Keysight Technologies PD1000A, Operating Manual

Page: 32 / 44

32 Keysight PD1000A Test Fixture Operating Guide
Customizing an SMD Test Fixture
Example:
See Figure 19 below. Assume a PC Board of FR4 material with a thickness (h) of
0.5 mm. If t = 1 mm (the thickness of the trace), then w ≈ 0.877 mm. The distance
from the RF Line to GND is >2 t , or
≈
2 mm. These are only approximations.
The following microstrip line equations helps determine the width and length of
the microstrip line for a give impedance.(Z
o
). The substrate parameters
ε
r
and h
are required.
Figure 19 Microstrip Line Example for 50
Ω
Impedance
For the following equation, the distance between the RF trace line and the GND should be greater
than twice thne thickness of teh PC Board trace.sd S W ZZZZ
To use the following microstrip substrate equations, the distance
between the RF trace line and the GND must be greater than twice
the thickness of the PC Board trace.
ε
eff
ε
r
1 +
2
-------------
ε
r
1 –
2
-------------
1
1 12
H
W
-----
+
------------------------- 0.04 1
W
H
----- –
 
 
2
+ + =
Z
o
60
ε
eff
-------------
8
H
W
-------
W
4
H
------- +
 
 
ln Ω
=
Where: H=h-2t
ε
eff
=
Effective relative
ε
r
ε
r
=
Dielectric Constant
Z
o
=
Characteristic impedance (use 50 Ω )