Ublox NINA-B3 Series System Integration Manual page 35

• External antennas, such as a linear monopole:
External antennas basically do not impose any physical restrictions on the design of the PCB
o
where the module is mounted.
The radiation performance mainly depends on the antennas. It is required to select antennas
o
with optimal radiating performance in the operating bands.
RF cables should be carefully selected with minimum insertion losses. Additional insertion loss
o
will be introduced by low quality or long cables. Large insertion loss reduces radiation
performance.
A high quality 50  coaxial connector provides proper PCB-to-RF-cable transition.
o
• Integrated antennas such as patch-like antennas:
Internal integrated antennas impose physical restrictions on the PCB design:
o
An integrated antenna excites 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. As the orientation of the ground plane related to the antenna element
must be considered, the ground plane can be reduced to a minimum size that is similar to the
quarter of the wavelength of the minimum frequency that needs to be radiated.
The RF isolation between antennas in the system must be as high as possible and the
correlation between the 3D radiation patterns of the two antennas must 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 fulfill the requirements in
Table 8.
As a 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 entire product and antenna system design, including
o
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 entire product.
Table 8 summarizes the requirements for the antenna RF interface.
Item Requirements
Impedance
50  nominal
characteristic impedance
Frequency Range 2400 - 2500 MHz
Return Loss S < -10 dB (VSWR < 2:1)
11
recommended
S < -6 dB (VSWR < 3:1)
11
acceptable
Efficiency > -1.5 dB ( > 70% )
recommended
> -3.0 dB ( > 50% )
acceptable
Maximum Gain +3 dBi
Table 8: Summary of antenna interface (ANT) requirements for NINA-B3
1 Wavelength referred to a signal propagating over the air
UBX-17056748 - R13
C1-Public
NINA-B3 series - System integration manual
Remarks
The impedance of the antenna RF connection must match the 50 
impedance of the ANT pin.
Bluetooth low energy.
The Return loss or the S , as the VSWR, refers to the amount of reflected
11
power, measuring how well the primary antenna RF connection matches the
50  characteristic impedance of the ANT pin.
The impedance of the antenna termination must match as much as possible
the 50  nominal impedance of the ANT pin over the operating frequency
range, thus maximizing the amount of the power transferred to the antenna.
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.
Higher gain antennas can be used, but these must be evaluated and/or
certified. See also Regulatory information and
Design-in
1
requirements.
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