How to set up a cal kit with microstrip line standards.
Agilent network analyzers offer two models for the transmission
medium - coax or waveguide.
They do not include a model for microstrip dispersion, where the
electrical delay of a line varies with frequency.
If your calibration standards are in microstrip, you have to choose the
coax model, and use average values for the electrical delays of your
In the case of a TRL calibration, you do not need to know the
precise delay of the line standard; this value is determined as part
of the calibration process.
So you can specify an approximate value of delay from the center of
your frequency range; it need only be accurate to +/- 1/4
wavelength or +/- 90 degrees over the entire range.
In the case of a LRL calibration (non-zero length thru standard),
you can specify the thru standard to have zero length in the cal kit
definition, so that the reference planes are established in the middle
of the thru.
For the line standard's delay, enter the delay difference
between it and the thru standard.
Then your device or fixture should be mounted between two lines that
are each exactly one-half the length of the thru standard.
This approach is often used to make a calibrated measurement of a
transistor or RFIC mounted on a PC board.
By moving the calibration reference planes to the middle of the thru
standard, you can remove the errors of the PCB connectors and traces.
An SOLT calibration in microstrip is probably not a great idea,
unless you have a narrow frequency range and can ignore dispersion.
If you do have a wider frequency range, you should break it up into
several smaller bands.
For any cal standard that includes a length of microstrip line, you
will need to define several standards in the cal kit definition, one
for each frequency band.
Then approximate the dispersive delay with a different constant
value for each band.