An antenna with a modified ground plane is proposed for modern mobile devices in the wireless communications. The proposed antenna design comprises a planar inverted‐F antenna with a feeding capacitor (CF) at the top side of the ground plane, and an additional closed loop with lumped inductors (L1 and L2) at the end of the ground plane. The closed loop is connected to the small ground plane for ground mode tuning so that the ground mode resonant frequency is equal to the operating frequency. In the simulation, the −10 dB bandwidth is 140 MHz (from 2.39 to 2.53 GHz) without the closed loop, and is 320 MHz (from 2.34 to 2.66 GHz) with the proposed closed loop. The measured efficiency is 61% on average from 2.3 to 2.6 GHz for the proposed antenna, and is 36% for the reference antenna. The ground mode resonance can be easily tuned, and the proposed technique is a versatile approach for antenna performance improvement.