add a second antenna
No. That chip (like most) only uses a single antenna. If you added a 2nd antenna and somehow combined their signals (in the RF domain), you might improve performance in a specific direction, but you are also going to get nulls where the 2 antennas both pick up a signal and the phases are such that they cancel.

You'd really need a 2nd RF amplifier &amp; demodulator. Alternatively just use 2 of those CSR 8635 ?