Gysel power splitter

Updated April 9, 2005

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Ulrich Gysel published a IEEE paper titled "A New N-way Power Divider/Combiner Suitable for High-Power Applications" around 1975(?). His solution looks like a cross between a branchline and a Wilkinson. It provides in-phase outputs, is configured most commonly as a two-port but can serve as an N-way splitter as well. We will describe a two-way Gysel here.

Gysel didn't provide closed-form equations for his splitter, he used a CAD program to optimize the line impedances. That's what we did when we designed one. We didn't use the transformer Z₁ (let it be 50 ohms). The other three impedance work out to be:

Z₂=70.35 ohms

Z₃=50 ohms

Z₄=25 ohms (other values are possible, it affects the bandwidth).

The big advantage of the Gysel power splitter is its power handling. In a Wilkinson splitter, the resistor is embedded into the network, and must provide a short phase length for the scheme to work. The terminations in a Gysel are equal to Z₀, and can be high-power loads if power handling is a requirement (such as in a transmitter). The loads can be external to the power splitter, any length of Z₀ transmission line can be added between the loads and the splitter.

Etched onto a thin-film, there is no way to measure the resistor in a Wilkinson, because it is shorted out by the transmission lines around it. The Gysel allows the two resistors to be measured in parallel, even if they are grounded to the substrate.

Below is a plot of the insertion loss from input to the two output ports. The one dB bandwidth is a remarkable 61.8%, which is more than double the bandwidth of a simple branchline power splitter.

The final plot shows the return loss at port 1, as well as the isolation between ports 2 and 3. The return loss bandwidth for 1.5:1 VSWR (-14 dB return loss) is 44.4%. This again beats the simple branchline which provides 20.8% bandwidth at 1.5:1 VSWR.