2 microstrip capacitance with dielectric

[hops1]

Hi guys,

I've been trying to figure out how the capacitance of two microstrips, separated a distance d, are influenced by the presence of a dielectric. The dielectric will be a height (h) above the strips and has restricted movement. Using the electric potential I am able to derive a function for the capacitance in absence of the dielectric. However I hit a wall when trying to incorporate the dielectric.

Is there a way to approximate this even with a 2-wire system with a dielectric equidistant from the wires at a given height?

Any suggestions, or nudge in the right direction is appreciated

Thanks

 

[tech99]

I presume the microstrips are on a thin (about lambda/100) layer of dielectric above a conducting sheet. In this situation you can visualise two separate transmission lines which are single conductor lines above a ground plane. When driven in balanced fashion, Z0 will be double that of each line. The capacitance is predominantly between each line and ground. If a dielectric is placed above them, the main electric field does not encompass the dielectric (being between the strip and ground) and my opinion is that its effect will be very small.