Reseach On Broadband And Dual-Band Miniaturized Circularly Polarized Microstrip Antennas

Since the concept of the microstrip antenna of was put forward, the microstrip antenna has been used in satellite communications and so on, because it has the advantages of the low-profile, the low weight, the conformability and so on. Especially the circular polarization microstrip antenna has some significant advantages, which has making that the circular polarization antenna has strong anti-interference ability, it has been widely used in many aspects, such as communication, radar and electronic reconnaissance, countermeasure.Focused on the circular polarization microstrip antenna, this paper firstly introduces the research status of circular polarization microstrip antenna in recent years, and then briefly introduces the basic theory of microstrip antenna and circular polarization technology. Then some typical circular polarization microstrip antenna and the latest progress are introduced. The final is about the design of three circular polarization microstrip antenna in this paper, Details are as follows:A dual-layer dual-band compact CP microstrip antenna is designed. Stacked patches are employed to get dual band. By notching two symmetrical circular holes and annular gap in the patch, not only the circular polarization is realized, and the dimensions of the antenna are reduced. By adding an air layer between two substrates and loading a small capacitive metal piece, the bandwidth is further improved. The results show that the antenna can effectively cover L-band and S-band of the beidou satellite navigation system (CNSS), and the antenna size is reduced by about 15%.Then a microstrip slot antenna fed by a modified L-shaped microstrip feed is designed. Firstly, we can estimate the width of the microstrip feed according to the formula. The proposed broadband circular polarization(CP) operation is achieved by protruding a pair of 90°annular-ring structure. By using a modified L-shaped microstrip feed, the antenna impedance matching becomes better, the impedance bandwidth and CP bandwidth are further improved. Finally, the proposed antenna can provide an impedance bandwidth of 66.9%(2.12～4.25 GHz) and a 3-dB AR bandwidth of 61%(2.12～3.98 GHz), and the measured AR bandwidth is about 43.8%(2.5～3.9 GHz).The last one is a broadband CP patch antenna for UHF RFID reader. The trapezoidal truncations are employed on the radiation patch to excite the circular polarization. By notching a square annular aperture around the coaxial probe, the capacitive feeding method is used, the bandwidth is effectively improved. And an thick air layer is applied to reduce the relative dielectric constant. The results show a 10-dB impedance bandwidth of 37% and a 3-dB axial ratio bandwidth of 5.5%. And that this proposed antenna achieves a gain level of more than 7.8 dB.