Why should the (conductor thickness)/(dielectric thickness) ratio of a micro strip not exceed 0.1?

When I am attempting to define a microstrip transmission line in MATLAB, I'm getting an error that the (conductor thickness)/(dielectric thickness) ratio should not exceed 0.1. It is unclear in the RF Budget Analyzer App which parameters this applies to when defining the transmission line.

Additionally, I believe that, in reality, a widely used plate thickness is 35um, with the dielectric height being as small as 100um resulting in a ratio of 0.35, and with these parameters that MATLAB throws below error:

The (conductor thickness)/(dielectric thickness) ratio cannot exceed 0.1

Why is this the limitation? Also, is there a way to get around this limitation?

Answer 1

[MathWorks Support Team]

A list is provided below to clarify the parameters of the RF Budget Analyzer, and which errors the parameters relate to.

• Width Parameter = Conductor Width
• Height Parameter = Dielectric Thickness
• Thickness Parameter = Conductor Thickness

There is limit on the thickness ratio in order to maintain the accuracy of the equation used to model the microstrip as referenced in the book "Microstrip Lines and Slotlines, 2nd Edition" of which is also referenced by the corresponding "rfckt.microstrip" documentation.

Finally, there is a way around the limitation, but it will require another tool to extract parameters of the microstrip. For example, if the loss and the phase velocity are extracted, you can use the 'rfckt.txline' following the linked documentation with more information.