JODY-W2 - System integration manual
UBX-18068879 - R14
Design-in
Page 24 of 84
C1 - Public
summarizes the requirements for the antenna RF interface while
additional requirements for dual antenna design implementation.
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 and Bluetooth.
For 802.11a/n/ac.
Return loss
S
11
< -10 dB (VSWR < 2:1) recommended
S
11
< -6 dB (VSWR < 3:1) acceptable
The Return loss or the S
11
, 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
The radiation efficiency is the ratio of the
radiated power to the power delivered to
antenna input: the efficiency is a measure of
how well an antenna receives or transmits.
Maximum gain
The maximum antenna gain must not exceed
the value specified in type approval
documentation to comply with regulatory
agencies radiation exposure limits.
Table 16: Summary of antenna interface requirements
Item
Requirements
Remarks
Isolation
(in-band)
S
21
> 30 dB recommended
The antenna-to-antenna isolation is the S
21
parameter
between the two antennas in the band of operation.
Lower isolation might be acceptable depending on use-
case scenario and performance requirements.
Isolation
(out-of-band)
S
21
> 35 dB recommended
S
21
> 30 dB acceptable
Out-of-band isolation is evaluated in the band of the
aggressor to ensure that the transmitting signal from the
other radio is sufficiently attenuated by the receiving
antenna to avoid saturation and intermodulation effect at
the receiver’s port
.
Table 17: Summary of Wi-Fi/Bluetooth coexistence requirements
⚠
In dual antenna configuration, a good isolation is critical to achieve optimal throughput
performance in Wi-Fi/Bluetooth coexistence mode while operating in the same 2.4 GHz band.
In both the cases, while selecting external or internal antennas, observe the following
recommendations:
•
Select antennas that provide an optimal return loss (or VSWR) over all operating frequencies.
•
Select antennas that provide optimal efficiency figure over all operating frequencies.
•
Select antennas that provide appropriate gain not to exceed the regulatory limits specified in some
countries like the FCC in the United States.
A method to design for antenna micro-strip evaluation is to place an U.FL connector close to the
embedded PCB or chip Antenna. The UFL connector needs only to be mounted on units used for
verification.
