Power Divider Types and S-Parameter Characteristics
| Type | S21=S31 | S11 | S23 isolation | Best For |
|---|---|---|---|---|
| Wilkinson divider | −3 dB, 0° phase | <−20 dB | >20 dB | In-phase split, balanced amps |
| 90° hybrid (branch-line) | −3 dB, 90° phase | <−20 dB | >20 dB | IQ modulator, balanced mixer |
| Reactive T-junction | −3 dB, 0° phase | Poor (<−6 dB) | 0 dB (none) | Simple split, poor match |
| Rat-race (180° hybrid) | −3 dB, 0°/180° | <−20 dB | >20 dB | Mixer balun, difference port |
Wilkinson Divider Analysis Steps
- Load Wilkinson .s3p file
- Extract paths: Port1→Port2, Port1→Port3, Port2→Port3
- Check S21 = S31 = −3.0 ± 0.3 dB (equal power split)
- Check S11 < −20 dB at center frequency (matched input)
- Check S23 < −20 dB (Port 2 to Port 3 isolation)
- Phase: Phase(S21) − Phase(S31) = 0° ± 5° (in-phase split)
When Divider Performance Degrades
Bandwidth of Wilkinson divider: 20% fractional BW (±10% from f₀) Outside this BW: S11 rises, isolation drops, phase imbalance grows Common degradation: S23 drops below 20 dB: isolation resistor damaged or missing S21 ≠ S31 by >0.5 dB: asymmetric fabrication of λ/4 sections S11 poor: characteristic impedance of Z₁=70.7Ω lines not achieved
RF View Power Divider: Load .s3p file, extract all port pairs, overlay S21 and S31 for power balance check, use delta marker for phase balance, and single marker on S23 for isolation. Free on Android.