Integration Manual

ANNA-B4 series - System integration manual
UBX-21000517 - R03 Contents Page 25 of 76
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o Contact the PCB manufacturer for specific tolerance of controlled impedance traces. As FR-4
material exhibits poor thickness stability it gives less control of impedance over the trace
width.
• For PCBs with components larger than 0402 and dielectric thickness below 200 µm, add a
keep-out; that is, some clearance (void area) on the ground reference layer below any pin on the RF
transmission lines. This helps to reduce the parasitic capacitance to ground.
• Route RF traces with smooth shapes try not to exceed 45 ° bends and avoid acute angles. The
transmission lines width and spacing to GND must be uniform.
• Add GND stitching vias around transmission lines.
• Provide a sufficient number of vias on the adjacent metal layer. Include a solid metal connection
between the adjacent metal layer on the PCB stack-up to the main ground layer.
• To avoid crosstalk between RF traces and Hi-impedance or analog signals, route RF transmission
lines as far from noise sources (like switching supplies and digital lines) and any other sensitive
circuit.
• Avoid stubs on the transmission lines. Any component on the transmission line should be placed
with the connected pin located over the trace. Also avoid any unnecessary components on RF
traces.
RF connector design
If an external antenna is required, the designer should consider using a proper RF connector. The
designer must verify the compatibility between plugs and receptacles used in the design.
Based on the declarations of the respective manufacturers, Table 13 suggests some RF connector
plugs that can be used by designers to connect RF coaxial cables.
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 13: U.FL compatible plug connector
The Hirose U.FL-R-SMT RF receptacles (or similar parts) require a suitably mated RF plug from the
same connector series. Due to wide usage of this connector, several manufacturers offer compatible
equivalents. The RF plug is normally 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 of the cable assembly include:
• RF plug type: select U.FL or equivalent
• Nominal impedance: 50 
• Cable thickness: Typically, 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)
Note 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.