Stripline Transmission Lines
[file: sline.mcd]
Formulas included in this spreadsheet:
-
Stripline characteristic impedance ZSTRIP()
-
Offset stripline characteristic impedance ZOFFSET()
-
Stripline propagation delay PSTRIP()
-
Stripline trace inductance LSTRIP()
-
Offset stripline inductance LOSTRIP()
-
Stripline trace capacitance CSTRIP()
-
Offset stripline capacitance COSTRIP()
Formulas are from Seymour Cohn,
"Problems in Strip Transmission
Lines," MTT-3, No. 2, March 1955,
pp. 199-126.
This material is summarized in
Harlan Howe, Stripline Circuit
Design, Artech House, Norwood, MA,
1974.
Variables used:
-
h1 Trace height above lower ground plane (in.)
-
h2 Trace headroom below upper ground plane (in.)
-
b Separation between ground planes, b = h1 + h2 + t (in.)
-
w Trace width (in.)
-
t Trace thickness (in.)
-
er Trace thickness (in.)
-
x Trace length (in.)
Stripline characteristic impedance (W:)
Accuracy of better than 1.3% is
obtained under the following conditions:
t/b < 0.25
t/w < 0.11
er unrestricted
NOTE: formula ZSTR_K1() corrected per instructions
from Robert Canright of Richardson, TX.
Thanks, Robert.
For skinny traces (w/b < 0.35)
For wide traces (w/b > 0.35)
Composite formula picks skinny or wide model depending on w/b ratio:
Rarely are the two parameters h1 and h2 equal in practice. The
more common case is an asymmetric stripline having the conducting
trace offset to one side.
Offset, or asymmetric, stripline characteristic impedance (W)
(no accuracy guaranteed):
Propagation delay of stripline (s/in.):
(same formula for
centered or offset
stripline)
Inductance of stripline (H):
In the equation above, we can assume a relative permittivity of 1.;
it doesn't effect the answer.
Inductance of offset stripline (H):
Capacitance of stripline (F):
In the equations above and below, we must use
the relative permittivity.
Capacitance of offset stripline (F):
_______________________________________________
Example stripline calculations
Ground plane separation (in.)
Width of trace (in.)
(1-oz copper
plating weight)
Thickness of trace (in.)
Length of wire (in.)
Relative electric
permeability (affects
capacitance, but not
inductance)
Impedance (W):
Total inductance (H):
Same result in nH:
Inductance per in. (H):
Total capacitance (F):
Same result in pF:
Capacitance per in. (F):
Tolerance effects:
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