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.

[MartinBL]

Hi

It is very difficult to give any general advice here. Any antenna would somehow be affected by a human body. The best thing for you to do is to create a MyPage account and open a support ticket there. Then we can do a confidential review of your project and possibly give you more solid advices.

[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.

[Dave_couling]

As for bandwidth, you want a wide bandwidth antenna. Each human body will shift the Antenna differently. Having a wide bandwidth will assure that the antenna response will be within the BLE frequency range.

Inverted F trace antennas have quite good bandwidth and are a good option for this application. Much better then 99% of chip antennas. However chip antenna's can be more immune to human body detuning.

In summary, a good trace antenna (Inverted F) that is tuned properly in its application environment (on Human Body) can have good performance.

[tamojit]

Please can you post a review of my design at this thread???
Please help me as I have just started learning about antenna designing.