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While selecting external or internal antennas, the following recommendations should be observed:
•
Select antennas that provide optimal return loss (or VSWR) figure over all the operating
frequencies.
•
Select antennas that provide optimal efficiency figure over all the operating frequencies.
•
Select antennas that provide an appropriate gain figure (based on the combined antenna
directivity and efficiency figure), so that the electromagnetic field radiation intensity does not
exceed the regulatory limits specified in some countries (for example, by the FCC in the United
States).
RF Connector Design
If an external antenna is required, the designer should consider using a proper RF connector. It is the
responsibility of the designer to verify the compatibility between plugs and receptacles used in the
design.
Table 9
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
Hirose
I-PEX
Tyco
Amphenol RF
Lighthorse Technologies, Inc.
Table 9: 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
•
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 the 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 the regulatory limits.
UBX-17056748 - R13
C1-Public
Series
U.FL® Ultra Small Surface Mount Coaxial Connector
MHF® Micro Coaxial Connector
UMCC® Ultra-Miniature Coax Connector
AMC® Amphenol Micro Coaxial
IPX ultra micro-miniature RF connector
Design-in
NINA-B3 series - System integration manual
Remarks
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