WIRELESS & IoT
other components – its performance may be very different in real life even if the design is generally ‘correct’. The best way to determine the operational range for the device is to carry out RF tests in an anechoic chamber. An antenna in noisy environments will
inevitably draw more power than devices operating in controlled spaces, and the amount of data transmitted is directly related to the battery life. Ideally the battery needs to be large enough to keep a device operating for a reasonable period of time, with an easy way to replace or recharge it. Integration example - Chip antenna in a
wearable design – the antenna is the part labelled SRCW004 in figure 1.
Flexible antenna integration example A flexible antenna is still embedded, but can be mounted in a different position within the product design. FPC antennas can be fixed to the underside
of your product housing with a cable and a connector carefully routed to the PCB. The antennas are more expensive due to the cable and connector, but they can perform better in some applications because the antenna is now away from the main host PCB where other components might cause noise and interference. However the position of the FPC antenna and the cable routing are
still critical to the design because the cable actually becomes a part of the antenna in operation. Figure 2: Integration example – a flexible
antenna “Asper” folded and inserted within a camera design
4G / LTE designs and certification The 4G/LTE frequencies used for cloud-based remote monitoring applications add two more design challenges – ground plane size and certifications. 4G frequencies in the US are as low as 698MHz, or even 617MHz if you use the new T-Mobile B71 band, and at frequencies below 1GHz, SMD antennas require a minimum of 100mm of ground. Yet many IoT devices today are around 50mm in length or smaller. Also, the design will need to pass accreditation tests as well. If there is not enough space for a ground
plane of 100mm, there are some RF solutions. Maybe the copper ground can be extended, or the antenna might be tuned to use certain bands of operation, to obtain good performance without noise or spurious emissions. The second challenge is to pass
certification. Designs for the cellular networks have to pass strict tests before they can be certified for use on the carrier networks, and these are different for each country and each mobile network. In the US, the FCC also
sets standards which wireless devices must pass before they can be sold on the US market. Europe’s equivalent is the CE test, and the UK will have its own UKCA tests to replace CE from 31st December 2021. Europe also has the RED (Radio Equipment Directive) tests. In the US all wireless devices must pass
PTCRB testing as well. These tests apply to all mobile and IoT devices and ensure that the device is compliant with the carrier network. This means that all designs for the 4G/ LTE networks should be tested to reveal any issues with the RF performance before the design is finalised, to uncover any issues that might require modifications to the design. The four key tests are for Total Radiated
Power (TRP), Total Isotropic Sensitivity (TIS), Radiated Spurious Emissions (RSE) and Specific Absorption Rate (SAR). SAR is needed for RF devices that will be used within 20cms of the human head or body. All of these can be carried out in an anechoic test chamber and are generally done as a precursor to certification, to assess device readiness, and prepare for the final stage of gaining certification for the product. For more information and a useful free antenna placement tool visit:
antenova
www.antenova.com
Figure 2: Camera integration
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