Research On Circularly Polarized Array Antenna With Shaped Beam

With the development of the 5th-Generation communication application and the growth of people's demand,the functions of antenna in modern communication systems keep increasing.Compared with a single antenna,the array antenna can achieve more functions,which can meet more needs of people.By means of beamforming technology,the excitation distribution of each element of the array antenna can be reasonably controlled to form the required radiation pattern.These array antennas with shaped beams can meet the requirements of different application scenarios.The following contents are mainly studied in this paper:Firstly,shaped beams with a low side lobe level are realized for conventional array antennas.The circularly polarized microstrip antenna is used as the array element,and uniformly arranged to form a 1×16 linear array and a 7×7 planar array,respectively.For the 1×16 linear array,a method of beam shaping based the Taylor distribution is used to realize the flat-topped beams and the cosecant square beams with a side-lobe level of-25dB and-35 dB respectively.For the 7×7 planar array,by using the same method again,the flat-topped beams and the cosecant square beams with a side-lobe level of-20 dB and-30dB are realized respectively.All the shaped beams have perfect circular polarization characteristics.Secondly,the effects of sequential rotation arrangement on the bandwidth and circular polarization characteristics of the array antenna are studied.To begin with,a compact wideband circularly polarized array antenna is realized by rotating four microstrip antennas sequentially.The antenna adopts a simplified serial feed network,which greatly improves the impedance bandwidth.Furthermore,by adding the parasitic elements with sequential rotation,the axial ratio bandwidth is effectively increased.The fabricated antenna size is only 0.93?₀×0.93?₀×0.017?₀,where?₀ represents the free space wavelength corresponding to the center frequency 10.4 GHz.Meanwhile,the measured 10-dB impedance bandwidth is 13.6%?from 9.8 GHz to 11.23 GHz?,and the measured 3-dB axial ratio bandwidth is 11.2%?from 9.9 GHz to 11.07 GHz?,and the maximum gain is 9.8dBi.Then,the effect of sequential rotation on the circular polarization characteristics is studied.The performance of two 4×4 microstrip arrays with the same array elements are compared,but one adopts the conventional uniform arrangement and the other uses the sequential rotation arrangement.The results show that when the main beam is scanned to the same angle,the sequential rotation arrangement is more advantageous to achieve good circular polarization characteristics of the array antenna.Thirdly,the shaped beams are realized for complex circularly polarized array antennas,including sequential rotation planar array and cylindrical conformal array.The iso-flux pattern and the omnidirectional conical beam are realized for the 4×4sequential-rotation planar array,respectively.Then the array elements are adjusted and rearranged to build an 8×8 sequential-rotation planar array,and an iso-flux beam is realized in its impedance bandwidth,which verifies a good broadband characteristic.Next,the microstrip antennas are rotated sequentially and are conformal to the surface of a cylinder.Then they are optimized to achieve stable wideband flat-top beams and cosecant square beams with a good circular polarization characteristic.Meantime,flat-top shaped beams and cosecant square shaped beams are realized for sequential rotation planar arrays and cylindrical conformal arrays of the same size.The excitation distributions are compared,and the excitation changes caused by cylindrical conformal arrays and their effects on shaped beams are analyzed.