2.4GHz Antenna Ground Plane

ACharnley said:

I've a bluetooth antenna inside a metal enclosure

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An antenna inside a metal enclosure sounds very bad.
The metal enclosure will act as a faraday cage and greatly attenuate the signals to and from the antenna.

ACharnley said:

Would I be correct in saying if I wanted the antenna to radiate 180degree and not 360 degree then I should install some copper behind the antenna to reflect the signal and increase efficiency in that direction?

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Putting a groundplane on the other side of the circuit board from the antenna trace will badly affect the resonant frequency of the antenna and attenuate signals to and from the antenna.

Your groundplane should be in the opposite direction from the antenna feed point and not close up to the antenna radiating element.

JimB

Sorry I should have written that better - the antenna is on the side of a metal enclosure. There's a large hole and the PCB covers it. Thus 50% of the signal will be going into the case, which is why I wondered if placing a copper plane behind the antenna (not connected to ground or the antenna) acts to reflect this 50%.

I also noticed the antenna has a via, which isn't connected to anything.