NORA-W36 series - System integration manual
UBX-22021120 - R01
Design-in
Page 15 of 48
C1-Public
•
Ensure solid metal connection of the adjacent metal layer on the PCB stack-up to main ground
layer, providing enough vias on the adjacent metal layer.
•
Route RF transmission lines far from any noise source (for example, switching supplies and digital
lines) and from any sensitive circuit to avoid crosstalk between RF traces and high impedance or
analog signals.
•
Avoid stubs on the transmission lines, any component on the transmission line should be placed
with the connected pad over the trace. Also avoid any unnecessary components on RF traces.
3.2.2
Antenna design (NORA-W361)
NORA-W361 is suited for designs when an external antenna is needed due to mechanical integration
or placement of the module.
Designers must take care of the antennas from all perspective at the beginning of the design phase
when the physical dimensions of the application board are under analysis/decision, as the RF
compliance of the device integrating NORA-W361 module with all the applicable required certification
schemes heavily depends on the radiating performance of the antennas. Designers are encouraged
to consider one of the u-blox suggested antenna part numbers and follow the layout requirements.
•
External antennas such as those listed in the
o
External antennas
don’t
imply physical restriction to the design of the PCB where the module
is mounted.
o
The radiation performance mainly depends on the antennas. It is required to select antennas
with optimal radiating performance in the operating bands.
o
RF cables should carefully be selected with minimum insertion losses. Additional insertion loss
will be introduced by low quality or long cable. Large insertion loss reduces radiation
performance.
o
A high quality 50
coaxial connector provides proper PCB-to-RF-cable transition.
•
Integrated antennas such as patch-like antennas:
o
Internal integrated antennas imply physical restriction to the PCB design:
Integrated antenna excites RF currents on its counterpoise. Typically, the PCB ground plane of
the device that becomes part of the antenna, and its dimension defines the minimum
frequency that can be radiated. Therefore, the ground plane can be reduced to a minimum size
that should be similar to the quarter of the wavelength of the minimum frequency that has to
be radiated. Given that, the orientation of the ground plane related to the antenna element
must be considered.
The RF isolation between antennas in the system must be as high as possible and the
correlation between the 3D radiation patterns of the two antennas must be as low as possible.
In general, an RF separation of at least a quarter wavelength between the two antennas is
required to achieve a maximum isolation and low pattern correlation. Increased separation
should be considered, if possible, to maximize the performance and fulfil the requirements
described in
. As a numerical example, the physical restriction to the PCB design can be
considered as shown below:
Frequency = 2.4 GHz
→
Wavelength = 12.5 cm
→
Quarter wavelength = 3.125 cm
1
o
Radiation performance depends on the whole product and antenna system design, including
product mechanical design and usage. Antennas should be selected with optimal radiating
performance in the operating bands according to the mechanical specifications of the PCB and
the whole product.
1
Wavelength referred to a signal propagating over the air.
