JODY-W2 - System integration manual
UBX-18068879 - R14
Design-in
Page 25 of 84
C1 - Public
2.2.2.1
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.
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 18: 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. Thicker cables 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)
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 end-user accessible Wi-Fi and Bluetooth interfaces to increase the difficulty 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
. Some examples are provided
below:
o
SMA Pin-Through-Hole connectors require GND keep-out (clearance or void area) on all the
layers around the central pin up to annular pins of the four GND posts.
o
U.FL surface mounted connectors require no conductive traces (that is, clearance, a void area)
in the area below the connector between the GND land pins.
•
If the RF pin size on the connector is wider than the microstrip, remove the GND layer beneath the
RF connector to minimize the stray capacitance thus keeping the RF line 50
. For example, the
active pin of U.FL connector must have a GND keep-out at least on the first inner layer to reduce
parasitic capacitance to ground.
2.2.2.2
Integrated antenna design
If integrated antennas are used, the transmission line is terminated by the antennas themselves.
Follow the guidelines mentioned below:
