Component reference plane in microwave office

Hello,

When using lumped elements in a microstrip circuit simulation in microwave office, what is the reference plane of the connection? Is it the end of the component or does it have to do anything with the component footprint?

Best regards.

You have opended a big can of worms! It depends. For a RLC SMT components the reference plane is the junction between the pad and your microstrip. You may need to place a step discontinuity between the pad and your microstrip.

Of course all this assumes the component was modeled/measured properly to include the effects of the pads. The pads are a function of your substrate which the component vendor has no idea about. You may even have different pad dimensions. So if you download s-parameters off the web (or use built in models) they need to specify exactly how they measured. If they don't detail the method then don't trust the measurements.

Modelithics provides component models that have scalable pads. They are valid for many sizes and substrates. They also provide great detail into how they measured the parts. Read some of their papers for a better explanation.

http://www.modelithics.com/

For drop in devices, such as power transistors, this is not as much of a problem since the reference plane goes up to the package of the device. However there is fringing capacitance from the pad which the vendor may have not bothered to remove from the measurement.