China Electronics Technology Instruments AV3672 Series, User Manual

Page: 248 / 424

8 Basis of Network Measurement
8.1 Reflection Measurement
244
8 Basis of Network Measurement
This chapter introduces the following contents:
●
Reflection measurement
··························································································· 244
●
Phase measurement
································································································ 246
●
Amplifier parameter specifications
··············································································· 248
●
Complex impedance
······························································································· 251
●
Group delay
········································································································ 254
●
Absolute output power
···························································································· 257
●
AM-PM transformation
··························································································· 258
●
Linear phase deviation
····························································································· 260
●
Reverse isolation
··································································································· 262
●
Small signal gain and flatness
····················································································· 263
8.1 Reflection Measurement
Reflection measurement is an important part of network measurement. At first, the reflection measurement will be
introduced. In order to better understand reflection measurement, the optical wave is applied to simulate the
traveling wave transmission along the transmission line.
If any optical element such as the lens is set, part of light will be reflected by the lens, but the majority of light will
be transmitted continuously through the lens. If the surface of the optical element is a mirror, the majority of light
will be reflected, and only a little light will be transmitted or no light will be transmitted.
1. Incident light 2. Reflected light 3. Transmitted light
Fig. 8.1 Light Reflection and Transmission
The RF signal will be reflected if the impedance of two connectors is different from each other. Reflection
measurement is a process to measure the ratio of the reflected signal and incident signal. The incident signal is
measured by Receiver R, and the reflected signal is measured by Receiver A. Therefore, the result of reflection
measurement is a ratio of A and R (i.e. A/R). The reflection characteristic of the DUT can be fully quantified with
the signal amplitude and phase information of Receiver A and R. Among the S-parameter terms, S
11
represents the
reflection of Port 1 (input port) of the DUT and S
22
represents the reflection of Port 2 (input port) of the DUT.
Reflection measurement aims to ensure the efficient transmission of RF energy. If energy is reflected, only a little
energy will be transmitted to the expected place. In addition, if too much energy is reflected, the device may be
burnt, such as the output power amplifier.
●
Reflection measurement expression
·············································································· 244
●
Summary of reflection measurement expression
································································ 246
8.1.1 Reflection Measurement Expression
The data of reflection measurement can be expressed in various methods according to the requirements. Various
expressions are based on the same reflection measurement data and can be respectively displayed in one or more
graphic format(s). See details in “
4.7 Selection of Data Format and Scale
”.
8.1.1.1 Return Loss