Updated June 6,
here to go to our general discussion of Wilkinson power splitters
here to go to our main page on couplers and splitters
here to go to our page on the Lim-Eom three-way splitter
here to go to a page on the Kouzoujian N-way splitter
New for June 2010! Here's
an analysis of planar
New for August 2009!
Here's a page contributed by Paul Hubbard and Greg Ordy, on N-way,
unequal split Wilkinsons.
Here's an example contributed
by Kjer of a broadband eight-way
Here's an example contributed
by Limey Mark of a unique four-way splitter.
Wilkinson's original paper was on an N-way combiner, and it
is only fitting that we should deal with the subject of higher-order
Wilkinson splitters here.
For N-way combiners, the number
of arms is equal to N, while the number of ports is equal to N+1,
at least that is the convention we will maintain here.
Radial N-way Wilkinson combiners
Radial combiners are called that
because they have radial symmetry. Above N=2, the splitter cannot
be laid out in two dimensions.
For N=3 split, there are two
ways to realize the isolation resistors, the "star" and
A three-way Wilkinson is shown
below, with "star-resistor" configuration. The arms have
impedance SQRT(3)xZ0, and the resistors have impedance
Z0. By the way, the figures below, and many more, are
available in our download area
in a Word file, ElectronicSymbols.doc, for you to use in presentations
The next figure shows a three-way
Wilkinson with the "delta" resistor configuration. The
arms again have impedance SQRT(3)xZ0, but now the resistors
have impedance 3xZ0.
Now that we've looked
at the three-way Wilkinson, it is easy to guess what higher-order
Wilkinson combiner resistor networks look like. We'll give you a
hint... Every port has to be connected to every other port symmetrically.
The "delta" resistor pattern gets really ugly, so stick
with the star pattern for N=4 or higher.
Let's state the
rules for arm impedance and isolation resistors of N-way Wilkinson
combiners as a Microwaves101 rule of thumb:
For a basic N-way Wilkinson combiner, the arm impedance is SQRT(N)xZ0.
If you use star resistors, they are equal to Z0. If you
use delta resistors, they are equal to NxZ0.
Planar N-way Wilkinson combiners
In many instances, it is more
convenient to use a two-dimensional approximation of the radial
Wilkinson shown above. In this case, one of the resistors is deleted
from the layout, and a "fork" arrangement is the result.
here for an analysis of three types of three-way splitters,
in 50 ohms (very basic).
In the figure below, contributed
by Lou from Honeywell, a two-stage, three-way planar Wilkinson is
shown, along with its predicted responses (thanks, Lou!) Note to
readers: this is a very specialized splitter, it provides 12.5 ohm
impedance for the split ports and 50 ohms at the combined port.
What does this do
to performance? The primary thing that you give up is isolation
between the arms. Instead of greater than 20 dB, you might get 15
dB isolation. Also, there will be measurable differences between
the inside and outside arms.
from Limey Mark
Limey Mark is a good frend of
the Microwaves101 message board and cotributed this novel design
technique during October 2006. Thank you sir! Now in his own words...
It is possible to make a N-way
splitter on microstrip with no cross over. This technique has been
done at 100MHz. I would be interested to see if any one can do this
at a higher frequency.
Below you will see the image of a four-way splitter. This representation
was ‘knocked’ up in my garage with some old copper foil and a clapped
out Weller soldering iron so my apologies for the unprofessional
First of all this is not a multi layer board. This is a single layer
board the copper ground plane is visible in the photo. There is
a dielectric and another copper plane, which is where the track
has been etched and is the top of the board.
Look at the photo and for the time being ignore the air brush red
and yellow lines. What you see is the ground plane and four 2512
surface mount chip resistors soldered in a star point configuration,
the black air brush around the solder joints are the etching which
isolates it from the ground plane.
Now use your imagination and see an isolated via/post from the four
outer solder joints to the top of the board.
The yellow lines represent (though not to scale) the four 90 deg
100ohm lines, the red lines are the four 50 ohm lines which between
them intersect the four via’s.
Hey presto no cross over!
The board is placed on to a suitable recessed hole for the resistors.
Now obviously there will be issues at higher frequencies but I would
appreciate any feed back……good luck.