Electronics > RF, Microwave, Ham Radio

BLE Antenna impedance matching

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ivonenand:
Hi guys,
I'm looking for a small Bluetooth 2.4Ghz SMD antenna and I came across a part from Wurth Elektronik, part no. 7488960245. The Antenna is specified to have a 50 Ohm impedance, great.



However, one page below in the datasheet, there is a typical connection diagram, which includes an impedance matching circuit made of a 1.2pF capacitor and 2.2nH inductor.



There's even a PCB example, where if you enter with a 50 Ohm line, you go through the matching circuit first, and then to the antenna.



Now here's what's confusing me. If the feed/input impedance is 50 Ohms and the Antenna impedance is also 50 Ohms, why do you need an impedance matching circuit?

Thanks for any input on this topic,
Regards,
Ivo

E Kafeman:
Correct, no need for matching if feed to antenna and antenna is conjugate matched.
IRL does it never happen.
 Transmission line is not ideal and TX/RX radio impedance is neither ideal 50 Ohm.
  Antenna real impedance is an factor of its nearfield environment. Ground size and enclosure dielectric properties will affect antenna impedance.
 Big enough ground area and length is even more critical for selected type of short quarterwave ceramic antenna, which needs to be mirrored in ground with low losses to create a full halfwave antenna without to much losses and less efficiency.
That is why by Wurth provided PCB example have a rather big ground area at 2.4GHz, to achieve decent measured antenna efficiency, bandwidth and for simpler tuning.

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