Unequal-split Wilkinsons

Revised August 13, 2011

Click here to go to our general discussion of Wilkinson power splitters

Click here to go to our unequal-split power divider calculator, it handles Wilkinsons, rat-races and branchline couplers!

Our material on unequal-split Wilkinsons is spread onto the following pages:

Split Tee Power Divider - the original unequal Wilkinson splitter from 1965

Unequal split Wilkinsons, the rest of the story (Microwaves101 exclusive, from 2009!)

Maximally-flat transformers used in unequal split Wilkinsons

Kouzoujian's N-way splitter - uses unequal splitters in a planar layout (Microwaves101 exclusive!)

Traveling wave combiner (mostly used to create equal outputs but unequal math is required)

N-way, unequal split Wilkinsons - by Paul Hubbard and Greg Ordy of Seed Solutions (Microwaves101 exclusive!)

Our page on the rest of the story on unequal-split Wilkinsons derives the math behind the impedance calculations. We'll show you an extra degree of freedom that the classic unequal-split Wilkinson equations don't provide.

We are talking about two-way Wilkinson splitters here, but of course you can make unequal split N-way dividers. The way to make power split unequally requires two things: the quarterwave sections must be of different impedance, to encourage more of the signal to travel in/out the lower-impedance arm, and a second set of quarter-wave sections are needed, to transform the arm impedances back to 50 ohms. The structure looks similar to a two-stage Wilkinson without the second isolation resistor (here "R_W" is the Wilkinson isolation resistor).

The above image and many more are available in a Word document you can get in our download area (for free).

What constitutes a valid solution to the unequal splitter network? There are really just three criteria that must be met:

1. All ports are perfectly matched at center frequency
2. Infinite isolation is achieve at center frequency
3. In the even mode (exciting Port 1) the splitter is lossless.