Click here to go to our general discussion of Wilkinson power power dividers
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 "RW" is the Wilkinson isolation resistor). The math for computing the line impedances in the figure below is provided on this page.
Topology for unequal-split Wilkinson
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:
- All ports are perfectly matched at center frequency
- Infinite isolation is achieve at center frequency
- In the even mode (exciting Port 1) the splitter is lossless.
When you look at any of the unequal-Wilkinson solutions, keep an eye on these three properties!
What about N-way unequal splits? We offer two ways to do that. The direct way is located here. You can probably figure out a way to make unequal splits of any N-value (3,4,5,6,7...) by cascading two-way and three-way Wilkinsons; this is often done in antenna feed networks for tapered apertures. Maybe we will cover that later...