How it works
A two-way Wilkinson divider uses two quarter-wave lines of √2 × Z₀, about 70.7 Ω in a 50 Ω system, from the input to each output, with a resistor of 2 × Z₀ between the outputs. At the design frequency, all three ports are matched, the outputs get equal power in phase, and they're isolated from each other, so a fault or mismatch on one doesn't upset the other. 75 Ω coax is close enough to 70.7 Ω for most amateur use.
Variations
- Lumped version: at HF and low VHF, where quarter-wave lines are long, each line can be replaced by an inductor with a capacitor to ground at each end.
- N-way: N lines of √N × Z₀ with a resistor of Z₀ from each output to a common point.
- Unequal split: different line impedances send more power to one port. The outputs then need matching sections to bring them back to Z₀.
The bandwidth is roughly 20 to 40% of the centre frequency for a single section. For a coax harness without the resistor, which is simpler for feeding two antennas, see the Yagi stacking calculator.
Questions
What line impedance does a 50 Ω Wilkinson need?
70.7 Ω, √2 × 50. 75 Ω coax works well in practice.
What resistor value is used?
100 Ω, twice the system impedance, between the two outputs.
How much loss is in each output?
3 dB for a two-way split, because the power is shared, plus a few tenths of a dB of real loss.
Can a Wilkinson combine two amplifiers?
Yes. Used in reverse, it combines two equal, in-phase signals, and the resistor absorbs any imbalance.