Design Of Circularly Polarized Antenna Array Based On Partial Coupling

With the development of navigation technology, broadband and miniaturized antenna technology is continuous research hotspot. It is very important to study the circularly polarized antenna, especially the wideband and low-profile antennas. Based on the research subjects and practical requirements of navigation system, this dissertation is mainly concerned with wideband circularly polarized antenna, compact circularly polarized antenna with high dielectric constant material and a partially coupled circularly polarized antenna array. The author's main contribution is outlined as follows: 1. A circularly polarized patch antenna is designed. The antenna adopts a double layer structure and the size of which is 60mm?60mm?5mm by using FR4 substrate. A microstrip is introduced into the feed probe to offset the inductive effect of the long feed probe, and therefore the impedance characteristics of the antenna are improved. The 3dB axial ratio bandwidth and impedance bandwidth are overlapped. It can be seen from the results that the circular polarization can be achieved with a 3dB axial ratio bandwidth of 20 MHz and a maximum gain of 4.2dBi. Moreover, the antenna exhibits good hemispheric coverage characteristic. 2. In order to realize the miniaturization of antennas, ceramic substrate with relative permittivity of 37.5 is employed to design two circularly polarized microstrip antennas. The size of conventional ceramic patch antenna is reduced by 60% compared with the aforementioned antenna using FR4 substrate. The results show that the antenna working at the center frequency of 1.268 GHz has a 3-dB axial ratio bandwidth is 3MHz, axial ratio at the center frequency is 2.2dB. In order to improve the 3-dB axial ratio bandwidth and gain of the antenna, the other ceramic antenna is designed by employing 4 rotating parasitic elements around the radiation patch of the conventional ceramic patch antenna. It can be seen from the results that the circular polarization can be achieved with a 3-dB axial ratio bandwidth of 6MHz, axial ratio of 1.7dB at center frequency point. 3. A 2?2 antenna array is designed based on partial coupling effect of the unit. The size of ceramic antenna element is 0 0 00.076l ?0.076l ?0.021l. The oversize of this array is 0 0 00.245l ?0.245l ?0.021l, and the element spacing of which is 00.17l. The radiation of the left-handed circularly polarized wave is suppressed by the coupling effect of elements, and the circular polarization of the antenna array is improved obviously. The results show that the antenna working at the center frequency of 1.268 GHz has a 10 dB return loss bandwidth of 40 MHz, 3-dB axial ratio bandwidth of 10 MHz, axial ratio of 0.4dB at center frequency point.