NINA-B4 series - System integration manual
UBX-19052230 - R09
Design-in
Page 24 of 61
C1-Public
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A de-facto standard for SMA connectors implies the usage of reverse polarity connectors (RP-
SMA) on Wi-Fi and Bluetooth end products to make it more difficult for end users to replace the
antenna with higher gain versions that exceed the 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 (clearance or void) 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 and retain the RF line impedance of 50
. For
example, the active pad of the UF.L connector must have a GND keep-out (clearance or void area)
–
at least on the first inner layer to reduce parasitic capacitance to ground.
2.6.1.2
External antenna design-in (NINA-B4x1)
Observe the following guidelines if the design requires an external antenna to be mounted directly on
the main PCB:
•
The antenna design process should begin at the start of the product design process. Prototype
PCBs with antenna assembly are useful in estimating overall efficiency and radiation pattern 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 to a minimal size that is not less than a
quarter of a wavelength of the minimum frequency that shall be radiated. The 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. These parts can absorb part of the radiated power, shift the resonant frequency of the
antenna, or affect the antenna radiation pattern.
•
Strict
adherence to the antenna manufacturer’s
guidelines describing the installation and
deployment of the antenna system, including the PCB layout and matching circuitry, is strongly
advised.
•
In addition to the custom PCB and product restrictions, antennas may require tuning/matching to
comply with the required certification schemes. 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 also
•
The 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.
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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-B4 modules.
2.6.1.3
RF transmission line design (NINA-B4x1)
RF transmission lines connecting the
ANT
pad with the related antenna connector or antenna, must
be designed with a 50
impedance characteristic.