Design Of A Fractal Wearable Antenna For Marine Rescue

The key point in maritime search and rescue is to find the overboard people quickly and accurately. An antenna is an important component of the maritime search and rescue system. Traditional maritime search and rescue systems include the Search and Rescue Transponder (SART) System and the Emergency Position Indicating Radio Beacon (EPIRB) System, both are too large to be equipped. Therefore, it is needful to design a light-weight compact wearable antenna having low-profile, flexibility and durability so that it can be easily equipped with the overboard people for the maritime search and rescue system.In this thesis, the environmental influences on the performance of antennas are analyzed. These environmental factors include the atmospheric waveguide, the sea mist and the sea water. Electromagnetic wave can be propagated over the horizon in the atmospheric waveguide, it is obvious that the vertically polarized antennas are more suitable for over-the-horizon propagation. The sea mist environment may cause the impedance performance of antennas to deteriorate. However, the relative permittivity and the wave impedance of the sea mist calculated in this dissertation reveal that the common sea mist has little effect on the performance of antennas. Once an antenna is placed above or partially immersed in the sea, the capacitance between the antenna and sea water will influence the antenna's performance.Secondly, based on the above analysis of antenna's performance under versatile environment conditions, a V-shaped two-order fractal monopole antenna operating at 142 MHz is designed. According to the environmental conditions, suitable angle ? for V-Shaped antenna and appropriate dimensions for ground plane are chosen. A prototype of the V-shaped antenna is fabricated using copper foil as conducting material. Measured results disclose that the antenna exhibits excellent return loss performance over the desired frequency band with almost omnidirectional radiation characteristics. The analysis of antenna bending and inclination effect further reveals that the effect of such factors in negligible on the performance of antenna.Finally, the proposed V-shaped antenna is miniaturized by introducing cuts in original structure. The electrical length of the V-shaped antenna can be increased by introducing these cuts, which reflects that the antenna dimension can be significantly reduced. Meanwhile, by adjusting the antenna structure and the position of feeding point, good matching performance can be achieved. Compared with that of the original V-shaped antenna, the dimensions of the miniaturized antenna are significantly decreased from 583mm x 386.4mm (0.276?×0.183?) to 320mm x 224mm (0.151?×0.106?) saving almost 70% of the area, which is very needful when it comes to body-worn antennas applications. It is justified that the miniaturized antenna still has good performance under the intended working environment for the antenna operation. The measured results show that the antenna has better return loss and good omnidirectional radiation above the water, justifying the compatibility and suitability of proposed antenna for maritime search and rescue applications.