I've not had cause to look on a saloon for one, but it has to be located
within a half a metre or so of the antenna screen printed on the window (if
that is the antenna type you have on your model).
Take a look behind the trim located on the "C" pillar (the support for
the roof between the rear window and the rear door) BMW has often
hidden it there - the closer it is to the antenna on the glass the
better it works.
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