Design and performance analysis of flexible microstrip patch antenna with rubber substrate at 2.45 GHZ

Abstract

In this work, a flexible antenna using rubber substrate is proposed to operate at 2.45 GHz within the ISM band for Medical and Wi-Fi/WLAN application. Several rubber materials with different carbon filler composition have been selected as the substrate in designing the antenna which include (1) natural rubber, (2) rubber with 20% carbon filler, (3) rubber with 25% carbon filler and (4) rubber with 50% carbon filler. The performances of these antennas are simulated and analyzed based on the return loss, bandwidth and gain. In addition to that, the performance of the antenna is not just simulated on a flat condition. A bending condition with different bending radius and direction are simulated as well. Based on the simulation results of the initial design, antenna with 25% carbon filler exhibit the best overall performance. The conclusive factor is the fact that the antenna exhibits a wide bandwidth (81 MHz) with acceptable gain (1.91 dB) compared to the other antennas. The return loss for this antenna is -35 dB which is considered good. Despite the good results obtained on a flat condition, the performance of the antenna at 2.45 GHz degraded when the antenna is bended which leads to the antenna modification by increasing the thickness of the substrate to improve the performance. With the first modified design, antenna with 25% carbon filler also exhibit the best performance overall among the others with a wide bandwidth (876.46 MHz) and considerably high gain (5.31 dB). The return loss for this antenna is -25.85 dB. On bending condition, it is observed that the return loss value at the intended frequency which is 2.45 GHz remain below -10 dB with acceptable bandwidth and gain, despite the direction and cylindrical radius of the bending. This proved that the antenna is usable at 2.45 GHz even under the bending condition. Second modification has been done by replacing the rectangular patch with circular patch to further prove that the method used by increasing the height of the substrate will also produce a wider bandwidth regardless of the design. With the second modified design, antenna with natural rubber also exhibit the best performance overall among the others with a wide bandwidth (1147.1 MHz) and high gain (7.36 dB). On bending condition, it is also observed that the return loss value at the intended remain below -10 dB with acceptable gain and bandwidth. Comparing the best modified rectangular patch antenna (rubber composited with 25% carbon filler) with the best modified circular patch antenna (natural rubber), it can be concluded that the modified circular patch antenna using natural rubber exhibits the best antenna performances. The design modification of the antenna to cope with the bending effect by increasing the height of the substrate can be considered as a success.