Quick Start: Learning How to Make Measurements
Learning to Make Reflection Measurements
Figure 2-14 Example S11 or Reflection Measurement Trace in Polar Format
Measuring S11 and S22 or Reflection in a Smith Chart Format.
• Measuring Impedance
The amount of power reflected from a device is directly related to the impedance of the device and the measuring system. Each value of the reflection coefficient (Γ) uniquely defines a device impedance; Γ = 0 only occurs when the device and analyzer impedance are exactly the same. The reflection coefficient for a short circuit is: Γ = 1 ∠ 180°. Every other value for Γ also corresponds uniquely to a complex device impedance, according to the equation:
ZL = [(1 + Γ) / (1 −Γ)] × Z0
where ZL is your test device impedance and Z0 is the measuring system's characteristic impedance (usually 50Ω or 75Ω).
1.Press 
Format
SMITH CHART 
Scale Ref
AUTO SCALE .
2. Press 
Marker Fctn
MARKER MODE MENU SMITH MKR MENU and turn the front panel knob to read the resistive and reactive components of the complex impedance at any point along the trace, as shown in Figure
The marker annotation also gives the series inductance or capacitance (132.87 pF in this example). The complex impedance is capacitive in the bottom half of the Smith chart display and is inductive in the top half of the display.
Chapter 2 |
