Developing an effective antenna for IoT applications
The data that these things produce is increasingly mission-critical 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.
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 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 very low data rates but over long distances and at relatively low power levels, while higher data rates are typically restricted to shorter distances but may still require more system power to function.
Operating frequency is also defined by the protocol and most engineers will be at least somewhat familiar with the license-free bands allocated for Industrial, Scientific and Medical (ISM) applications and, within these, the 2.4-GHz band used by many of the most popular protocols. Despite using the same part of the spectrum, these protocols offer various ranges and data rates, which influences both their relative power requirements and the overall cost of radio devices. It is important to realise that the RF electronic circuitry defines the protocol, whereas the antenna simply receives and transmits RF signals fed to it by the electronics, irrespective of the protocol used.
This means that while the RF SoC/SiP used may differ between protocols, it is actually possible to use the same antenna design for any protocols that operate at the antenna’s intended frequency, such as those operating at 2.4 GHz (WiFi, Bluetooth, Zigbee, etc.). This means, of course, that one antenna can support several protocols. Having said that, there remain other relevant considerations when selecting an antenna, such as the physical space available and its location within the product. This will define the shape of the antenna, which may need to conform to a given profile in order to support the required frequency or bandwidth.
Antenna design expertise
Molex has been designing, manufacturing and supplying standard and custom integrated antennas for two decades, for mobile and IoT applications in various volumes and for leading device manufacturers around the world.
The Molex antenna product portfolio covers all the major protocols used today, as well as proprietary solutions, with a focus on embedded (PCB mounted) and internal cabled antennas, when performance requirements may dictate their use.
Embedded antennas can be extremely small and manufactured from ceramic and plastic, as well as stamped metal, weighing just a few grams (Figure 4). Cabled antennas can be made using PCBs, both rigid (FR4) and flexible, as well as stamped metal. These capabilities make it simple to find the most appropriate antenna design, whatever the application. Even though they can be made very small and compact, embedded antennas still come with design requirements that, if followed, will help ensure that the antenna performs as the specification demands. Many factors, such as the size of the PCB, its shape and where the antenna is mounted on the PCB can all impact how the antenna performs.
To support the product portfolio, Molex has produced a library of application specifications. These are engineering documents that go beyond the standard antenna data sheet. They include not only performance information but a reference design, with advice on where and how to locate the antenna on a PCB. Perhaps most importantly, the application specification provides an estimate of the antenna’s operation and how this will vary based on its location on a PCB, taking into account its proximity to other components and features such as batteries, metal shields and the cable itself for cabled antennas. These application specification documents provide essential guidelines that system designers should read to understand how to best engineer the antenna into each system.
In most cases, the information provided in the application specification has been simplified to make it more easily accessible to engineers with varying levels of RF expertise, and of course Molex can also provide access to an expert if and when required. In many instances, it is advised that design teams placing antennas into their systems seek assistance and guidance from an RF expert. This can save time when it comes to understanding what additional measures are needed to boost antenna performance and quantitatively measuring antenna performance in a system.
To support its customers, Molex has also invested in antenna measurement technology, including field-scanning chambers to support product development, up to frequencies used in 5G transmissions. When used alongside its advanced simulation capabilities, this enables Molex to develop antennas that deliver high performance while still complying with SAR (Specific Absorption Rate) specifications. Once designed, Molex can also manufacture custom antennas, to meet the customer’s production needs. Molex not only designs antennas; its RF engineers are experts and are ready to assist customers’ design engineers investigate and document the performance of antennas in a system. If your application requires improved RF performance, consider turning to a Molex RF expert for assistance.
If you enjoyed this article, you will like the following ones: don't miss them by subscribing to :
