We got 6.9dB gain and 7.1dBi directivity for this structure.
Rad. efficiency is 95.7% (-0.1872dB), which is 3% higher than that of the antenna without DR loading.
Then I studied all antenna parameters by increasing the height of the substrate to 2mm and keeping whole remaining
structure same as it was with h=0.8mm. There is further improvement in BW and rad. efficiency, while all other