nrf52 antenna impedance

[vea45]

Hi,

I'm designing an antenna for the NRF52 but with some different conditions, the antenna will be under a silicone superstrate and this will change the impedance of the antenna extracted from your designs... What is the best way to deal with it?

I know that the antenna frecuency will decrease since the dielectric constant is higher than air so it will be necessary to design a higher frecuency antenna. Actually it's a PIFA antenna...

Also I don't know if I could change the reference values of C3 (0.8pF) and L1(3.9nH) to adjust those values to the new situation.

Thank you in advance.

[mstrouse]

Do you have access to a VNA (vector network analyzer)? Using the VNA, measure the antenna in-situ and tweak the matching components to suit. And except for using a high-end microwave software simulation tool (that can also accurately simulate the silicone), the VNA route is your best bet. [EDIT] See this for information on how to do this - infocenter.nordicsemi.com/.../nwp_017.pdf

Another (sloppy) alternative is ... you could use a spectrum analyzer and measure the frequency / output power (and harmonics!) as you adjust the component values. Ugly, but it could get you close. [EDIT] See this to get an idea on how to do this (example using nRF24L01) - infocenter.nordicsemi.com/.../nwp_013.pdf

[vea45]

Yes I have access to an VNA but I can't calibrate it... I read those papers but I want to know if it's possible to change the values fof C3 and L1 so I could tune the pi network... (I added a shunt component to complete the network). Also I used CST to do a simulation of my situation but the measured results and the simulated ones are quite diferent...