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Operating Concepts
TRL*/LRM* Calibration (ES Models Only)
NOTE Dispersion Effects
Dispersion occurs when a transmission medium exhibits a variable propagation or phase
velocity as a function of frequency. The result of dispersion is a non-linear phase shift versus
frequency, which leads to a group delay which is not constant. Fortunately, the TRL
calibration technique accounts for dispersive effects of the test fixture up to the calibration
plane, provided that:
1. The thru (zero or non-zero length) is defined as having zero electrical length and is used
to set the reference plane (
).
2. The transmission lines used as calibration standards have identical dispersion
characteristics (i.e., identical height, width and relative dielectric constant).
When a non-zero length thru is used to set the reference plane, it should be defined as
having zero length in the TRL standards definition, even though it has physical length. The
actual electrical length of the thru standard must then be subtracted from the actual
electrical length of each line standard in the TRL calibration kit definition. The device must
then be mounted between two short lengths of transmission line so that each length is
exactly one-half of the length of the non-zero length thru standard. In this configuration, the
measurement will be properly calibrated up to the point of the device.
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