The Research And Design Of Multiband And Broadband Circularly Polarized Microstrip Antenna

With the rapid development of wireless technology,it is usually necessary to integrate multiple functions at the same device,so that it can communicate with multiple devices on different frequencies.For example,the GNSS（Global Navigation Satellite System）requires that it can provide service signals in L1（1.575 GHz）,L2（1.227 GHz）and L5（1.176 GHz）frequency bands,while C-band commercial communications satellites typically operate in the 4/6 GHz band（4 GHz for downlink data transmission and 6 GHz for uplink data transmission）.On the other hand,the equipment using the circularly polarized（CP）antenna can receive the electromagnetic signals transmitted by the satellite in different attitudes,which can eliminate the polarization mismatch and multipath effect encountered in the propagation of radio waves,thus improve the system performance and positioning accuracy.With the increasing shortage of spectrum resources,multi-band and multi-polarization antennas have become a research hotspot.In order to meet the needs of cross-band and polarization-reusing for the new generation of wireless systems,two novel multi-band CP antennas based on sequentially rotated feeding technology are proposed in this dissertation.The main research results of this article are as follows:1.A triple-band CP antenna with wide axial ratio bandwidths（ARBW）working in C/X band is designed.By loading theλ_g/4 short-circuit stub in the main line of the phase shifter,the control of the phase output slope of the main line and the broadening of the phase bandwidth of the phase shifter are realized.On this basis,a four-port sequentially rotated feeding network is designed.The four orthogonal signals with constant amplitude and phases of 0°,90°,180°and 270°completely cover the three design frequency bands,the linearly polarized（LP）radiation of the array element at 6,7 and8.5 GHz is successfully transformed into the CP radiation.In addition,the antenna has the same RHCP handedness at three bands,the 3 d B ARBW reaches 15.2%（5.4-6.2GHz）,11.4%（6.7-7.4 GHz）and 15.3%（7.7-9 GHz）,and the maximum gains corresponding to the three frequency centers are 8.3,9.8 and 6.3 d Bic,respectively.The antenna has the advantages of unidirectional radiation,wideband and high gain,which can provide a new method for the design of planar integrated and wideband satellite communication antenna.2.A wideband dual-band CP antenna working in C/X band is designed,which could radiate the left-hand circularly polarized（LHCP）waves at low frequency and right-hand circularly polarized（RHCP）waves at high frequency.The degenerate modes TM₁₀ and TM₀₁ excited by two orthogonal I-shaped feeding slots,achieve the high ports isolation and independent frequency tuning.In addition,the impedance bandwidth and gain bandwidth are significantly improved by introducing a parasitic structure.Another advantage of this design is that the frequency ratio（FR）of the two operating bands is 1≤f₂/f₁≤1.5,the FR can be equal to 1 for a square patch.The measured results show that this antenna possesses impedance bandwidths exceed 20%for both bands,and the3 d B ARBW is 10%at 6 GHz and 16.5%at 8.5 GHz.The opposite CP senses with measured gain of 9.3 d Bic and 10.1 d Bic at two bands can also be used for signals receiving and transmitting respectively.It is expected for the proposed antenna to play an active role in wireless applications such as duplex communication or polarization multiplexing.