HP 85106D, Manual

Page: 69 / 244

2-24 HP 85106D mm-Wave System
Operation
1-Port Calibration
Figure 2-4 Phasor Diagram, Measuring Directivity Using Various Standards
Combining a fixed load with an offset load offers significantly better system
directivity. This “offset load” technique is a two-step process. First, the fixed
load is connected to the test port and measured. Then the same fixed load is
offset by the shim and measured again. Since the shim offsets the load by a
precisely known distance the angle of the resultant phase shift is known.
Using these two measurements and the angle the HP 8510C can determine
the exact directivity (Figure 2-4b). The accuracy of the offset load technique
depends on how precisely the offset delay is specified in the cal kit definition
(see section “Entering the Exact Offset Delay” on page 2-18).
A sliding load may also be used to determine directivity. The load element is
moved to five (or more) positions determining corresponding points of the
circle of Figure 2-4c. The HP 8510C then uses a circle-fitting routine to
determine the center of the circle which is the actual directivity. Again, the
effective directivity is determined by the dimensions of the line.
An important concern with the sliding load is the mechanical stability of the
load element. This restriction has made the sliding load technique
impractical in V and W bands, this is due to the small dimensions.
1-Port Reflection
Calibration Procedure
1. Begin the calibration procedure by pressing the following keys:
[
CAL
] then {
CAL KIT 1 WR-xx
}
{
CALIBRATE:S11 1-PORT
}
S
11
will automatically be displayed on the screen.
2. Connect the flush short and press {
SHORT
}.