Power Splitter Overview
A power splitter divides an input signal into two (or more) equal outputs. Key requirements are low insertion loss, good port match, and high isolation between output ports. The Wilkinson divider achieves all three simultaneously — a feat impossible with a simple resistive T-junction.
Wilkinson Divider Principle
The Wilkinson uses two λ/4 transmission line sections of impedance Z₁ = √2 · Z₀ (70.7 Ω in a 50 Ω system) plus an isolation resistor (100 Ω for equal split). S-parameters for an ideal equal-split Wilkinson:
| S-param | Magnitude | Phase | Meaning |
|---|---|---|---|
| S11 | 0 (−∞ dB) | — | Input perfectly matched |
| S21 = S31 | 1/√2 (−3.01 dB) | −90° | Equal split with 90° lag |
| S22 = S33 | 0 (−∞ dB) | — | Outputs matched |
| S23 = S32 | 0 (−∞ dB) | — | Outputs isolated |
Resistive Splitter Comparison
A simple resistive (delta or Y) splitter also provides 3 dB split but with fundamental differences:
| Parameter | Wilkinson | Resistive |
|---|---|---|
| Insertion loss | 3.01 dB (no resistive loss) | 6 dB (resistive loss) |
| Output isolation | >20 dB (with load) | 6 dB (inherent) |
| Bandwidth | Narrowband (λ/4 design) | DC to daylight |
| Port match | All ports matched | All ports matched |
| Use case | LO distribution, antenna feed | Test fixtures, wideband |
Analyzing a Splitter in RF View
Load the splitter's .s3p file and verify:
- S21 and S31: Should both be −3.0 ± 0.5 dB across the band
- Amplitude balance S21−S31: Should be <0.5 dB for good balance
- Phase balance: S21 phase − S31 phase should be <5° across band
- S11: Input return loss, should be <−20 dB
- S23: Output-to-output isolation, should be >20 dB
Broadband Wilkinson Designs
Single-section Wilkinson is narrowband (~10–15% bandwidth for <−20 dB return loss). Wideband designs use cascaded sections:
- 2-section: ~2:1 bandwidth ratio
- 3-section: ~4:1 bandwidth
- Exponential taper: Decade bandwidth but bulky
RF View's batch SNP processor lets you load swept-frequency .s3p files from multiple design iterations and overlay their S21/S31/S23 curves to compare bandwidth and balance.