Broadside-coupled Stripline

Broadside-coupled offset stripline with two substrate dielectrics, H1 and H2

This apparently simple construction is actually one of the most difficult to fabricate to produce consistent impedance results.

Despite having internal layers with minimal processing, the most common structure is that with both traces overlaid for maximum coupling.

Inner-layer mis-registration and slight offsets and differences in etching combine to make this more difficult to achieve consistent results, particularly if the traces are fine-line.

Broadside-coupled offset stripline with three substrate dielectrics, H1, H2 and H3

The Si9000 broadside-coupled model assumes symmetry of dielectric in the two H2 and H3 layers — the two layers will normally be fabricated from the same material, i.e. with the same dielectric constant.

Note that in the Broadside-coupled Stripline case the traces are trapezoidal in profile and width, W₂ refers to the trace width nearest the surfaces, W₁ refers to the trace width nearest the center.