NINA-B4 series - System integration manual
UBX-19052230 - R09
Design-in
Page 22 of 61
C1-Public
2.6.1
External antenna selection
Designers are encouraged to consider one of the u-blox certified antennas and follow the layout
requirements outlined below:
•
External antennas, such as linear monopole antennas:
o
External antennas do not impose any physical restrictions on the design of the PCB where the
module is mounted.
o
Radiation performance depends mostly on the type of antenna used in the application product.
Choose antennas that provide an optimal radiating performance in each operating band.
o
RF cables must be carefully selected to keep insertion losses to an absolute minimum. Low-
quality or long cables introduce additional insertion losses. Large insertion losses reduce the
radiation performance.
o
A high quality 50
coaxial connector provides proper PCB-to-RF-cable transition.
•
Integrated antennas, such as patch-like antennas:
o
Internal integrated antennas impose physical restrictions on the PCB design:
An integrated antenna excites RF currents on its counterpoise, typically in the PCB ground
plane of the device that effectively becomes part of the antenna. Consequently, the
dimensions of the ground plane define the minimum frequency that can be radiated. To
optimize radiation, the ground plane can be reduced to a minimum size that should not be less
than a quarter of the wavelength frequency that needs to be radiated. The orientation of the
ground plane related to the antenna element must be considered.
The RF isolation between antennas in the system must be as high as possible, and the
correlation between the 3D radiation patterns of the antennas must be as low as possible. In
general, an RF separation of at least a quarter wavelength between the two antennas is a
minimal requirement for achieving isolation and pattern correlation. Consider increasing the
separation to maximize performance
–
if possible.
As a numerical example, consider the following physical restrictions of the PCB design:
Frequency = 2.4 GHz
→
Wavelength = 12.5 cm
→
Quarter wavelength = 3.125 cm
1
o
Radiation performance depends on the antenna system design, the mechanical design of the
final product, and the application use case. Choose antennas that offer optimal radiating
performance in the operating bands and meet the mechanical specifications of the PCB and
entire product application.
summarizes the RF interface requirements of the antenna.
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.
1
Wavelength referred to a signal propagating in air