NORA-W2 series - Hardware integration manual
UBX-22005177 - R01
Design-in
Page 14 of 61
C1
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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 not
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:
-
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, given that the orientation of the ground plane related to the
antenna element must be considered.
-
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.
•
Make the RF isolation between the system antennas as high as possible, and the correlation
between the 3D radiation patterns of the two antennas as low as possible. In general, RF
separation of at least a quarter wavelength between the two antennas is required to achieve some
isolation and low pattern correlation. If possible, increase the separation to maximize the
performance and fulfill the requirements in
Item
Requirements
Remarks
Impedance
50
nominal characteristic
impedance
The impedance of the antenna RF connection must match
the 50
impedance of Antenna pins.
Frequency Range
2400 - 2500 MHz
5150 - 5850 MHz
For 802.11b/g/n/ax and Bluetooth.
For 802.11a/n/ac/ax.
Return Loss
S11 < -10 dB (VSWR < 2:1)
recommended
S11 < -6 dB (VSWR < 3:1) acceptable
The Return loss or the S11, as the VSWR, refers to the
amount of reflected power, measuring how well the primary
antenna RF connection matches the 50
characteristic
impedance of antenna pins.
The impedance of the antenna termination must match as
much as possible the 50
nominal impedance of antenna
pins over the operating frequency range, to maximize the
amount of power transferred to the antenna.
Efficiency
> -1.5 dB ( > 70% ) recommended
> -3.0 dB ( > 50% ) acceptable
Radiation efficiency is the ratio of the radiated power to the
power fed to the antenna input: the efficiency is a measure
of how well an antenna receives or transmits.
Maximum Gain
To comply with regulatory agencies radiation exposure
limits, the maximum antenna gain must not exceed the
value specified in type approval documentation.
Table 3: Summary of antenna interface requirements
