# Compact Wilkinson Example 2: the Scardelletti power divider

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New for August 2024.  We split the content below from this page which was getting too long.  Now each compact Wilkinson has its own page:

Example 1: Webb power divider

Example 2: Scardelletti power divider

Example 3: Kang power dividers

The Scardelletti divider was pointed out to us by Microwaves101 knifewinner Emily. It was described in an January 2002 IEEE article entitled Miniaturized Wilkinson Power Dividers using Capacitive Loading, by Scardelletti et al.

The technique used is to increase the line impedance of the arms, while loading the structure with capacitors C1 at the split ports and C2 at the common port (C2=2xC1). This is actually a pretty basic concept that we will eventually describe in our page on quarterwave tricks. Here' s a schematic we generated in Eagleware's Genesys (once again we ignored proper capacitor designators!)

In the referenced paper, equations are given for line impedance as a function of electrical length. Guess what? There's a mistake in the equation given for capacitance! The authors submitted a correction which you can see here. What it comes down to is the capacitance at the common node needs to be twice the capacitance one the split nodes.

Update May 2024... We propagated that mistake on this site, which was noticed by Armando (thanks!) It's time to make amends. Let's step back and look at the schematic from the original paper.

Below is Arturo's corrected equations.  Note that in his country, they don't say "sine, cosine and tangent", they speak of "seno, coseno y tangento". This is a multi-cultural website, and that is your Spanish lesson for today!  Arturo's equations use frequency in radians per second, and capacitance in Farads.

We created a Microwave Office project for this circuit, you will find it in our download area.  Our version of the equations (shown below) express the frequency in GHz and capacitance in picoFarads.

The plot below shows the line impedances and shunt capacitor value as functions of line length in degrees, for this type of splitter in a fifty ohm system. When the line length is 90 degrees, the design reverts to a conventional Wilkinson coupler, with impedances 70.7 ohms and capacitors at zero value. The capacitor values given are for 1 GHz center frequency, if you want to scale them to other frequencies, merely divide them by the frequency you need (in GHz). Line impedances are NOT a function of frequency.

Below is the frequency response of the Scardelletti splitter given a 50% shrink (arms are 45 degrees long). Looks like it doesn't achieve the same bandwidth as the Webb splitter, it rolls off quickly above the center frequency.