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28


DEVICES


ISSUE 03 2014


Probably the biggest challenge with LTE is the large number of bands that are supported, compounded by the support of legacy protocols


elements need to be well isolated. When the elements are small and closely spaced, coupling is an inherent issue that needs to be addressed. Again, this is an ideal simulation test case whereby various configurations can be compared to find optimum element spacing or orientation.


To go with present day typical handsets (115x60x10mm), EMSS designed a dual-port ESA with symmetry in this novel design, which keeps the antenna characteristics identical for both radiating elements


Taoglas: LTE is specifically designed around the principle that there are 2x2 MIMO (two antennas for both input and output). For the US market, for example, you now need to have enough space for two 700MHz antennas in a product that probably was not big enough to have one antenna in a small form factor. Now you need to have two antennas to have proper MIMO performance, the antennas need to be physically at a distance apart, but also their radiation patterns must not overlap, and that’s something that’s extremely challenging. It can be done with careful attention to detail, but having 2x2 MIMO on a small product the size of an iPhone and still achieving M2M device performance is very challenging. M2M devices, historically, are low data rate devices, so most have no need for the high speed that LTE brings. M2M manufacturers say ‘this device needs to be LTE for longevity reasons so it will work in the next 15 years, because we are scared that the older protocols (2G and 3G) are going to be shut down’. The repercussion of moving to LTE is that you have to spend a lot more money … and you need two antennas.


your product. And that’s a problem for antenna manufacturers like ourselves, because you can put out the best antenna in the world, but if the device manufacturer does not nail the rest of the device development issues such as Total Isotropic Sensitivity (TIS) and Radiated Spurious Emissions (RSE), in particular, then they will not reach certification, nobody will buy the product and no one will make any money. That’s such a big problem that we’ve gone as far as adding antenna integration consulting services to our offering – we need to get our customers through certification because this process is really hard.


Does LTE introduce new and specific challenges for the design and development of internal antennas for the latest LTE devices? EMSS: Probably the biggest challenge with LTE is the large number of bands that are supported, compounded by the support of legacy protocols. Furthermore, the support for MIMO (multiple input multiple output) has introduced new challenges: in order to achieve good MIMO performance


Can all specific LTE challenges be overcome or are some more stubborn than others? Does this call into question the migration to LTE? Taoglas: Yes, challenges can be overcome but the single biggest question about LTE migration is its costs. Whether GPRS, or 1xRTT, 2G solutions are perfectly sufficient for most M2M communication applications and are really cheap. The problem is that customers, especially infrastructure power companies such as automatic meter reading players, are terrified that they are going to deploy thousands of devices with GPRS only for the carrier to come back and tell them to upgrade all their devices to LTE. In the US, the single largest GSM carrier has said they will shut off the 2G network in the next few years, which means that 2G devices will stop working. That’s what pushes companies to put LTE into M2M applications. However, it does mean you start talking about five times the cost for the radio modules and antennas, because they are more elaborate and you need more physical space to implement them.


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