Breast cancer is one of the most prevalent cancers affecting women worldwide, with early detection significantly improving treatment outcomes and enhancing survival rates. This work aims to develop a simple, low-cost miniaturized mmWave imaging antenna for detecting breast tumors by monitoring changes in the antenna’s S11 parameter. The article explores the design of millimeter-wave antennas operating at a central frequency of 33 GHz, constructed on an RT/duroid 5880LZ substrate with a dielectric constant of 2.2, using the HFSS EM simulator. The proposed rectangular mmWave antenna has dimensions of 2.45 mm × 2.5 mm × 0.5 mm, offering substantial penetration capabilities. The simulation examines various scenarios, including breasts without tumors, breasts with tumors, and tumors in different positions. To establish a clearer connection between the alteration of S parameters and tumorous tissues, an S vector was generated. The results from the S11 parameter revealed the capability to detect the presence of tumors and their locations. The designed antenna resonated at 33 GHz with a return loss value of -19.33 dB, a satisfactory bandwidth of 2.10 GHz, a total peak gain of 7.07 dB, and a voltage standing wave ratio of 1.2. These results indicate that the proposed antenna is suitable for tumor detection and localization in breast cancer, as well as for fifthgeneration (5G) wireless communication applications