Hi, svarun: I think your formulas are correct. Yes. In order to be wide band, we need to have less stored energy from the formula for Q. However, it does not mean we need to have smaller volume for it. From my experience, when the volume for the energy (not the total stored energy) is small, the antenna is always narrow band. When a small antenna has a wide bandwidth, its field normally spreaded into the surrounding area. As I mentioned, a slot antenna is like that. Even a slot antenna has low profile, however, its field and energy is not confined near the slot. It is spreaded into the surrounding much more than a microstrip antenna. Another example is EBG structure. It can make an antenna low profile while it can be much wider bandwidth than a microstrip antenna. However, please remember, its field and energy is spreaded horizontally. Much of the energy and field is spreaded into the region surrounding the patch in the horizontal location. If you change the structure not very far away from the patch in the horizontal location, you will see change in an EBG antenna's performance. It is a clear indication that much field and energy is there. The above are just from my observations. You may try to check whether it is true. Regards.