Differential transmission line with a set relationship to a ground conductor and method of manufacturing

A printed circuit board comprising:

• a dielectric layer having a first surface and a second surface;
• first and second transmission lines formed on the one first surface of said dielectric layer and constituting a differential transmission path;
• and
• a ground conductor layer formed on the second surface of said dielectric layer, wherein
• said ground conductor layer is arranged to be opposite to at least part of said first transmission line and at least part of said second transmission line in a width direction of said first and second transmission lines with said dielectric layer sandwiched between said ground conductor layer and said first and second transmission lines, and
• a width W1 of said first transmission line, a width W2 of said second transmission line, a spacing S between said first transmission line and said second transmission line, and a width Wg of said ground conductor layer in an arbitrary cross section perpendicular to said first and second transmission lines satisfy a relationship of Wg<(W1+W2+S) and S≦0.8 Wg, and further satisfy a relationship of Wg/S≧2.00 and W1>2S and W2>2S.