SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R11
Design-in
Page 81 of 157
M in.
250
µ
m
M in. 40 0
µ
m
GND
ANT
GND clearance
on buried layer very close t o t op layer
below ANT pad
GND clearance
on t op layer
around ANT pad
Figure 31: GND keep-out area on top layer around ANT pad and on very close buried layer below ANT pad
Guidelines for RF transmission line design
Any RF transmission line, such as the ones from the
ANT
pad up to the related antenna connector or up
to the related internal antenna pad, must be designed so that the characteristic impedance is as close as
possible to 50
.
RF transmission lines can be designed as a micro strip (consists of a conducting strip separated from a
ground plane by a dielectric material) or a strip line (consists of a flat strip of metal which is sandwiched
between two parallel ground planes within a dielectric material). The micro strip, implemented as a coplanar
waveguide, is the most common configuration for printed circuit board.
provide two examples of suitable 50
coplanar waveguide designs. The first
example of RF transmission line can be implemented in case of 4-layer PCB stack-up herein described, and
the second example of RF transmission line can be implemented in case of 2-layer PCB stack-up herein
described.
35
µ
m
35
µ
m
35
µ
m
35
µ
m
270
µ
m
270
µ
m
760
µ
m
L1 Copper
L3 Copper
L2 Copper
L4 Copper
FR-4 dielect ric
FR-4 dielect ric
FR-4 dielect ric
380
µ
m 50 0
µ
m
50 0
µ
m
Figure 32: Example of 50
coplanar waveguide transmission line design for the described 4-layer board layup
