NINA-B50 series - Hardware integration manual
UBX-22021116 - R02
Design-in
Page 20 of 57
C1-Public
To ensure proper performance of the application product, carefully follow the guidelines outlined
below. Note also that the RF certification of the module is extended through to the application design.
•
External antennas, including, linear monopole classes:
o
Place the module and antenna in any convenient area on the board. External antennas do
n’t
impose any restriction on where the module is placed on the PCB.
o
Select antennas with an optimal radiating performance in the operating bands. The radiation
performance depends mainly on the antennas.
o
Choose RF cables that offer minimum insertion loss. Unnecessary insertion loss is introduced
by low quality or long cables. Large insertion losses reduce radiation performance.
o
Use a high-quality 50
coaxial connector for proper PCB-to-RF-cable transition.
•
Integrated antennas, such as patch-like antennas:
o
Internal integrated antennas impose some physical restrictions on the PCB design. Given that
the orientation of the ground plane related to the antenna element must be considered:
-
Integrated antennas excite RF currents on its counterpoise, typically the PCB ground plane
of the device that becomes part of the antenna; its dimension defines the minimum
frequency that can be radiated. Therefore, the ground plane can be reduced to a minimum
size that should not be smaller than a quarter of the wavelength of the minimum frequency
that has to be radiated.
-
Find a numerical example to estimate the physical restrictions on a PCB, where:
Frequency = 2.4 GHz
→
Wavelength = 12.5 cm
→
Quarter wavelength = 3.5 cm in free space
or 1.5 cm on a FR4 substrate PCB.
•
Choose antennas with optimal radiating performance in the operating bands. Radiation
performance depends on the complete product and antenna system design, including the
mechanical design and usage of the product.
summarizes the requirements for the
antenna RF interface.
Item
Requirements
Remarks
Impedance
50
nominal characteristic impedance The impedance of the antenna RF connection must match
the 50
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 S
11.
As a parameter of the of the standing
waves ratio (VSWR) measurement, S
11
refers to the amount
of reflected power. This parameter indicates how well the
primary antenna RF connection matches the 50
characteristic impedance of the ANT pin.
To maximize the amount of the power transferred to the
antenna, the impedance of the antenna termination must
match (as much as possible) the 50
nominal impedance of
the ANT pin over the entire operating frequency range.
Efficiency
> -1.5 dB ( > 70% ) recommended
> -3.0 dB ( > 50% ) acceptable
The radiation efficiency is the ratio of the radiated power
against the power delivered to the antenna input; the
efficiency is a measure of how well an antenna receives or
transmits.
Maximum Gain
+3 dBi
Although higher gain antennas can be used, these must be
evaluated and/or certified. To comply with regulatory
agencies radiation exposure limits, the maximum antenna
gain must not exceed the value specified in the
Table 5: Summary of antenna interface requirements for NINA-B50