Investigation of Breast Tumor Size Effects for Microwave Breast Imaging with Ultra-Wideband Microstrip Antenna

Breast cancer is the most common invasive cancer in women and a leading cause of cancer-related deaths worldwide. Tumor size plays a crucial role in diagnosis and staging. This study investigates the impact of tumor size on the $\mathbf{S 2 1}$ transmission signal and specific absorption rate (SAR) distribution in a 3D breast model simulated in COMSOL Multiphysics using an ultra-wideband (UWB) microstrip antenna. The results show that energy concentration increases with tumor size, with larger tumors showing broader SAR distributions. At a frequency of 3.1 GHz, an inverse relationship between SAR and $S 21$ is observed; smaller tumors exhibit lower SAR values and stronger S21 signals, while larger tumors demonstrate higher SAR values and reduced S21 signals.