Our goal is to design different Vivaldi antennas with simple, small, and low cost. They can be used in Ku frequency band, which can be used for brain tumor detection in the presence of abnormal tissues or tumor. The whole work is divided by two parts, antenna design part and brain tumor detection part. The antenna is being designed to work properly across the given Ku frequency 13.5 GHz to 14.71GHz. For tumor detection, a multilayer brain model (skin, fat, bone and white matter) is designed using the CST microwave studio. Basically, the antenna is placed between the skull and white matter of brain model to radiate into brain tissues. We analyzed the return loss and 3dB point to ensure the presence of brain tumor. The measured specific absorption rate shows that it is within the patient safety range.