Antenna Design & Integration
In addition to the radio core, a wireless IoT device of any kind needs to have an antenna to be connected. The antenna can be internal or external, depending on the purpose or placement of the device. In general, external antennas provide better performance, but bring along specific challenges, especially for wearable devices. In such cases, internal antenna is usually a better choice and the antenna‘s design and integration are important factors for the performance of the IoT device.
Internal antennas can be commercial off-the-shelf (COTS) or custom built. Use of COTS antennas enables faster development without additional engineering effort but requires knowledge of the original antenna design and operating environment the antenna was designed for. This sets certain boundary conditions for antenna performance, not to mention other electronics that are built around the antenna. Depending on the case, the best possible antenna performance may be achieved with a custom-built antenna.
Wearable or embedded IoT devices are usually relatively small which poses challenges to the obtainable antenna performance. Such devices need an internal antenna, and it is usually thought of as only a small part of the device that can be placed wherever there is space left. Although the antenna is physically a small part of the device, challenges arise from the way the internal antenna works.
The internal antenna operates at certain allocated frequencies (translates to wavelength). Depending on the frequency, the antenna uses the electrical ground plane of the device as part of the radiating element i.e., the antenna. When the entire ground plane of the device acts as part of the antenna, the size of the device also limits the available antenna performance. The fact that the physical size of the product limits internal antenna performance can be optimized by utilizing antenna tuner concept. This means that the antenna matching component values are dynamically tuned depending on the instantaneous operating frequency.
In the case of wearable devices, the placement of the device and its internal antenna very close to the body brings its own challenges to the performance and optimization of the antenna. The antenna efficiency is heavily impacted as the human body attenuates radio waves. This reduction in antenna performance needs to be minimized during the design process to achieve the required wireless operation range for the device. However, an antenna inside a wearable device should also meet specific absorption rate (SAR) limits. The key is to have the right know-how from all the relevant aspects for achieving optimized antenna design.
In order to streamline the antenna design process to achieve the optimal results, antenna simulations should be started as soon as the first draft of the product concept is available. In some cases, antenna simulations are used already in defining this first product concept draft.