NORA-B1 series - System integration manual
UBX-20027617 - R02
Design-in
Page 26 of 58
C1-Public
Consider that SMT connectors are typically rated for a limited number of insertion cycles. In addition,
the RF coaxial cable may be relatively fragile compared to other types of cables. To increase
application ruggedness, connect the U.FL connector to a more robust connector such as SMA fixed
on panel.
☞
A de-facto standard for SMA connectors implies the usage of reverse polarity connectors (RP-
SMA) on Wi-Fi and Bluetooth end-products. The standard makes it more difficult for the end users
to replace the antenna with higher gain versions and exceed the regulatory limits.
Observe these recommendations for proper layout of the connector:
•
Strictly follow the connector manufacturer’s recommended layout:
o
SMA Pin-Through-Hole connectors require GND keep-out (that is, clearance, a void area) on all
the layers around the central pin up to annular pads of the four GND posts.
o
U.FL surface mounted connectors require no conductive traces (that is, clearance, a void area)
in the area below the connector between the GND land pads.
•
If the RF pad size of the connector is wider than the micro strip, remove the GND layer beneath the
RF connector to minimize the stray capacitance thus keeping the RF line 50
Ω
. For example, the
active pad of the U.FL connector must have a GND keep-out (that is, clearance, a void area), at
least on the first inner layer to reduce parasitic capacitance to ground.
4.3.2.2
Integrated antenna design
The following guidelines should be followed when integrating an antenna onto the host PCB:
•
Antenna integration should begin at the start of the end-product design process. Self-made PCBs
and antenna assemblies are useful in estimating overall efficiency and the radiation path of the
intended design.
•
Use antennas designed by an antenna manufacturer providing the best possible return loss (or
VSWR).
•
Provide a ground plane that is large enough to meet the related integrated antenna requirements.
The ground plane of the application PCB can be reduced to a minimum size of one-quarter
wavelength of the minimum frequency that needs to be radiated, although overall antenna
efficiency may benefit from larger ground planes.
•
Proper placement of the antenna and its surroundings is also critical for antenna performance.
Avoid placing the antenna close to conductive or RF-absorbing parts such as metal objects, ferrite
sheets and so on as they may absorb part of the radiated power or shift the resonant frequency of
the antenna or affect the antenna radiation pattern.
•
It is highly recommended to strictly follow the detailed and specific guidelines provided by the
antenna manufacturer regarding correct installation and deployment of the antenna system,
including the PCB layout and matching circuitry.
•
In addition to the custom PCB and product restrictions, antennas may require tuning/matching to
comply with all the applicable required certification schemes. It is recommended to consult the
antenna manufacturer for the design-in guidelines and plan the validation activities on the final
prototypes like tuning/matching and performance measures (see Table 9).
•
The RF section may be affected by noise sources like high-speed digital buses. Avoid placing the
antenna close to buses such as DDR or consider taking specific countermeasures like metal
shields or ferrite sheets to reduce the interference.
⚠
Take care of interaction between co-located RF systems like LTE sidebands on 2.4 GHz band.
Transmitted power may interact or disturb the performance of NORA-B1 modules.
