Experimental validation of a dual-band slotted patch antenna for microwave brain tumor sensing

Microwave transmission sensing offers a compact and non-ionizing approach for investigating dielectric changes associated with biological tissue abnormalities. This study presents the experimental validation of a compact dual-band double-rectangular slotted microstrip patch antenna for controlled brain-tumor phantom sensing. The antenna has an overall dimension of 36 × 36 mm² and was designed in CST Microwave Studio to operate at 3.08 and 4.28 GHz. Two identical antennas were fabricated on FR-4 substrate and experimentally characterized using a portable NanoVNA-F V3. A tissue-mimicking phantom was prepared using distilled water, agar-agar, glycerin, sodium chloride, and sugar, with spherical tumor inclusions of 4, 7, 10, 13, and 16 mm diameter. The S21 transmission coefficient was evaluated for tumor-free and tumor-loaded phantom configurations in both simulation and experiment. The measured antenna resonances occurred at 3.61 and 4.15 GHz, with S11 values of −17.88 and −19.84 dB and VSWR values of 1.33 and 1.31, respectively. For the phantom experiments, S21 exhibited a consistent decrease with increasing tumor diameter at both investigated frequencies. At 3.08 GHz, the measured S21 changed from −57.03 dB for the tumor-free phantom to −66.09 dB for the 16 mm tumor, while at 4.28 GHz it changed from −47.05 to −55.04 dB. A simulated peak 10-g averaged SAR of 0.348 W/kg was obtained at 3.08 GHz. These results experimentally demonstrate the sensitivity of the proposed antenna-phantom configuration to controlled tumor-size variation and establish a low-cost platform for further development of microwave tumor-sensing systems. The present work is limited to homogeneous phantom validation and should therefore be regarded as a proof-of-concept study rather than clinical diagnostic validation.