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25 May 2018

Linx warns of antenna design costs for small volume shipments

Speaking at LPWA London, Linx Technologies’ President, Tolga Latif, outlined the problems that specialist antenna design can create when building an IoT device. Of course, Linx is on hand to sell both its antennae and provide advice to such customers, but for the LPWAN market, which is so full of startups, there are big decisions to be made.

Noting that most customers had no PCB experience, Latif explained that the simplest option for a customer that needs to add an antenna to their connectivity module is to use an external antenna. However, these are much more expensive than a specially designed internal embedded antenna – typically $10 compared to $2.

But here’s the rub – you have to have the necessary RF skills to design such antennae, and if you don’t, you will need to outsource that design. That can easily cost you $50,000, if you don’t have the RF skills in-house, and so there’s a balancing act to consider. Such customers then have to ask if they are going to see a return on their upfront investment, or if it is easier to just stick with the external antenna.

Latif noted that when modules can now cost around $7, as is the case with Verizon’s new ThingSpace offerings, adding $10 to that cost is quite a big step up. It is also one that is compounded when you factor in all the additional parts of a device, such as the battery, enclosure, and storage – and Latif recalled a Link Labs study that said the module cost alone was only around 5% of the cost of implementing an IoT design.

The Linx President also pointed to the other end of the spectrum – a dirt-cheap $0.20c spring that could be used as an antenna for a LoRa device, in which the antenna is tuned for specific bands simply by cutting it the required length. However, such an approach will only work for IoT networks that use a single radio band – and there aren’t many of those in the world.

So the simplest external antenna’s datasheet is around two pages, with those specialist internal designs requiring around ten times as many pages, according to Latif, providing a sense of the complexity and skills needed to make them work. Of course, for large shipments, that specialist design is going to pay off, but for many projects, an external antenna will suffice. There are numbers to crunch for such decision makers.

Put simply, Latif warned that having to support more frequency bands would mean bigger costs for the little guy. Single band designs are key for low costs, and so things like LoRa and Sigfox, which can use that single band function, appear to have an advantage in this regard, compared to NB-IoT and LTE-M.

The licensed LPWAN technologies are most frequently used in LTE band 8, according to Linx, although bands 28 and 3 are also common. NB-IoT is typically used in the guard-band space between bands, the air that keeps the bands from bleeding into each other, but again, this doesn’t suit that single-band ethos.

In time, there might emerge a pre-integrated antenna design that could enjoy the economies of scale that NB-IoT seems to be enjoying, which then might drive down the relative cost of supporting multi-band networks compared to single bands. In the licensed cellular world, it would be extremely difficult to get all the different MNOs to agree on a single band to use for LTE-M and NB-IoT, and so multi-band support is almost certainly going to be the way of life going forward.

Finishing his presentation, Latif explained that of the 300m smartphones sold in the US last year, there were probably around 100 separate designs that needed wireless certification. If estimates for 600m IoT devices are accurate, there would likely be 25,000+ designs that would need certification. Consequently, Latif suggests that the certification industry is probably a good investment opportunity.

The typical Linx customer orders between 1,000 and 30,000 units per year, but its largest customer orders a million annually. Its antennae are used in most LPWAN dev kits, giving it a nice way in for the sales team when it comes time for a startup to scale. Of course, the question of simple external or specialist internal then needs to be asked.