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Fig. 8.9 Phase Format of Analyzer
8.2.4.
Type of Phase Measurement
1) Complex impedance: the complex impedance data such as the resistance, reactance, amplitude and phase can be determined
by S11 and S22 measurement and observed in the Smith chart and polar coordinate format. See details in “8.4 Complex
Impedance".
2) AM-PM transformation: the unexpected phase offset may be caused by system amplitude changes in the AM-PM transformation
measurement, defined as the output phase change of each 1dB increase of the power input into the amplifier, in degree/dB.
Measurement is done at the 1dB gain compression point. See details in “8.7 AM- PM Transformation".
3) Linear phase offset: refer to the phase distortion produced in measurement of the tested device. Ideally, the phase shift of the
tested device is linear to the frequency. The deviation produced relative to the theoretical phase offset is referred to as the linear
phase offset (also known as the phase linearity). See details in “8.9 Linear phase offset".
4) Group delay: it is another way to measure the phase distortion of the device. The transition time of the signal of specific
frequency through the device is measured, and the group delay is calculated according to the derivative of the measured phase
response. See details in “8.5 Group Delay".
8.2.5.
Linear phase offset and Group Delay
The linear phase offset and group delay are phase information of the measurement device but for different purposes.
1) Advantages of linear phase offset measurement:
a) The noise is lower than that of group delay measurement.
b) The characteristics of the device transmitting phase-modulated signals can be better represented. In this case, it is more
appropriate to use the phase as the unit instead of the second.
2) Advantages of group delay measurement:
a) Compared with the linear phase offset measurement, phase distortion can be explained more easily.
b) The characteristics of the tested device can be represented accurately. The phase ripple slope is calculated by the analyzer
in group delay measurement and depends on the ripple quantity within the unit frequency. Phase responses with the same
phase ripple peak-peak value are compared. Large phase slope response may result in large group delay changes and
signal distortion.
8.3.
Amplifier Parameter Specifications
This section introduces the measurement parameters of the amplifier.
8.3.1.
Gain
The gain refers to the ratio between the output power (to the characteristic impedance load) and input power (from the characteristic
impedance source) of the amplifier and can be calculated by the following formula.
