NINA-B50 series - Hardware integration manual
UBX-22021116 - R02
Design-in
Page 23 of 57
C1-Public
Typically, the RF plug is available as a cable assembly. Different types of cable assemblies are
available, and the user should select the cable assembly best suited for the application. The key
characteristics of an appropriate plug include:
•
RF plug type: Select U.FL or equivalent
•
Nominal impedance: 50
•
Cable thickness: Select thicker cables, typically those with a thickness between 0.8 mm to
1.37 mm, to minimize insertion loss.
•
Cable length: The standard cable length is typically 100 mm or 200 mm; custom lengths are
available on request. Select shorter cables to minimize insertion loss.
•
RF connector terminating the other side of the cable: for example, another U.FL (for board-to-board
connection) or SMA (for panel mounting).
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 suggests that the usage of reverse polarity connectors
(RP-SMA) on Wi-Fi and Bluetooth end products make it more difficult for end users to replace the
antenna with higher gain versions that exceed regulatory limits.
Figure 8: U.FL connector layout showing top layer (left) and inner layer 1 (right)
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 a void GND keep-out clearance 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 in the area below the connector
between the GND land pads.
If the connector’s RF pad size is wider than the microstrip, remove the GND layer beneath the RF
connector to minimize the stray capacitance and keep the RF line to an impedance of 50
Ω
. To reduce
parasitic capacitance-to-ground for example, the active pad of the U.FL. connector must include (at
the very least) a void GND keep-out clearance area on the first inner layer.
3.2.3.2
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 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.
