Upconverter Settings
R&S
®
SGU100A
81
User Manual 1176.7726.02 ─ 09
Figure 7-2: Negative gain imbalance (left) and positive (right) gain imbalance in the I/Q constellation
diagram
7.3.1.2
I and Q Offset
An I offset adds a constant value to all I amplitudes, leaving the Q amplitudes
unchanged. A Q offset has the opposite effect. A combination of I and Q values results
in an I/Q offset, which is usually due to carrier feedthrough in the I/Q modulator. Possi-
ble reasons are interfering signals at the RF carrier frequency, e.g. an unsuppressed
RF carrier subchannel. The effect of a positive I and Q offset in the I/Q constellation
diagram is shown below.
Figure 7-3: I offset (left) and Q offset (right) in the I/Q constellation diagram
7.3.1.3
Quadrature Offset
Changes the phase angle between the I and Q vectors from the ideal 90 degrees,
while the amplitudes are maintained. A positive quadrature offset results in a phase
angle greater than 90 degrees. The effect of a positive quadrature offset in the I/Q con-
stellation diagram is shown below.
I/Q Modulation and Signal Impairment