Quick Start: Learning How to Make Measurements
Learning to Make Reflection Measurements
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 (G) uniquely defines a device impedance; G = 0 only occurs when the device and analyzer impedance are exactly the same. The reflection coefficient for a short circuit is: G = 1 Ð 180°. Every other value for G also corresponds uniquely to a complex device impedance, according to the equation:
ZL = [(1 + G) / (1
where ZL is your test device impedance and Z0 is the measuring system's characteristic impedance (usually 50W or 75W).
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.
•Choose LIN MKR if you want the analyzer to show the linear magnitude and the phase of the reflection coefficient at the marker.
•Choose LOG MKR if you want the analyzer to show the logarithmic magnitude and the phase of the reflection coefficient at the active marker. This is useful as a fast method of obtaining a reading of the log magnitude value without changing to log magnitude format.
•Choose Re/Im MKR if you want the analyzer to show the values of the reflection coefficient at the marker as a real and imaginary pair.
• Choose R+ jX MKR (the default marker format) to show the real and imaginary parts of the device impedance at the marker. Also shown is the equivalent series inductance or capacitance (the series resistance and reactance, in ohms).
Chapter 2 |