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Making Measurements
Measuring Amplifiers
Measuring Gain and Reverse Isolation Simultaneously(ES Analyzers Only)
Since an amplifier will have high gain in the forward direction and high isolation in the
reverse direction, the gain (S21) will be much greater than the reverse isolation (S12).
Therefore, the power you apply to the input of the amplifier for the forward measurement
(S21) should be considerably lower than the power you apply to the output for the reverse
measurement (S12). By applying low power in the forward direction, you’ll prevent the
amplifier from being saturated. A higher power in the reverse direction keeps noise from
being a factor in the measurement and accounts for any losses caused by attenuators or
couplers on the amplifier’s output needed to lower the output power into the analyzer. The
following steps demonstrate the features that best accomplish these measurements.
1. Press .
Coupling the channels allows you to have the same frequency range and calibration
applied to channel 1 and channel 2.
2. Press .
Uncoupling the port power allows you to apply different power levels at each port. In
Figure 1-46, the port 1 power is set to −25 dBm for the gain measurement (S21) and the
port 2 power is set to 0 dBm for the reverse isolation measurement (S12).
3. Press and set the power level for
port 1.
4. Press and set the power level for
port 2.
5. Perform an error-correction and connect the amplifier to the network analyzer. Refer to
the Chapter 5 , “Optimizing Measurement Results,” for error-correction procedures.
6. Press .
You can view both measurements simultaneously by using the dual channel display
mode. Refer to Figure 1-46. If the port power levels are in different power ranges, one of
the displayed measurements will not be continually updated and the annotation tsH
will appear on the left side of the display. Refer to "Source Attenuator Switch
Protection" on page 7-13 for information on how to override this state.
NOTE To obtain best accuracy, you should set the power levels prior to performing
the calibration. However, the analyzer compensates for nominal power
changes you make during a measurement, so that the error correction still
remains quite valid. In these cases, the Cor annunciator will change to C∆.
Sweep Setup
COUPLED CH ON
Power
PORT POWER [UNCOUPLED]
Chan 1 Meas
Trans:FWD S21 ( B/R)
Power
Chan 2 Meas
Trans: REV S12 (A/R)
Power
Display
DUAL | QUAD SETUP
DUAL CHAN ON