ANNA-B4 series - System integration manual
UBX-21000517 - R03
Contents
Page 23 of 74
C1-Public
•
RF section may be affected by noise sources like hi-speed digital buses. Avoid placing the antenna
close to high buses or consider taking specific countermeasures like metal shields or ferrite sheets
to reduce the interference.
•
External antennas, such as linear monopole antennas:
o
Choose a module integration that supports an external antenna if the product includes a metal
product enclosure.
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.
⚠
Take care of interaction between co-located RF systems like LTE sidebands on 2.4 GHz band.
Transmitted power may interfere or disturb the performance of the module.
⚠
To avoid invalidating the compliance and pre-certification of u-blox modules with the various
regulatory bodies, use only external antennas included in the
Reference design source files are available from u-blox on request.
3.3
Antenna connected through the RF pin
Follow the guidelines when selecting either an external antenna or an internal antenna mounted on
the main PCB.
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 Antenna 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.
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 7
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.
Although higher gain antennas can be used, these must be
evaluated and/or certified. See also
Table 12: Summary of antenna interface (ANT) requirements
When selecting antennas, the following recommendations should be observed:
•
Select antennas that provide optimal return loss (or VSWR) over all operating frequencies.
•
Select antennas that provide optimal efficiency over all operating frequencies.
•
Select antennas that provide an appropriate gain (that is, combined antenna directivity and
efficiency), so that the electromagnetic field radiation intensity does not exceed the regulatory
limits specified in some countries (like the FCC in the United States for example).