Researches On Dual-band And Broadband Circularly Polarized Antennas

As a key component of radio equipment, antenna has a critical influence on the performance of communication system. Because of high efficiency of receiving and effectively restraining the interference of rain and fog, the circularly polarized antenna is widely applied in the fields of radar, mobile communications, electronic interference and satellite positioning system and so on. The researches and explorations on dual-band and broadband technologies of circularly polarized (CP) antenna have done to the requirement of research projects. A dual-band CP microstrip patch antenna and two broadband CP spiral antenna are designed and optimized.Firstly, the recent research status of dual-band and broadband CP antenna is presented, then the basic theory of microstrip antenna and its main methods to achieve circular polarization are summarized. After that the planar spiral antenna is described, including the model, working principle and characteristic parameters. The final is about the design of three circularly polarized antenna. Details are as follows:A single-feed CP microstrip antenna is designed to covering L-band and S-band of beidou satellite navigation system (CNSS). Stacked patches with corner truncated are employed to get dual-band circular polarization. An air layer is applied to reduce the relative dielectric constant and a small capacitive metal piece is loaded to offset inductance, both methods are used to achieving a broad band. The results of numerical simulation show this antenna with good performance. In detail, the obtained impedance bandwidth in the L-band and S-band are about82MHz and156MHz, and CP bandwidths are about18MHz and38MHz. The antenna is not only with dual-band CP radiation, but also with bandwidth enhanced in each band. This increases the effectiveness and reliability in different environments. Finally, the antenna is manufactured and the measured result matched well with the simulated result.Two broadband CP planar spiral antenna with operating frequency in1-12GHZ are designed. According to project requirements and theoretical knowledge of planar spiral antenna, a planar equiangular spiral antenna is designed first. In order to achieve the conversion between equilibrium and non-equilibrium, as well as the transformation between the input impedance of antenna and the characteristic impedance of coaxial line, an easy processing ultra-wideband balun is designed, its structure is a trapezoidal double-sided microstrip line. At the same time, an absorbing resistor at the end of each spiral arms is loaded to improve axial ratio in low frequency. Finally, a broadband CP planar equiangular spiral antenna with dual radiations along axial direction is obtained successfully. According to one side radiation on antenna for the application environment, some changes are made later. An Archimedean spiral antenna with a shaped reflector cavity and a better exponentially gradient microstrip balun is designed. In view of ultra-wideband, segmented simulation are done by using electromagnetic simulation software. In the end, a detailed analysis and discussion are made, such as the input impedance, the axial ratio, the pattern and the gain. The results show that all the performance achieve the project targets.