Modification procedure

Calibration kit modification provides the capability to adapt to measurement calibrations in other con- nector types or to generate more precise error models from existing kits. Provided the appropri- ate standards are available, cal kit modification can be used to establish a reference plane in the same transmission media as the test devices and at a specified point, generally the point of device con- nection/insertion. After calibration, the resultant measurement system, including any adapters which would reduce system directivity, is fully cor- rected and the systematic measurement errors are mathematically removed. Additionally, the modifi- cation function allows the user to input more pre- cise physical definitions for the standards in a given cal kit. The process to modify or create a cal kit consists of the following steps:

1.Select standards

2.Define standards

3.Assign classes

4.Enter standards/classes

5.Verify performance

To further illustrate, an example waveguide cali- bration kit is developed as the general descriptions in MODIFY CAL KIT process are presented.

Select standards

Determine what standards are necessary for cali- bration and are available in the transmission media of the test devices.

Calibration standards are chosen based on the fol- lowing criteria:

•A well defined response which is mechanically repeatable and stable over typical ambient tem- peratures and conditions. The most common coaxial standards are zero-electrical-length short, shielded open and matched load termina- tions which ideally have fixed magnitude and broadband phase response. Since waveguide open circuits are generally not modelable, the types of standards typically used for waveguide calibration are a pair of offset shorts and a fixed or sliding load.

•A unique and distinct frequency response. To fully calibrate each test port (that is to provide the standards necessary for S11 or S22 1-PORT calibration), three standards are required that exhibit distinct phase and/or magnitude at each particular frequency within the calibration band. For example, in coax, a zero-length short and a perfect shielded open exhibit 180 degree phase separation while a matched load will pro- vide 40 to 50 dB magnitude separation from both the short and the open. In waveguide, a pair of offset shorts of correct length provide phase separation.

•Broadband frequency coverage. In broadband applications, it is often difficult to find stan- dards that exhibit a known, suitable response over the entire band. A set of frequency-banded standards of the same type can be selected in order to characterize the full measurement band.

•The TRL 2-PORT calibration requires only a sin- gle precision impedance standard—a transmis- sion line. An unknown high reflection device and a thru connection are sufficient to complete this technique.