NINA-B1 series - System Integration Manual
UBX-15026175 - R06
Design-in
Page 32 of 48
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 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
UFL 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 UF.L 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.
3.2.2.2
Integrated antenna design
If integrated antennas are used, the transmission line is terminated by the integrated antennas themselves. The
following guidelines should be followed:
•
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 8).
•
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-B1 modules.
3.2.3
On-board antenna design (NINA-B112 only)
Keep a minimum clearance of 5 mm between the antenna and the casing. Keep a minimum of 10 mm free
space from the metal around the antenna including the area below the antenna. If a metal enclosure is required,
NINA-B111 with antenna pin has to be used.
