RF Switch S-Parameter Overview
RF switches (SPDT, DPDT, SP4T, etc.) route RF signals between ports under electronic control. S-parameters differ significantly between ON state (signal path enabled) and OFF state (signal path disconnected). Both states must be characterized.
Key Switch S-Parameter Specifications
| Parameter | ON State | OFF State |
|---|---|---|
| Insertion Loss (S21) | −0.3 to −1.5 dB | N/A |
| Port Match S11, S22 | >15 dB RL | >15 dB RL |
| Port Isolation S21 | N/A | >30–50 dB |
| Frequency range | DC to 6 GHz typical | — |
SPDT Switch S-Parameter Measurement
For a single-pole double-throw (SPDT) switch with Port 1 = common, Port 2 = throw 1, Port 3 = throw 2:
State 1 (Port 1→2 ON, Port 3 OFF):
S21 = IL on path 1 (−0.5 dB at 2.4 GHz typical)
S31 = OFF-state isolation of path 2 (<−40 dB)
S11 = input port match (>15 dB RL)
State 2 (Port 1→3 ON, Port 2 OFF):
S31 = IL on path 2
S21 = OFF-state isolation of path 1
PIN Diode vs FET Switch Comparison
| Property | PIN Diode Switch | FET (CMOS/GaAs) Switch |
|---|---|---|
| Insertion Loss | 0.3–1.0 dB | 0.3–1.5 dB |
| Isolation (off) | 30–50 dB | 25–45 dB |
| Frequency range | DC–100 GHz | DC–6 GHz (CMOS), DC–100GHz (GaAs) |
| Power handling | High (1–100W) | Low–medium (<5W typical) |
| DC bias required | Yes (forward bias) | Gate voltage only |
RF View Switch Analysis: Load switch .s2p files for both ON and OFF states. Overlay them to visually compare IL vs isolation. Use multi-file overlay for different temperature or voltage bias conditions. Free on Android.