Calibration Standards
This following section explains the general principles and terms regarding calibration kit files. To learn how to modify calibration kit files, See Modify Calibration Kits.
A calibration kit contains a set of physical devices called standards. Each standard has a precisely known or predictable magnitude and phase response as a function of frequency. All Keysight Cal Kits and their standard definitions are stored in the analyzer. For a list of Keysight calibration kits, see Analyzer Accessories.
Calibration standards provide the reference for error-corrected measurements in the network analyzer. Each standard has a precisely known definition that includes electrical delay, impedance, and loss. The analyzer stores these definitions and uses them to calculate error correction terms.
During measurement calibration, the analyzer measures standards and mathematically compares the results with the definitions ("ideal models") of those standards. The differences are separated into error terms that are later removed from device measurements during error correction. See Systematic Errors.
A standard type is one of four basic types that define the form or structure of the model to be used with that standard. The following are the four basic standard types:
Standard |
Terminal Impedance |
|
SHORT |
zero ohms |
|
OPEN |
infinite ohms |
|
LOAD |
system impedance, Z0 |
|
THRU/LINE |
no terminal impedance |
Learn about other Calibration Standards:
Standard definitions describe the electrical characteristics of the standards and the frequencies they will be used. Standard definitions can be viewed from the Advanced Modify Cal Kit menu selection. Standard definitions include:
-
Minimum Frequency Specifies the minimum frequency the standard is used for calibration.
-
Maximum Frequency Specifies the maximum frequency the standard is used for calibration.
-
Z0 Specifies the characteristic impedance of the standard (not the system characteristic impedance or the terminal impedance of the standard).
-
Delay Specifies a uniform length of transmission line between the standard being defined and the actual calibration plane.
-
Type Specifies type of standard (SHORT, OPEN, THRU/LINE, LOAD, ARBITRARY).
-
Loss Specifies energy loss, due to skin effect, along a one-way length of coaxial cable.
Loss model equation:
-
The value of loss is entered as ohms/second at 1 GHz.
-
To compute the loss of the standard, measure the delay in seconds and the loss in dB at 1 GHz. Then use the following formula:
Capacitance model equation:
C0, C1, C2, C3. Specifies the fringing capacitance for the open standard.
-
C = (C0) + (C1 x F) + (C2 x F²) + (C3 x F³)
-
(F is the measurement frequency).
-
The terms in the equation are defined when specifying the open as follows:
-
-
C0 term is the constant term of the third-order polynomial and is expressed in Farads.
-
C1 term is expressed in F/Hz (Farads/Hz).
-
C2 term is expressed in F/Hz².
-
C3 term is expressed in F/Hz³.
-
Inductance model equation:
L0, L1, L2, L3. Specifies the residual inductance for the short standard.
-
L = (L0) + (L1 x F) + (L2 x F²) + (L3 x F³)
-
(F is the measurement frequency).
-
The terms in the equation are defined when specifying the short as follows:
-
-
L0 term is the constant term of the third-order polynomial and is expressed in Henries.
-
L1 term is expressed in H/Hz (Henries/Hz)
-
L2 term is expressed in H/Hz².
-
L3 term is expressed in H/Hz³.
-
Once a standard is characterized, it must be assigned to a standard "class". A standard class is a group of standards that are organized according to the calibration of the network analyzer error model.
The number of classes needed for a particular calibration type is equal to the number of error terms being corrected.
A class often consists of a single standard, but may be composed of multiple standards. These may be required for accuracy or to cover a wide frequency range.
Example: A response calibration requires only one class, and the standards for that class may include an OPEN, or SHORT, or THRU. A 1-port calibration requires three classes. A 2-port calibration requires 10 classes, not including two for isolation.
The number of standards assigned to a given class may vary from one to seven for unguided calibrations. Guided calibrations allow as many standards as needed.
Calibration Classes are assigned in the Advanced Modify Cal Kit menu, SOLT or TRL tab.
The different classes used in the analyzer
S11A, S11B, S11C (S22A, S22B, S22C and so forth)
These are the three classes for port 1-reflection calibrations (three classes also for S22 and S33). They are used in the one-port calibrations and the full two-port calibration. They are required in removing the directivity, source match, and reflection tracking errors. Typically, these classes might consist of an open, a short and a load standard for each port.
Transmission and Match (forward and reverse)
These classes are used to perform a full two-port calibration. The transmission class relates primarily to the transmission tracking, while the match class refers to load match. For both of these classes, the typical standard is a thru or delay.
Isolation
The isolation classes are used to perform a full two-port and the TRL two-port calibrations. The isolation classes apply to the forward and reverse crosstalk terms in the network analyzer error model.
TRL THRU
These are used to perform a TRL two-port calibration. The TRL thru class should contain a thru standard or a short line. If it contains a non-zero length thru standard, then the calibration type is called LRL or LRM.
TRL REFLECT
This class is used to perform a TRL two-port calibration. The TRL reflect class should contain a standard with a high reflection coefficient, typically an open or short. The actual reflection coefficient need not be known, but its phase angle should be specified approximately correctly (± 90 deg). The exact same reflection standard must be used on both ports in the TRL calibration process.
TRL LINE or MATCH
These are used to perform a TRL two-port calibration. The TRL line or match class should contain line standards, load standards, or both. If a line standard is used, its phase shift must differ from that of the TRL THRU standard by 20° to 160°. This limits the useable frequency range to about 8 to 1. Two or more line standards of different lengths may be specified to get broader frequency coverage. It is also common to include a load standard for covering low frequencies, where the line's length would be impractically long. When a load is used, the calibration type is called TRM or LRM.
Note: For more information, read Specifying Calibration Standards and Kits for Keysight Vector Network Analyzers (Application Note 1287-11)