Page 30 - EE Times Europe Magazine | June2020

30 EE|Times EUROPE

How to Get Better Wireless Performance for Mobile Devices with Small PCBs

for a 3G/4G chip antenna operating at frequencies of 791–960 MHz,
1,710–2,170 MHz, 2,300–1,400 MHz, and 2,500–2,969 MHz.
Generally, the ground plane would need to be 100 mm or more for a
device using the frequencies below 1 GHz. In the U.S., the 4G frequen-
cies use bands as low as 698 MHz or even 617 MHz, as with T-Mobile’s
B71 band, requiring a ground plane even longer than 100 mm.

POSITIONING THE ANTENNA ON ITS PCB
Next, we should consider the position of the antenna on the PCB and
its placement in relation to other components. The antenna should be
placed in the best position in the overall RF layout and PCB stackup to
allow it to radiate effectively.
Each individual antenna is designed to work efficiently in a few
places on a PCB. This is often the corner or an edge; however, each
antenna is different, so it is important to select an antenna that fits
into the design and place it according to the manufacturer’s recom- Figure 4 (Image: Antenova Ltd.)
mendation for that antenna.
Figure 2 shows how the antenna is placed with its clearance area in OVERALL RF LAYOUT AND PCB STACKUP
a small device such as a wearable product or watch. Figure 3 shows a You can maximize the performance of the antenna by giving careful
suitable antenna placement for a watch design. The design maintains consideration to the layout of the RF elements in the design. The
the recommended clearance specified above and below this antenna, copper ground plane should not be cut up with traces or arranged over
which is shown in red. more than one layer; then the ground plane portion of the antenna will
be able to radiate more effectively.
It is essential to keep components such as LCDs or batteries clear
of the antenna area in the PCB layout, as these can interfere with the
way the antenna will radiate. For multiband frequencies, we suggest a
PCB layout with a minimum of four layers. Figure 4 shows how the top
and bottom layers provide ground planes, while the digital signals and
power, which need to be away from the ground plane, run in the space
between these.

TUNING THE ANTENNA FOR PERFORMANCE
For those cases in which the ground plane is shorter than ideal, a
designer can look at other techniques to increase the performance of
an embedded antenna.
One way is to tune the antenna for its country of operation. The 4G
Figure 2 (Image: Antenova Ltd.) frequency range is a wide one, spanning from 698 MHz to 2,690 MHz,
but each world region uses just a portion of this band, and an antenna
can operate on only one frequency at a time. This means that when
a product is to be used in one geographical region, it can be tuned to

Figure 3 (Image: Antenova Ltd.)

Do not place noisy components, such as a battery or an LCD, close
to the antenna section. Antennas are passive components that receive
energy and will pick up noise radiated from the noisy components and
transfer that noise to the radio, degrading the received signal. The
antenna should also be placed away from the human body to improve
RF performance; this is the distance marked in blue in Figure 3.
The arrangement of the RF feed and the ground connections are
critical to the function of the antenna. With small embedded anten-
nas in small PCBs, the copper tracks etched on the PCB may form an
integral part of the antenna, so care should be taken to follow the
manufacturer’s specification or reference design. Figure 5 (Image: Antenova Ltd.)

JUNE 2020 | www.eetimes.eu