The analyzer provides a wide range of calibration types for one, two or more ports. The calibration types differ in the number and types of standards used, the error terms, i.e. the type of systematic errors corrected and the general accuracy. The following table gives an overview.
Calibration Type
Standards
Parameters
Error Terms
General Accuracy
Application
Reflection Normalization
Open or Short
S11 (or S22, ...)
Reflection tracking
Low to medium
Reflection measurements on any port.
Transmission Normalization
Through
S12, S21 (or S13,...)
Transmission tracking
Medium
Transmission measurements in any direction and between any combination of ports.
Full One-Port
Open, Short, Match1)
Reflection tracking, Source match Directivity,
High
One-Path Two-Port
Open, Short, Match1) (at source port), Through2)
S11, S21 (or S22,...)
Reflection tracking, Source match, Directivity, Transmission tracking
Medium to high
Unidirectional transmission measurements in any direction and between any combination of ports.
TOSM (2-port, 3-port or 4-port) or UOSM
Open, Short, Match1) (at each port), Through2) (between all combinations of 2 ports)
All
Reflection tracking, Source match, Directivity, Load match, Transmission tracking,
Reflection and transmission measurements on DUTs with 2, 3, or 4 ports; classical 12-term error correction model.
TOM (2-port, 3-port or 4-port)
Open, Match (at both ports), Through
Reflection tracking, Source match, Directivity, Load match, Transmission tracking
Reflection and transmission measurements on DUTs with 2, 3, or 4 ports.
TRM (2-port, 3-port or 4-port)
Reflect (equal at both ports), Match, Through
Reflection and transmission measurements on DUTs with 2, 3, or 4 ports, especially in test fixtures.
TRL (2-port, 3-port or 4-port)
Reflect (at both ports), Through, Line1, Line2/3 (optional), combination with TRM (optional)
High, high directivity
Reflection and transmission measurements on DUTs with 2, 3, or 4 ports, especially for planar circuits. Limited bandwidth.
TNA (2-port, 3-port or 4-port)
Through, Attenuation, Symmetric network
High, lowest requirements on standards
Reflection and transmission measurements on DUTs with 2, 3, or 4 ports, especially for planar circuits.
1) Or any other 3 known one-port standards. To be used in a guided calibration, the known standards must be declared to be open, short, and match irrespective of their properties; see Add/Modify Standard dialog.
2) Or any other known two-port standard. See remark above.
The calibration type must be selected in accordance with the test setup. Select the calibration type for which you can obtain or design the most accurate standards and for which you can measure the required parameters with best accuracy.
A normalization is the simplest calibration type since it requires the measurement of only one standard for each calibrated S-parameter:
One-port (reflection) S-parameters (S11, S22, ...) are calibrated with an open or a short standard providing the reflection tracking error term.
Two-port (transmission) S-parameters (S12, S21, ...) are calibrated with a through standard providing the transmission tracking error term.
Normalization means that the measured S-parameter at each sweep point is divided by the corresponding S-parameter of the standard. A normalization eliminates the frequency-dependent attenuation and phase shift in the measurement path (reflection or transmission tracking error). It does not compensate for directivity or mismatch errors. This limits the accuracy of a normalization.
A full one-port calibration requires a short, an open and a match standard to be connected to a single test port. The three standard measurements are used to derive all three reflection error terms:
The short and open standards are used to derive the source match and the reflection tracking error terms.
The match standard is used to derive the directivity error.
A full one-port calibration is more accurate than a normalization but is only applicable for reflection measurements.
A one-path two-port calibration combines a full one-port calibration with a transmission normalization. The fully calibrated port is termed the node port. This calibration type requires a short, an open and a match standard to be connected to a single test port plus a through standard between this calibrated source port and a second load port. The four standard measurements are used to derive the following error terms:
The short and open standards are used to derive the source match and the reflection tracking error terms at the source port.
The match standard is used to derive the directivity error at the source port.
The through standard provides the transmission tracking error term.
A one-path two-port calibration requires only four standards to be connected (instead of 7 for a full two-port TOSM calibration). It is suitable when only the forward (e.g. S11 and S21) or reverse S-parameters (e.g. S22 and S12) are needed, and if the DUT is well matched, especially at the load port.
A TOSM (Through – Open – Short – Match) calibration requires the same standards as the one-path two-port calibration, however, all measurements are performed in the forward and reverse direction. TOSM is also referred to as SOLT (Short – Open – Load = Match – Through) calibration. The four standards are used to derive 6 error terms for each signal direction:
In addition to the source match and reflection tracking error terms provided by the one-path two-port calibration, TOSM also provides the load match.
The directivity error is determined at both source ports.
The transmission tracking is determined for each direction.
TOSM calibration is provided for 2-port, 3-port or 4-port measurements. The number of required standard measurements and of error terms increases as shown in the following table.
Number of ports
Number of standards to be connected
Number of standard measurements
Number of error terms
2
2 * 3 +1 = 7
2 * 3 +2 * 1 = 8
2 * 3 + 2 * 2 = 10
3
3 * 3 + 2 + 1 = 12
3 * 3 +2 * (2 + 1) = 15
3 * 3 + 2 * 2 * 3 = 21
4
4 * 3 +3 + 2 + 1 = 18
4 * 3 +2 * (3 + 2 + 1) = 24
4 * 3 + 2 * 2 * 6 = 36
An open, through and match measurement is required at each port; in addition, a through must be measured between any combination of ports and in both directions. Therefore the number N of standard measurements for an n-port TOSM calibration is equal to
The analyzer automatically performs each through measurement in both directions, so the number of connected standards is smaller than the number of measurements.
TOSM with unknown Through, UOSM
The network analyzer supports different connector types at its test ports in order to measure DUTs with different port connectors. To perform a TOSM calibration, the DUT must be replaced by a through connection, which generally involves an adapter between the two connector types.
An adapter represents a through standard with unknown characteristics (in particular, with unknown delay time/transmission phase). The analyzer can perform a TOSM calibration with an unknown through, provided that it is reciprocal (S21 = S12). The modified TOSM calibration is referred to as UOSM (Unknown through – Open – Short – Match) calibration. It can be selected as follows:
If different connector types are assigned to the test ports, the analyzer automatically replaces TOSM –> UOSM.
If the same connector types are used but the appropriate through standard is not defined, the analyzer also replaces TOSM –> UOSM.
UOSM can be selected explicitly using Channel –Calibration –Start Cal –Other....
After acquiring the calibration sweep data for the unknown through, the analyzer automatically determines its delay time/transmission phase; see Unknown Through Standard.
UOSM calibration is not compatible with segmented frequency sweeps.
A TOM (Through – Open – Match) calibration requires a low-reflection, low-loss through standard with an electrical length that may be different from zero, an open, and a match. The characteristics of all standards must be fully known; the match may have non-ideal characteristics.
A TRM (Through – Reflect – Match) calibration requires a low-reflection, low-loss through standard with an electrical length that may be different from zero, a reflect, and a match. The magnitude of the reflection coefficient of the reflect standard can be unknown but must be nonzero; its phase must be roughly known (90 deg). The magnitude and phase of the reflection coefficient must be the same at both test ports.
TRM calibration is especially useful for DUTs in test fixtures.
A TRL (Through – Reflect – Line) calibration requires the two-port standards through and line, which are both assumed to be ideally matched. Beyond that, the through must be lossless, and its length must be exactly known. The length of the line standard must be known approximately.
Furthermore, a reflecting one-port standard (reflect) is needed. The magnitude of the reflection coefficient of the reflect standard can be unknown but must be nonzero; its phase must be roughly known (90 deg). The magnitude and phase of the reflection coefficient must be the same at both test ports.
TRL calibration is especially useful for DUTs in planar line technology (e.g. test fixtures, on-wafer measurements) where it is difficult to design and connect accurately modeled open, short or match standards. If TRL is not practicable, TNA may be an alternative.
The system of equations solved to derive the error terms is such that singularities occur whenever the length difference ΔL between the through and the line is an integer multiple of half of the wave length: Refer to TRL Extensions to learn how to avoid singularities (extension with two lines, combination with TRM).
A TNA (Through – Network – Attenuation) calibration requires two-port standards only. Again, the through standard must be ideally matched and lossless. The symmetric network must have the same properties as the reflect standard used for a TRL calibration, i.e. the magnitude of its reflection coefficient can be unknown but must be nonzero; its phase must be roughly known (90 deg). The magnitude and phase of the reflection coefficient must be the same at both test ports. The attenuation standard must be well matched on both sides and cause an attenuation different from 0 dB; the exact value of the transmission coefficient is not important.
As with TRL, TNA calibration is especially useful for planar DUTs. If TNA is not practicable, TRL may be an alternative.