Analysis of Antenna Performance of Flexible F Shaped Antenna with a Defected Ground Structure Using Different Substrates for Biomedical Applications

In this work, a F shaped microstrip patch antenna for biomedical applications, is designed on two different substrates of varying thicknesses, and the effects of dielectric constant and thickness of the substrate are studied and analyzed on antenna performance. The two substrates chosen for the purpose is FR-4 and Rogers/Duroid RT 5800, both of which are easily available for fabrication. FR4 has a dielectric constant 4.3 and the thicknesses chosen for this work is 0.8 mm and 0.25 mm, while ROGERS DT5880 has a dielectric constant of 2.2 and the thicknesses chosen are 0.8 mm and 0.13 mm. Since, the antenna is designed for biomedical purposes, the frequency band of operation is chosen as ISM band <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(2.4-2.5 \text{GHz})$</tex>. The designed antenna is simulated on CST Microwave Studio and its return loss, resonant frequency, bandwidth of operation and absolute gain are analyzed. The antenna designed on Rogers 5880 of 0.13 mm thickness gives the best performance and therefore bending test of the same is carried out in the software, for conformability analysis. It shows the highest gain of 1.36 dBi with the largest bandwidth of 0.9 GHz. The antenna is tested with a three-layer bio mimic human phantom and SAR is simulated. The antenna shows a permissible value of SAR as <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.04 ~\mathrm{W} / \text{kg}$</tex> for a 1 g of human tissue. These simulation results have been used as a reference to choose the type of substrate to design he antenna for biomedical applications of interest.