Can we feed one antenna with two different frequency signals at a time......No right..... It needs some time to finish that pulse......Same thing we can not use it at a time........
After one frequency signal (one or multiple cycles) is applied then another frequency signal can be feeded.
If it is an antenna that works at two frequency bands at the same time then you can use it to transmit data at both bands at the same time. If it is tuneable between bands then you can't use both bands at once.