microstrippower-dividerRF
I finished the schematic for my 2.4GHz microstrip Wilkinson power divider. I am moving to the layout and trying to do the EM simulation, but I cannot figure out how to put a lumped element in the layout design. This is the error I am getting:
If anyone could help me put lumped elements into the EM simulation that would be greatly appreciated!! Thanks in advance!
I ran the calculation for you in Cadence SigXplorer (my favorite tool for this and a lot more):
This is a 10.25mil wide trace (sorry units on the image are in metric) to give 50R pretty closely.
Always use a 2D field solver for this (as you noticed, formulas are not enough).
Be aware that the SMA footprint may not be a smooth 50R without some great care as well. For this you can often get help from the connector manufacturer if you send them your stackup (and is deemed a worthy customer :-).
Disclaimer: I provide training in signal integrity often using tools kindly provided by Cadence. Other than that, I am not affiliated. Other tools can do the same thing. The only free one I have tried is called TNT.
Microwaves101 provides a good qualitative and intuitive explanation, and you seem to understand the idea. For a more rigorous derivation of the scattering matrix you can read section 7.3 (page 328) of Pozar's Microwave Engineering. In this case he uses what is called Even-Odd mode analysis, which he explains pretty well since it is the first time it is used in the text.
For example, why split in half and not some other ratio which would not result in complete cancellation?
The whole idea of the circuit is that it has the property that ports 2 and 3 are 180 degrees away (through the microstrips) and also 0 degrees away through the resistor. This circuit is the simplest way to achieve this property.
And wouldn't port 1 have some significance to the operation?
Yes. The circuit is only lossless if all ports are matched. If there are unequal voltages at ports 2 and 3 at any time power will be lost in the resistor. Assuming all ports are matches, this means the circuit can divide a signal losslessly (because the V2 and V3 will be equal and in phase) and can combine identical & in phase signals losslessly. It cannot combine independent signals losslessly*. This makes them a good candidate for use in solid state RF power amplifiers.
*It is impossible to construct a three-port lossless reciprocal network that is matched at all ports in general.
Best Answer
Unless you have EM model of resistor you cannot simulate it. Change the partition rule to circuit and run meshing and EM simulation. After that, create a component of this layout and place this as component this in a new schematic. The component looks like layout with pins at port ends and resistor. Now add the resistor in schematic and simulate S- Parameters.
Don't forget to place pins at the location you are placing resistor. They shouldn't be wrt to GND! Check out this example image I have cropped out from one of my design
Pins 1 is wrt gnd which acts as Port 1 where as I place a passive component between port 3 and 4.
Check out this link for procedure to converting layout to component and simulating it. This is example of microstrip filter.