Circulator vs Isolator
Both are non-reciprocal passive devices using ferrite magnetized by permanent magnets.
- Circulator (3-port): Signal travels only clockwise (or counter-clockwise). Port 1→2→3→1 with low loss, while 1→3 is blocked.
- Isolator (2-port): A circulator with port 3 terminated in 50 Ω. Signal passes port 1→2 (low loss) but blocked port 2→1 (high isolation).
Ideal Circulator S-Matrix (clockwise)
[0 0 1 ]
[S] = [1 0 0 ] (each entry represents S magnitude)
[0 1 0 ]
S21 = 1 (0 dB): port 1 → port 2, low loss
S32 = 1 (0 dB): port 2 → port 3, low loss
S13 = 1 (0 dB): port 3 → port 1, low loss
S31 = S12 = S23 = 0 (−∞ dB): counter-clockwise blocked
Typical Circulator/Isolator Specifications
| Parameter | Isolator Spec | Circulator Spec |
|---|---|---|
| Forward IL (S21) | <0.5 dB | <0.5 dB per path |
| Reverse isolation (S12) | >20 dB | >20 dB |
| Port match (S11, S22) | <−20 dB | <−20 dB |
| Frequency range | ±10–20% BW | ±10–20% BW |
| Max power | 10–500W typical | 10–500W typical |
Analysis in RF View
- Load circulator .s3p file → extract port pairs
- Forward path (ports 1→2): S21 → verify IL <0.5 dB
- Reverse path (ports 2→1): S21 of reversed .s2p → verify isolation >20 dB
- Port match: S11, S22, S33 → all <−20 dB
- For isolator: forward S21 and backward S12 → both in one .s2p file
RF View Circulator/Isolator: Load .s3p circulator file, extract clockwise path S21 and counter-clockwise path for isolation measurement. Compare forward vs reverse transmission on same chart. Free on Android.