Design And Analysis Of High-gain Ring Patch Antenna

Circularly polarized(CP)microstrip antennas are used in many systems,such as communication,radar,and medical microwave image sensing owning to its simple structure,low profile,small size and many other advantages.The wideband circularly polarized antennas and reconfigurable antennas have been studied in the past literature in order to obtain simpler structure of the system and improve the device portability.In this dissertation,a circularly polarized cut ring microstrip antenna,the wideband circularly polarized ring patch antennas and a polarization-reconfigurable microstrip antenna are studied and designed.Firstly,a single-fed high-gain circularly polarized ring microstrip antenna,which consists of a radiation patch and a ground plane,is designed.Compared with conventional microstrip antenna with substrate,the higher gain is achieved due to use the air layer between the radiated patch and the ground plane for the less amount of stored energy under the metalized patch.The circular polarization is obtained by two unequal-length arc-shaped radiation patches,which excite two orthogonal linearly polarized modes with a 90° phase difference.The antenna is fabricated and measured to verify the design.The measured results are in good agreements with the simulated one.The measured results show that the impendence bandwidth(IBW)for |S11| <-10 d B is 16.7%(3.78 – 4.47 GHz)and the axial-ratio bandwidth(ARBW)for AR < 3 d B is 3.6%(4.09 – 4.24 GHz).Further,the gain is higher than 10.0 d B from 4.09 to 4.24 GHz.The antenna radiation pattern performs well over the whole band,and the peak gain can reach 10.67 d B at 4.11 GHz.Secondly,the methods of broadening the circularly polarized ring microstrip antenna are studied.The operating bandwidth of the circularly polarized ring microstrip antenna is widen by using different shape of the radiation patches.In this part,three wideband circularly polarized ring microstrip antennas are simulated and measured.The radiation patches are the square-ring patch(antenna 1),the ring patch with round outter outline and square inner contour(antenna 2),the ring patch with square outter contour and round inner outline(antenna 3),respectively.For antenna 1,the measured axial ratio bandwidth(ARBW)for AR< 3 d B of around 5.4%(3.25-3.43 GHz)is achieved.The axial ratio bandwidth for AR < 3d B of antenna 2 and antenna 3 are approximately 6.2 %(3.74–3.98 GHz)and 6.1 %(3.80–4.04 GHz),respectively.As a results,the operating bandwidth of the antenna is enhanced effectively by using different shape of the radiation patches.A polarization-reconfigurable cut ring microstrip antenna with high gain is designed.The microstrip antenna consists of a ring radiation patch,PIN diodes,non-metallic columns and ground plane.By controlling the PIN diodes,the antenna can be operated on three polarized states: one state for linear polarization(LP),one state for left hand circular polarization(LHCP),and one state for right hand circular polarization(RHCP).In addition,the antenna peak gain can reach 10.0 d B for LP,LHCP and RHCP over the operating bandwidth and stable unidirectional radiation patterns.By analyzing simulated and measured results,the measured common operating bandwidth of the proposed antenna on three states is from 3.86 to 3.98 GHz with the relative bandwidth of 3.1%.The cross-polarization of the antenna on the whole states is very low.Good polarization-reconfigurable characteristics of the proposed antenna have been obtained from 3.86 to 3.98 GHz.