This paper is all about to design an antenna for brain tumor detection using a novel material Kapton polyimide. A brain tumor, which has the potential to spread throughout the body and result in cancer, is one of the worst disorders. Using a novel material and observing variation in the S1,1 parameter to spot brain cancers is the main objective of this paper. An on-body microstrip patch antenna constructed in the K band and a three-size brain tumor in a brain phantom model were employed to identify the existence of brain tumor. This antenna can operate between 4 and 14 GHz. The resonance frequency of the proposed antenna was discovered to be 12.96 GHz in free space. A VSWR of 1.00 and −92.06 dB S1,1 was also measured in this area. S1,1 is −49.93 dB at 8.58 GHz in the Normal Brain and −40.51 dB at 11.87 GHz in the Tumor Affected Brain.