China Electronics Technology Instruments AV3672 Series, User Manual

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8 Basis of Network Measurement
8.10 Small Signal Gain and Flatness
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low enough, which cannot result in burning of the receiver of Port 2 of the analyzer.
If the tested amplifier is highly isolated, the level of the reverse signal may be close to the base noise or crosstalk
level of the receiver. In order to reduce the base noise, the averaging function can be applied. The dynamic range
and accuracy of measurement can be improved by increasing the averaging times or reducing the intermediate
frequency bandwidth, at the sacrifice of measurement velocity.
1) If the measurement accuracy is affected by the crosstalk, the through type response and isolation calibration can
be implemented to reduce crosstalk errors. Use the same average factor and intermediate frequency bandwidth
during calibration and measurement.
2) The frequency response of the test is a main error source in reverse isolation measurement. It can be eliminated
by through type response or through type response/isolation calibration.
3) If the temperature varies, the amplifier response may be thoroughly difference. The test should be done at the
working temperature of the amplifier.
8.9.4 Steps of Reverse Isolation Measurement
1) Reset the analyzer.
2) Select the S12 measurement type.
3) Connect the amplifier as shown in Fig. 8.22 and provide the DC bias.
Fig. 8.22 Connection in Reverse Isolation Measurement
4) Set the analyzer corresponding to the tested amplifier.
5) Remove and calibrate the amplifier and perform through type response calibration or through type
response/isolation calibration.
6) Reconnect the amplifier and set the scale of measurement display to facilitate observation.
7) Read the reverse isolation value at the corresponding frequency point through the marker.
8) Print or save the data.
8.10 Small Signal Gain and Flatness
The small signal gain refers to the gain of the amplifier within the linear working zone. Generally, it is measured at
the constant input power within the frequency sweep range. The gain flatness refers to the gain change within the
specified frequency range.
8.10.1 What is gain?
The amplifier gain is defined as the power difference between the output signal and input signal of the amplifier
(power unit: dBm), given that the input impedance of the amplifier is the same as the output impedance. It is the
characteristic impedance of the system.
1) The gain is referred to as S21 among the S-parameter terms.
2) The gain is expressed as the logarithmic ratio of the output power and input power (dB).