Integration Manual

SARA-R4/N4 series - System Integration Manual

UBX-16029218 - R11 Design-in Page 81 of 157

Min.

250 µm

Min. 400 µm

GND

ANT

GND clearance

on buried layer very close to top layer

below ANT pad

GND clearance

on top 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.

Figure 32 and Figure 33 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 µm

270 µm

760 µm

L1 Copper

L3 Copper

L2 Copper

L4 Copper

FR-4 dielectric

380 µm 500 µm500 µm

Figure 32: Example of 50  coplanar waveguide transmission line design for the described 4-layer board layup