antenna radiation and scattering

hi
what is the differences between resonant frequency for radiation in an antenna and resonance frequency for scattering (enhancement in radar cross section)
how can we explore it by reflection coefficient or s11
In many cases it says in resonant frequency of element we can see an enhancement in radar cross section
I can't distinct these
thanks a lot

the resonant frequency is dependent to the shape of the object. for a resonant antenna, the current on the input would resonance on the surface of the antenna. this is same for an object in the sky, but the input is not directly linked to any ports. as a result of the propagating wave, the surface currents would appear and resonance on the surface of the object. hence, it would radiate back better and the receiver would receive a far more powerful signal; so it is like the receiver has spotted a bigger object.