Antenna design for wearable nrf51822

[atb08]

Hi All,

I am currently working in a team desigining a wearable that uses BLE in 2.4 GHz band to communicate with smartphones and other devices. We have been working with an nrf51822 chip as our BLE controller coupled with a balun and chip antenna and have had mixed results thus far. As it is a wearable device that is worn close to the skin, we would be interested in knowing if a trace antenna would offer better performances? Especially as it would also provide a gain in terms of space.

Many thanks in advance, it has been a real pleasure using the devzone and provided documentation during the development process.

[Dave_couling]

When it comes to wearables there are two considerations for tuning: Tuning and Bandwidth. The human is going to affect the tuning and bandwidth of the Antenna, as well as absorb some of the RF radiation. There is not much you can do about the absorption other than try and place the antenna as far as possible from flesh.

However for the aforementioned two items; you need to tune your antenna with the product placed on Human Body as is your use-case. The human body will down-tune the center frequency of the Antenna Tuning. Meaning if the Antenna is normally tuned to be centered at 2.45GHz, place on a human body could shift it down to 2.35GHz. Thus you need to up-tune the antenna so that it shifts down to 2.45GHz instead.