NINA-B1 series - System integration manual
UBX-15026175 - R16
Design-in
Page 40 of 63
C1-Public
Table 8 suggests some RF connector plugs that can be used by the designers to connect RF coaxial
cables based on the declaration of the respective manufacturers. The Hirose U.FL-R-SMT RF
receptacles (or similar parts) require a suitable mated RF plug from the same connector series. Due
to wide usage of this connector, several manufacturers offer compatible equivalents.
Manufacturer
Series
Remarks
Hirose
U.FL® Ultra Small Surface Mount Coaxial Connector Recommended
I-PEX
MHF® Micro Coaxial Connector
Tyco
UMCC® Ultra-Miniature Coax Connector
Amphenol RF
AMC® Amphenol Micro Coaxial
Lighthorse Technologies, Inc.
IPX ultra micro-miniature RF connector
Table 8: U.FL compatible plug connector
Typically, the RF plug is available as a cable assembly. Different types of cable assembly are available;
the user should select the cable assembly best suited to the application. The key characteristics are:
•
RF plug type: select U.FL or equivalent
•
Nominal impedance: 50
Ω
•
Cable thickness: Typically from 0.8 mm to 1.37 mm. Select thicker cables to minimize insertion
loss.
•
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. 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.
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).
