![]() The transmission coefficient (essentially S21 or S31 in S-parameters) can be calculated from the reflection coefficient at port 1 assuming that the network is lossless: Next, following Cohn's paper, we can easily arrive at the reflection coefficient at port 1, because it is the same as the even-mode reflection coefficient: The resistor values all get chopped in half:įrom the even and odd mode schematics, the reflection coefficients can be calculated from the impedance looking in (Zin) using the transformer equation: In this case a virtual ground lies across the axis of symmetry. In the odd mode, the excitations are 180 degrees out of phase. Then the voltages across the isolation resistors are zero and they can be ignored: The even mode analysis is done by assuming that the excitations on ports 2 and 3 are in-phase. We adopted Cohn's designations of the R's and Z's starting with subscript "1" closest to the split ports: ![]() The analysis below is also explained in Cohn's paper.įirst, look at the generic multi-section Wilkinson schematic. Some day the even/odd mode technique will be better explained on this page. We merely put his math it into a spreadsheet (OK, we also had to put in some Chebyshev polynomials, and we're working on adding the isolation resistor calculations that Harlon Howe described in his book Stripline Circuit Design but Rome wasn't built in a day, was it?) Transformer design calculation excel full#The full technique is described in a 1968 paper by Seymour Cohn in an IEEE paper titled A Class of Broadband Three-Port TEM-Mode Hybrids. The trick to making a mathematical model of Wilkinson's power splitter is to apply even and odd mode analysis. We still haven't perfected the math, but our new spreadsheet will allow you to fiddle with the isolation resistors and watch their affects on isolation and reflection coefficients in (almost) real time. Now we have an Excel spreadsheet that analyzes the Wilkinson divider, including the isolation resistors, to give you the full three-port response. Transformer design calculation excel how to#We showed you how to do that here (look at Example 3). ![]() Using transformer analysis is an easy method to select line impedances of a multi-section Wilkinson splitter. The selection of "optimum" resistor values for a design bandwidth beyond the N=2 Wilkinson is messy and almost always forces engineers to use an optimizer which is offered in expensive software such as Agilent's ADS, which not everyone has access to. New for August 2008! This page came about from some email correspondence with Tim who lamented about the lack of a straightforward way of selecting isolation resistors in a multi-section Wilkinson. ![]() Click here to go to our main page on Wilkinson power splittersĬlick here to go to our page on multisection Wilkinsons ![]()
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