Metamaterials in Patch Antenna

I have uploaded a pic for this question just for an example......

1> I want to know in detail why and how the double negative property (-ε,-μ) of DNG metamaterials can enhance the radiation,gain and bandwidth of a patch antenna?

2>Also can anyone explain what is the "side-grounds" (the two metallic square patches on both sides of the microstrip feed line)in the picture and what is its function?

Thanks....