General Operating Information
2
Keysight U2040 X-Series User’s Guide
69
Gamma correction
Figure 2-14
DUT to U2040 X-Series connection diagram
In a realistic measurement environment, the Device-Under-Test (DUT) impedance or the
reference impedance (Z
o
) is not equal to the U2040 X-Series impedance. The mismatch in
impedance values causes a portion of the signal voltage to be reflected. This is quantified
by the reflection coefficient, or gamma (
Γ
). A portion of the incident power to the
U2040 X-Series, P
i
, is reflected back to the DUT as P
r
. The remaining power, P
d
, gets
delivered to the U2040 X-Series. A generic DUT will reflect part of P
r
back to the
U2040 X-Series, and the reflected portion will be superimposed onto P
i
. The nominal
power, P
zo
— the power generated after factoring in Z
o
— may be calculated as follows:
Gamma correction compensates for impedance mismatch via two options, which are Single
Point Gamma and Table-based Gamma.
Single Point Gamma
Single Point Gamma correction is used when you have a known and constant frequency, so
a single gamma value can be used for calculation. The value for
Γ
DUT
may be entered as a
Single Point Gamma which may be applied across all measurement frequencies in the
U2040 X-Series operating range.
Table-based Gamma
Table-based Gamma is used when there are multiple known frequencies, leading to
multiple gamma values. This option supports a list of up to 1024 measurement frequency
values.
U2040 X-Series
DUT
Γ
DUT
Γ
L
P
r
P
i
P
d
P
zo
P
i
1
Γ
DUT
Γ
L
–
2
=