NINA-B2 series - System Integration Manual
UBX-18011096 - R03
Contents
Page 17 of 30
•
Cable length: Standard length is typically 100 mm or 200 mm; custom lengths may be available
on request. Select shorter cables to minimize insertion loss.
•
RF connector on the other side of the cable: For example, another U.FL. (for board-to-board
connection) or SMA (for panel mounting)
Consider that SMT connectors are typically rated for a limited number of insertion cycles.
Additionally, the RF coaxial cable may be relatively fragile compared to other types of cables. To
increase application ruggedness, connect 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 to increase the difficulty for the end user to replace
the antenna with higher gain versions and exceed regulatory limits.
The following recommendations apply 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 connector’s RF pad size 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.
3.3.2.2
Integrated antenna design
If integrated antennas are used, the transmission line is terminated by the integrated antennas
themselves. Follow the guidelines mentioned below:
•
The antenna design process should begin at the start of the whole product design process. Self-
made PCBs and antenna assembly are useful in estimating overall efficiency and 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 large enough according to the related integrated antenna requirements.
The ground plane of the application PCB may be reduced down to a minimum size that must be
similar to one quarter of wavelength of the minimum frequency that has to be radiated; however
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 PCB layout and matching circuitry.
•
Further 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 4).
•
RF section may be affected by noise sources like hi-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 NINA-B2 modules.
