Without matching circuits, performance of the antenna at 2.45 GHz is good, as shown in figure (a).  With matching circuits, shown in figure (b), the Return Loss is enhanced (meaning improved VSWR) and the Bandwidth is broadened – both of which are key parameters in improving the overall gain performance of the antenna over the desired frequency.  Note that the matching circuit component values will be different in every application depending on PCB material, thickness, and the factors mentioned earlier.  The values shown are for the Johanson test boards and are good starting values for finding the optimum values for an individual application.