Millimeter-wave Broadband Low Profile Reflectarray

Compared with traditional phased array antennas,planar microstrip reflectarray are widely used in satellite communication,remote sensing and radar systems due to simple feeding structure,high gain and low cost.However,the planar microstrip reflectarray has the disadvantage of narrow bandwidth due to the inherent narrow-band characteristics of the microstrip patch unit and the differential spatial phase delay of the feed to the radiating unit on the reflectarray changing with frequency.The problem of narrow bandwidth limits the application scenarios of planar microstrip reflectarrays.The realization of high gain is based on the large-diameter antenna,and the profile of the antenna also increases,which is not conducive to the conformality of the antenna and the carrier platform.Designing a microstrip reflectarray that can satisfy both broadband and low profile is of great significance to the development and application of modern wireless communication systems.Using different design methods,this thesis proposes two broadband low-profile reflectarrays operating in the millimeter waveband.The details are as follows:1.In view of the narrow bandwidth of large-diameter planar microstrip reflectarray,this thesis abandons the design method of the center frequency phase compensation mechanism of traditional reflectarray,and proposes a method for tracking and compensating the phase changes of antenna arrays.Based on this method,three single-layer reflection elements with different frequency-phase(F-P)response capabilities and spatial dispersion tracking compensation capabilities were used to design and manufacture an approximate elliptical array with a major axis length of392 mm,a minor axis length of 336 mm,and a focal-to-diameter ratio F/D of 0.6.According to the test results: the reflectarray can obtain a 1-d B gain bandwidth of27.5%,the maximum gain is 37.78 d Bi,and the maximum aperture efficiency is 45.5%.The designed reflectarray solves the problem of high gain and working bandwidth of the antenna at the same time.2.A double-layer broadband dual-polarization unit with high isolation is proposed.The double-layer structure of the unit can independently control the reflection phase of two orthogonally polarized waves.Based on the principle of polarization rotation,and on the basis of broadband dual polarized units,a broadband polarization rotation unit is proposed,which achieves a large phase coverage of more than 600 ° and a high polarization rotation rate by virtue of the three-resonance structure.Using the polarization rotation unit,a folded reflectarray with an aperture surface of 143mm×143mm and a focal-diameter ratio F/D of 0.56 is designed.The folded reflectarray consists of a feed source,a polarization selection surface,and a polarization rotation surface.And adopt the method of multi-frequency phase matching to optimize the phase distribution of the main reflectarray.The test results show that the folded reflectarray can achieve a 3-d B gain bandwidth of 28.6%,with a maximum gain of 31.32 d Bi at34.9GHz,a maximum aperture efficiency of 41.2%.The designed folded reflectarray can achieve broadband while maintaining a low profile.