LILY-W1 series - System integration manual
UBX-15027600 - R09
Design-in
Page 20 of 64
C1 - Public
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A de-facto standard for SMA connectors implies the usage of reverse polarity connectors (RP-
SMA) on end-user accessible Wi-Fi interfaces to increase the difficulty to replace the antenna
with higher gain versions and exceed regulatory limits.
The following recommendations apply for proper layout of the connector:
•
Strictly follow the connector manufacturer’s recommended layout. Some examples are provided
below:
o
SMA Pin-Through-Hole connectors require GND keep-out (that is, clearance, a void
area) on all the layers around the central pin up to annular pins of the four GND posts.
o
U.FL surface mounted connectors require no conductive traces (that is, clearance, a
void area) in the area below the connector between the GND land pins.
•
In case of connector’s RF pin size wider than the micro strip, remove the GND layer beneath the
RF connector to minimize the stray capacitance thus keeping the RF line 50
Ω
. For example, the
active pin of UF.L connector must have a GND keep-out (also called “void area”) at least on the first
inner layer to reduce parasitic capacitance to ground.
2.2.2.2
Integrated antenna design
If integrated antennas are used, the transmission line is terminated by the antennas themselves.
Follow the guidelines mentioned below:
•
The antenna design process should start together with the mechanical design of the product. PCB
mock-ups are useful in estimating overall efficiency and radiation path of the intended design
during early development stages.
•
Use antennas designed by an antenna manufacturer providing the best possible return loss (or
VSWR).
•
Provide a ground plane large enough according to the related integrated antenna requirements.
The ground plane of the application PCB may be reduced down to a minimum size that must be
similar to one quarter of wavelength of the minimum frequency that has to be radiated, however
overall antenna efficiency may benefit from larger ground planes. Proper placement of the
antenna and its surroundings is also critical for antenna performance. Avoid placing the antenna
close to conductive or RF-absorbing parts such as metal objects or ferrite sheets as they may
absorb part of the radiated power, shift the resonant frequency of the antenna or affect the
antenna radiation pattern.
•
It is highly recommended to strictly follow the specific guidelines provided by the antenna
manufacturer regarding correct installation and deployment of the antenna system, including
PCB layout and matching circuitry.
•
Further to the custom PCB and product restrictions, antennas may require tuning/matching to
reach the target performance. It is recommended to plan measurement and validation activities
with the antenna manufacturer before releasing the end-product to manufacturing.
•
The receiver section may be affected by noise sources like hi-speed digital busses. Avoid placing
the antenna close to busses as DDR or consider taking specific countermeasures like metal
shields or ferrite sheets to reduce the interference.
•
Take care of interaction between co-located RF systems like LTE sidebands on 2.4GHz band.
Transmitted power may interact or disturb the performance of LILY-W1 modules where specific
LTE filter is not present (LILY-W131).
2.2.2.3
LTE coexistence filter selection
LILY-W131 does not include a band pass filter specifically designed to allow Wi-Fi coexistence with
LTE-band7 modems. If a dedicated LTE filter is required on LILY-W131, the designer can refer to
Table 13 for a list of recommended filters or consider parts with similar performance.
Manufacturer
Series
Part number
Remarks