Microstrip Filling Factor versus Relative Dielectric Constant Given fixed Line Impedance
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The question arose given a fixed microstrip transmission line characteristic impedance how does the percentage of the field in the substrate change? This is called the filling factor:
Keff=ER*FF+1x(1-FF)
It is the fraction of the field in the substrate. I calculated the following values:
- FF=(Keff-1)/(ER-1)
- Dk=4 Z0=51 Deff = 3.07 which yields a filling factor of 0.69
- Dk=10 Z0=50.5 Deff = 6.72 which yields a filling factor of 0.635
Thus it appears that the filling factor goes down with Dk as Z0 is held constant.