Technical data

5-33
Operating Concepts
Measurement Calibration
termination at the measurement plane. All incident energy is absorbed. With S
11A
= 0 the equation can be
solved for E
DF
, the directivity term. In practice, of course, the "perfect load" is difficult to achieve, although
very good broadband loads are available in the compatible calibration kits.
Figure 5-28. "Perfect Load" Termination
Since the measured value for directivity is the vector sum of the actual directivity plus the actual reflection
coefficient of the "perfect load," any reflection from the termination represents an error. System effective
directivity becomes the actual reflection coefficient of the near "perfect load" as shown in Figure 5-29. In
general, any termination having a return loss value greater than the uncorrected system directivity reduces
reflection measurement uncertainty.
Figure 5-29. Measured Effective Directivity
Next, a short circuit termination whose response is known to a very high degree is used to establish
another condition as shown in Figure 5-30 on page 5-34.