Wireless Technologies
Developing an Effective Antenna
for IoT Applications
AMatt McWhinney, Molex ccess to the internet is no longer restricted to devices intended
for people; things that we may never interact with
directly now account for billions of connections and that
number is only going up. As vehicles become more connected,
we will see increased demand for V2X solutions, the rollout of
5G services will allow even more connectivity, while locationbased
services are increasing demand for GPS and GNSS
functionality. All of these applications rely on wireless communications
and, in many cases, they will be hidden from sight,
located deep within large machines, vehicles or even structures
like bridges.
The data that these things produce is increasingly missioncritical
and so developing robust devices able to maintain a
connection under sometimes difficult conditions is even more
important. With an increasing number of System-on-Chip
(SoC) and System-in-Package (SiP) devices available with fully
integrated RF interfaces, accessing wireless connectivity is now
simpler than ever, however there is one aspect that still needs
special consideration to achieve optimum performance; the
antenna.
Link budgets are critical in delivering reliable communications
and perhaps the single most important part of developing
an RF interface. The antenna selection and, more crucially, the
way it is designed into the system will have a major influence on
the link budget. Because of this, understanding and following
well established RF antenna guidelines forms an important part
of the overall design process.
Figure 1: RF is now used in more applications, driving the
development of protocols to meet the needs of specific
application types
The basics of antenna theory
We now experience many forms of wireless connectivity in our
digital lives, with little consideration for the antenna used, but
they are clearly the single most influential component in an RF
system.
In theory, any conductive wire can be an antenna, as it will
be capable of radiating and receiving RF energy through the air.
However, in order to do this reliably it is necessary to take this
theory and apply engineering know-how. The challenge many
Figure 2: Antennas come in a various shapes, sizes and
materials. Choosing the right one isn’t always simple
design engineers face today is how to achieve this optimal design
without the benefit of a full understanding of the nuances
of RF design.
The first thing to appreciate is that antennas are indiscriminate,
by which we mean they do not really care what the energy
(signal or protocol) contains, they are merely concerned with its
presence (frequency) and levels (strength). It is the modulation
scheme that carries the real data and in order for the backend
to recover this it is important that the antenna is designed in
sympathy with this. In fact, an antenna will behave in exactly
the same way when it is both receiving and transmitting; known
as the theory of reciprocity. Of course, this also means that it
doesn’t really matter if the device is a transmitter, a receiver or
both, the antenna design will be the same.
In terms of the devices typically being deployed as part of
the IoT, an antenna will be classed as either embedded, meaning
it would be mounted directly on the PCB and connected
using copper tracks, or cabled, which means it is connected to
the PCB using a (normally coaxial) cable. Cabled antennas are
often mounted inside the enclosure, but of course, antennas
may also be mounted outside the main enclosure or, in some
cases, on the outside of a building.
As part of the antenna design or selection it is relevant to
consider several criteria, including the data rate needed, the
frequencies being used and range of the wireless connection,
which will impact the system power levels. Many of these criteria
will be common across a range of applications and so it is
not surprising to know that they are already defined in specifications
for wireless protocols, such as Bluetooth, Wi-Fi, LoRa and
many others targeting the IoT and various other applications,
such as wireless networking and remote metering.
Range is perhaps the most basic parameter that can help
when determining the most appropriate protocol for a given
application. This will cover short, medium and long range, spanning
less than 10cm to many kilometres, respectively. Range is
also closely related to data rate and this can often be a bigger
determining factor than range, although of course the two are
both largely dependent on power. Some protocols support only
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