NINA-B1 series - System integration manual
UBX-15026175 - R16
Design-in
Page 39 of 63
C1-Public
The RF isolation between antennas in the system has to be as high as possible and the correlation
between the 3D radiation patterns of the two antennas has to be as low as possible. In general, an
RF separation of at least a quarter wavelength between the two antennas is required to achieve a
maximum isolation and low pattern correlation; increased separation should be considered if
possible, to maximize the performance and fulfil the requirements in Table 7.
As numerical example, the physical restriction to the PCB design can be considered as shown
below:
Frequency = 2.4 GHz
Wavelength = 12.5 cm
Quarter wavelength = 3.125 cm
•
Radiation performance depends on the whole product and antenna system design, including
product mechanical design and usage. Antennas should be selected with optimal radiating
performance in the operating bands according to the mechanical specifications of the PCB and the
whole product.
Table 7 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 low energy.
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 Section 5
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 7: Summary of antenna interface (ANT) requirements for NINA-B1
In both the cases, 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 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).
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.
1
Wavelength referred to a signal propagating over the air.
