In this work, breast tumor conditions in human body are detected by simulation of rectangular micro-strip patch antennas at 1.8 THz. The S-parameter, Voltage Standing Wave Ratio (VSWR), and radiation pattern of the designed antenna can be used to identify the existence of a breast tumor. Initially, a rectangular micro-strip patch antenna is designed, simulated, and the associated antenna properties are measured without tumor. In the absence of a tumor conditions, the resonant frequency occurs at 1.793 THz. The resonance under tumor conditions is obtained at 1.8 THz. Next, the impacts of several factors on the breast phantom setup are examined, including melanoma and water molecules. Observed variation in the resonant frequency indicates a 5 GHz frequency shift. This antenna can identify microscopic malignant tumors that are bigger than or equal to 1 mm within the breast phantom. Other factors like VSWR and radiation pattern under transmit and receive antenna configurations are also evaluated to measure the efficiency of the antenna constructed at Terahertz frequency. Preliminary findings indicate that the antenna can identify the existence of tumors with a variety of impacts, including distinct tumor radii, the presence of a melanoma layer, and the presence of water molecules in the breast tissue.