Study of a water-immersed ultra-wide band microstrip patch antenna

In order to significantly improve the resolution of biological imaging, a water-immersed (the antenna is placed in the pure water) ultra-wide band (UWB) microstrip antenna is proposed in this paper. The aim of this paper is to determine the suitable wavelength of the interrogating radiation in the medium and to reduce the big reflection of the incident energy at the interface between the target and the medium surrounding the target. In this way, the frequency of 2.45 GHz is selected due to the compromise between spatial resolution and loss of signal, and the medium is chosen as water because of its relative permittivity close to the biological tissues. The design of the linear gradient impedance-matched patch antenna is proposed to match the antenna and the coaxial transmission line of 50 ohms. The simulation results are presented that the fixed percentage bandwidth of this antenna is about 0.923 (1.75 ~ 4.8 GHz) and the 3 dB gain degree range is from -30° to 30° except the null at the center from -6° to 6°, which are both good enough to satisfy the requirements for biological imaging system.