| With the rapid development of communication technology,the application of the phased array antenna in the communication field,especially on mobile platforms,is receiving more and more attention.The dual circularly polarized antenna,which has strong advantages of eliminating multipath interference,is capable of improving the isolation between the transmit and receive channels of the full-duplex communication system.Dual circularly polarized antennas are widely used in conformal phased arrays as they have numerous advantages,such as low profile,low cost,and easy conformity with the carrier.Also,they are the key components of a variety of different wireless communication systems.Therefore,the dual circularly polarized microstrip antenna is researched in this thesis.The main work and innovative achievements of this thesis include:(1)Based on the requirements of the X-band conformal phased array,a low-profile dual circularly polarized microstrip antenna is designed.A compact,wideband coupler is applied to achieve dual circularly polarized radiation,and the profile of antenna is only 0.09?.The antenna uses a through hole to connect the coupler and the patch,result in low processing difficulty and good structural stability.The measured results show that within the target frequency band,the voltage standing wave ratio(VSWR)and the axial ratio(AR)are separately less than 1.32 and2.59 d B,validating the design.A 24-element array,which utilizes sequential rotation feeding technique to improve the circular polarization performance,is also simulated.The AR in this band is lower than 0.34 d B.(2)A dual circularly polarized microstrip antenna with high isolation is designed.Higher requirements for the isolation of dual-port antennas have been put forward in many X-band communication systems.Based on the theory of scattering parameter networks,the analysis on the influencing factors of isolation is completed.The antenna,which uses a through hole and a rectangular strip to form an L-shaped probe,is fed by capacitive coupling.By introducing the foam medium with low dielectric constant and increasing the profile,the isolation is successfully optimized.In the target frequency band,the isolation is higher than 17.76 d B.(3)Two types of dual circularly polarized microstrip antennas suitable for some partial agreement bands of wireless local area network(WLAN)and global microwave interconnected access(Wi MAX)are proposed.The first S-band slot antenna of compact structure uses diagonal grounded strips to achieve circularly polarized radiation.In addition,the new resonance is introduced by embedding a pair of rectangular strips,and the antenna achieves a relative bandwidth of 33.7%.Based on the S-band slot antenna,a new type of wideband dual circularly polarized slot antenna is proposed by adding impedance matching strips and improving the feeding structure.Moreover,the antenna innovatively uses open slots and embedded rectangular strips to achieve a relative bandwidth of 87.9%.(4)A dual circularly polarized conformal phased array is researched.Two hemispherical conformal arrays are designed by using the top-added method and top-truncated method,the subspace division method.The first hemispherical conformal array contains eleven different kinds of subarrays while the second array only contains a semi-hexagonal subarray.Considering the requirements of the project and the cost,the second array is chosen.The 96-element array,which is at the top of the hemispherical conformal array,adopts sequential rotation feeding technique.At the maximum scanning angle,the gain of the array is higher than23 d Bi,the axial ratio is less than 1.33 d B,and the gain decreases less than 1.03 d B.The measured results show that the active VSWR of the two central elements are less than 2.19 and 1.94 at the maximum scanning angle,respectively. |
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