calibration correction” refers to the measurement correction coefficients that are applied to measurements as a result of your calibration.
When calibration correction is On, the correction is applied to all applicable S‑parameters. For example, if a Full S11 (1‑port) calibration is performed, then only traces that measure S11 have a valid calibration. For those traces, the calibration information data in the Instrument Settings Summary (item 1 in Figure: VNA Master Overview) shows “CAL: ON (OK)”. All other traces that do not measure S11 display “CAL: --” to indicate that no valid calibration is available for those traces. The calibration correction can also be turned off manually under the Calibration menu by toggling the Cal Correction submenu key from On to Off. In that case, the display shows “CAL: OFF” for all traces that have valid correction data available.
When measuring with calibration Interpolation turned On, the calibration information data in the Instrument Settings Summary (item 1 in Figure: VNA Master Overview) shows “iCAL: ON (OK)”. This calibration setting information (including iCAL) is saved when a measurement is saved.
Note that “CAL: OFF” means that a calibration correction has been created, but it is not currently being used. This is different from “CAL: --”, which means that no valid calibration correction is available for the current setting.
When you have Cal Correction on, you cannot increase the frequency range or the number of points. You can, however, reduce the frequency range or decrease the number of points without forcing the calibration to become invalid. When reducing the frequency range, the VNA Master uses the appropriate points within the new frequency range that have correction coefficients applied to them. In that case, you can observe that the number of points that are being used for calibration correction are automatically reduced.
If you reduce only the number of points, then the frequency range is not changed. The VNA Master finds a subset of the original points in the sweep that can be used. You can therefore notice that the instrument may not use the exact number of points that you have entered. It picks a specific number of points that allow the calibration correction to continue to be valid. If you use the rotary knob, you will more easily find the available number of points that can be set. For example, if you calibrated with 201 points, then you can observe that you can reduce the number of points to 101, 68, 51, 41, and so forth.
If you change the source power setting, the calibration status is changed to “CAL: ON (?P)”, which indicates that source power has changed since the instrument was calibrated (from Low to High, or from High to Low). In this case, the calibration may still be valid, but a new calibration is recommended.
Another status information display that you may see is “CAL: ON (?T)” which indicates that the instrument temperature has deviated by more than a set amount since the time that the calibration was conducted. The calibration is most likely still valid, but a new calibration is recommended. If you see “CAL: ON (X)” on the display, then this indicates that the instrument temperature has deviated (since the time the calibration was conducted) by an amount that has more than likely rendered the calibration invalid. When this occurs, a new calibration is highly recommended before further measurements are conducted.
Only one calibration is available at a time. Performing a new calibration overwrites any existing calibration. You can, however, store a measurement setup (with CAL), which also stores the calibration. You can therefore have multiple calibrations available (as long as the calibration settings and conditions continue to apply).
Cal Type
The Cal Type submenu key is found in the Calibration Menu (shown in the VNA Measurement Guide). The Calibration Type list box provides the complete selection of available calibration types.
