NINA-B2 series - System integration manual
UBX-18011096 - R05
Design-in
Page 21 of 35
C1- Public
Table 5 summarizes the requirements for the antenna RF interface:
Item
Requirements
Remarks
Impedance
50
Ω
nominal characteristic
impedance
The impedance of the antenna RF connection must match the
50
Ω
impedance of the ANT pin.
Frequency range
2400 - 2500 MHz
Bluetooth.
Return loss
S
11
< -10 dB (VSWR < 2:1)
recommended
S
11
< -6 dB (VSWR < 3:1) acceptable
The Return loss or the S
11
, as the VSWR, refers to the amount
of reflected power, measuring how well the primary antenna
RF connection matches the 50
Ω
characteristic impedance of
the ANT pin.
The impedance of the antenna termination must match as
much as possible the 50
Ω
nominal impedance of the ANT pin
over the operating frequency range thus, maximizing the
amount of the power transferred to the antenna.
Efficiency
> -1.5 dB ( > 70% ) recommended
> -3.0 dB ( > 50% ) acceptable
The radiation efficiency is the ratio of the radiated power to
the power delivered to the antenna input; the efficiency is a
measure of how well an antenna receives or transmits.
Maximum gain
Refer to the data sheet [2]
The maximum antenna gain must not exceed the value
specified in type approval documentation to comply with the
radiation exposure limits specified by regulatory agencies.
Table 5: Summary of antenna interface (ANT) requirements for NINA-B221
Observe the following recommendations when selecting external or internal antennas:
•
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 appropriate gain figure (that is, 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 FCC in the United States).
3.3.2.1
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.
Table 6 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 6: 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.
