Geometric Parameter Definitions
W: 

trace width 
T: 
trace thickness 
H (/H1) 
height of trace or dielectric above return plane 
C: 
distance between the differential stripline pair 
er: 
relative permittivity of the dielectric 
Electrical Parameter Definitions
Zo: 

characteristic impedance 
Zc: 
effective characteristic impedance including the capacitance of distributed loads 
Tpd: 
propagation delay 
Lo: 
inductance per unit length 
Co: 
capacitance per unit length 
Acknowledgements:
The source for formulas used in this calculator (except where otherwise noted) is:
IPCD317A, Design Guidelines for Electronic Packaging Utilizing HighSpeed
Techniques, Jan 1995; Section 5, pp. 13  36.
THESE FORMULAS ARE APPROXIMATIONS!
They should not be used when a high degree
of accuracy is required.
The transmission line calculator concept was developed by Douglas Brooks and is
described in his paper:
PCB Impedance Control: Formulas and Resources, Printed Circuit
Design Magazine, March 1998.
A copy of his paper and a similar transmission line calculator that runs on a PC can be obtained
from UltraCAD Design, Inc.
