Opening the Smith Chart in RF View
After loading any .s1p or .s2p (or larger) file in RF View, tap the Smith Chart display mode. By default, S11 is plotted. For a 2-port file, you can also display S22, the output impedance. The chart uses standard Z-normalized (50 Ω) coordinates unless you change the reference impedance in settings.
Reading Impedance Values
Tap any point on the Smith chart trace to display the impedance at that frequency:
- Center of chart = 50 Ω (perfect match, normalized Z = 1 + j0)
- Right edge = open circuit (Z = ∞)
- Left edge = short circuit (Z = 0)
- Upper half = inductive impedance (positive reactance)
- Lower half = capacitive impedance (negative reactance)
Common Smith Chart Patterns and Their Meaning
| Pattern | Component/Behavior |
|---|---|
| Small circle near center | Well-matched device across wide band |
| Arc clockwise along outer rim | Transmission line — moves toward source as frequency increases |
| Clockwise circle traversing center | Resonant circuit (antenna or filter resonance) |
| Large circle around top half | Inductive component dominant (spiral inductor) |
| Large circle around bottom half | Capacitive component dominant (bypass cap) |
Evaluating Matching Bandwidth
- Load the S11 file in RF View and view on Smith chart
- Observe how close the trace passes to the chart center (matched point)
- Use the −10 dB RL circle (displayed as a circle around the center) to identify the bandwidth
- Frequencies where the trace is inside the −10 dB circle = matched band
- Switch to rectangular S11 plot to read the exact −10 dB crossing frequencies
Filter Response on Smith Chart
A bandpass filter's S11 on the Smith chart shows:
- In the passband: trace near center (matched, energy transmitted)
- In the stopband: trace near outer rim (reflected, high S11)
- The trace sweeps around the chart as frequency increases through the stopband
- Each loop around the chart corresponds to a half-wavelength of the dominant mode
Matching Network Design with Smith Chart
To design a matching network from load Z_L to 50 Ω:
- Plot Z_L on Smith chart (the starting point)
- Adding a series inductor: move clockwise along constant-R circle
- Adding a shunt capacitor: move clockwise along constant-G circle
- Adding a transmission line section: rotate clockwise on constant-|Γ| circle
- Target: reach chart center (Z = 50 Ω)
RF View displays intermediate impedance points as you load component S-params in series, making the matching process visual and intuitive.
Exporting and Sharing Results
RF View lets you export Smith chart screenshots and S-parameter data via Android's share function. Export the .s2p file for further analysis in MATLAB or AWR Microwave Office. The standardized Touchstone format ensures compatibility across all major RF EDA tools.