The present invention generally relates to cellular phones having multiple antennas. The invention relates to how two antennas in a diversity or MIMO antenna system interact through mutual coupling. The mutual coupling is due to proximity of the two antennas, their antenna pattern and efficiency. The performance of the system can be optimized by adjusting the mutual coupling between the antennas. The primary and secondary antennas can be "tuned" and "de-tuned" respectively to enhance system performance. In this invention, the primary and secondary antennas are tuned independently using MEMS capacitor configured in the antenna aperture for frequency tuning.