#### Calibration Types

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) | S11 (or S22, ...) | Reflection tracking, Source match Directivity, | High | Reflection measurements on any port.
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, | High | 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 | All | Reflection tracking, Source match, Directivity, Load match, Transmission tracking | High, implicit verification | 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 | All | Reflection tracking, Source match, Directivity, Load match, Transmission tracking | High | 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, Line | All | Reflection tracking, Source match, Directivity, Load match, Transmission tracking | 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 | All | Reflection tracking, Source match, Directivity, Load match, Transmission tracking | 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.

##### Normalization

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.

##### Full One-Port Calibration

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.

##### One-Path Two-Port Calibration

A one-path two-port calibration combines a full one-port calibration
with a transmission normalization
, so it 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) and is suitable when only the forward (e.g. S11 and S21) or reverse S-parameters (e.g. S22 and S12) are to be measured and the DUT is well matched, especially at the load port.

##### TOSM Calibration

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 adapters 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.

##### TOM Calibration

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.

Implicit verification

The two one-port standards of the TOM A calibration type using three fully known standards (Through, Open, Match), recommended for 2-port measurements on coaxial systems. calibration are connected to both ports. Together with the four S-parameters of the through standard, this results in 8 S-parameter measurements.

Despite the fact that TOM uses fewer standards than TOSM A calibration type using four known standards (Through, Open, Short, Match), also called SOLT or 12-term error correction model. TOSM calibration is available for 2, 3 and 4-port measurements. – the short is missing –, the 3 fully known standards provide more information than necessary. This is due to the system error modeI that TOM and the other TXX calibration procedures (see below) are based on. This model has only 7 error terms in contrast to the TOSM model, which contains 10 terms.

The redundancy of TOM is used for an implicit verification of the solution. Implicit verification helps to detect and avoid calibration errors, e.g. errors due to defective cables or loose connections. In the case of failure of that implicit verification a warning message appears. The user may then continue or cancel the calibration.

##### TRM Calibration

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.

##### TRL Calibration

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. 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.

Frequency restrictions

The system of equations solved to derive the error terms is such that singularities occur whenever the length difference D L between the Through and the Line is equal to an integer multiple of half of the wave length:

As a rule, singularities are avoided with sufficient accuracy if the phase shift resulting from the length difference between through and line standard is between 20° and 160°. This corresponds to a ratio of 1:8 for the start and stop frequency of the calibrated sweep range.

To shift the calibrated sweep range to smaller or larger frequencies, you can use a longer or shorter line.

Example: Suppose you want to perform a TRL A calibration type using a Through and Line standard plus a possibly unknown Reflect standard. The calibration range is limited. Like TNA, TRL is especially useful for DUTs in planar line technology. calibration using coaxial air lines for the sweep range between 100 MHz and 4 GHz. The through standard has zero length. The ratio of the stop frequency to the start frequency is 40, therefore an accurate calibration with a single line standard is not possible. Proceed as follows:

1. Divide the sweep range into two subranges that meet the TRL calibration criterion, e.g. [100 MHz, 800 MHz] and [800 MHz, 4 GHz].

2. Determine the length L1 and L2 of the air lines from the following conditions in the center of the subranges:

L1 = l (450 MHz)/4 = 16.7 cm; L2 = l (2.4 GHz)/4 = 3.1 cm

3. Calibrate the subranges separately using the appropriate lines.

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.

##### TNA Calibration

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 zero 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.