China Electronics Technology Instruments AV3672 Series, User Manual

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8 Basis of Network Measurement
8.9 Reverse Isolation
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b) If necessary, use the external attenuator or coupler to fully attenuate the output power of the amplifier and
prevent the receiver on Port 2 of the analyzer from compression or burning.
2) Select the S21 measurement mode.
3) Connect the DUT as shown in Fig. 8.21.
Fig. 8.21 Connection in Linear Phase Deviation Measurement
4) Select the analyzer settings corresponding to the DUT, including the phase format.
5) Remove and calibrate the DUT.
6) Reconnect the DUT and set the scale of measurement display to facilitate observation.
7) Change the electrical delay to make the phase trace flat.
8) Read the linear phase deviation through the marker.
9) Print or save the data.
8.9 Reverse Isolation
Reverse isolation aims to measure the reverse transmission response from the output to input of the amplifier.
8.9.1 What is reverse isolation?
The degree of isolation from the output end to input end of the device is measured in reverse isolation. Reverse
isolation measurement is similar to positive gain measurement, but with the following differences.
1) The stimulus signal is applied on the output port of the amplifier.
2) The response signal is measured at the input end of the amplifier.
3) The equivalent S-parameter is S12.
8.9.2 Why to measure reverse isolation?
The ideal amplifier should have infinite reverse isolation, and no signal is transmitted from the output end back to
the input end. Actually, the signal may be transmitted through the amplifier in the opposite direction. This kind of
unexpected reverse transmission may result in the interference of the reflected signal of the output port to the signal
transmitted forwards. Therefore, it is important to quantify reverse isolation.
8.9.3 Factors Related to Measurement Accuracy
As the amplifier generally has high loss in the reverse direction, the attenuator or coupler is not required to protect
the receiver of Port 1 in reverse transmission measurement. In case of no attenuator, the dynamic range and
measurement accuracy will be improved. The source power can be increased to improve the dynamic range and
accuracy.
Warning
The power must not be overloaded forward sweep or full double-port calibration.
With the attenuator eliminated and RF power increased, the receiver of Port 2 of the analyzer may be burnt in
forward sweep. Thus, forward sweep or full double-port calibration must not be done until the forward power is