4.4 Stripline
A stripline (triplate) transmission line consists of a flat metallic trace centred between two infinite ground planes. The trace width is w and the distance between the ground planes is b (see Figure 4.9). The entire space between the ground planes is filled with a homogeneous dielectric material with a relative permittivity of εr. In real striplines the substrate width bs is finite and the centre strip conductor has a thickness t. The fundamental wave mode is a TEM wave. The transversal magnetic field circles around the centre strip conductor. The electric field points from the strip conductor to ground.
4.4.1 Characteristic Impedance
In the literature we find approximate formulas for the characteristic impedance of striplines. A compact formula from [12] gives us
with an effective trace width w′ of
4.35
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