With the aid of external circuits, matching the antenna to a 50 ohm impedance optimizes the performance and the response at the operating frequency bandwidth by maximizing power transfer to the antenna on the board.  For example, the reference matching circuit components are shown for the Johanson model 2450AT45A100 2.45 GHz chip antenna.  The recommended values, according to the Johanson spec sheet for this particular model, include a 1.5 pF series capacitor and a 3.9nH shunt inductor.