Research On Broadband Reflect Array Antenna And Its Folded Structure And Beam Scanning Technology

Reflectarray antennas are widely used in satellite communication and radar system owing to their appealing features like low-cost,low-mass,ease of fabrication,and beam scanning capability.This thesis mainly focuses on the research of reflectarray antennas,including two novel types of broadband reflectarray antennas,the low-profile design of a folded reflectarray antenna and its simple and low-cost beam scanning approach.The researches of this thesis are as follows:1.A wideband reflectarray antenna consisting of single-layer dipole elements attached with T-shaped stubs is proposed.A pyramidal horn antenna with a center frequency of 10 GHz is firstly designed as the feed for the reflectarray antenna.The single-layer dipole element attached with T-shaped stubs is then presented.By varying the lengths of the T-shaped stubs,the unit cell can provide a linear phase curve covering about420°.Using this novel type of unit cells,a 441 element 25° offset-fed reflectarray at 10 GHz is designed and developed.The experimental results show that the proposed reflectarray can achieve 1-d B gain bandwidth of 24% and 1.5-d B gain bandwidth of 37%.In addition,aperture efficiency of 66.6% is obtained at 10 GHz.2.A broadband single-layer reflectarray antenna comprising circular ring elements dented with sectorial slits is presented.A novel single-layer circular ring element dented with sectorial slits is proposed,the sizes of circular rings are fixed and equal for all elements,while the variation of the reflected phase is obtained by varying the lengths of the sectorial slits dented within the circular rings.In this arrangement,the rapid geometric variations among the neighboring elements encountered in conventional reflectarray antennas can be prevented.The proposed element can yield a linear reflected phase and the range of phase variation is close to 360°.Using the proposed unit cells,a 25° offset-fed reflectarray containing 529 elements is designed and built.Experimental results indicate that the designed reflectarray antenna can realize a broad 30% 1-d B gain bandwidth with a 58.3% aperture efficiency.3.A folded reflectarray antenna using single-layer three-dipole elements is proposed.The antenna consists of a feed horn,a lower reflectarray,and an upper polarizer.A three-dipole element is employed as the unit cell to realize a broadband performance of the folded reflectarray.The design is carried out at 10 GHz and constituted of 1089 elements on a408 mm×408 mm aperture.The proposed folded reflectarray antenna has a low-profile configuration compared with traditional reflectarray antennas.The simulated results show that1-d B and 1.5-d B gain bandwidths of 14% and 22% with an aperture efficiency of 47% at 10 GHz are achieved.4.A simple and low-cost beam steering method for low-profile folded reflectarray antennas is presented.The beam scanning is realized by rotating metasurfaces placed in a close proximity to the antenna.Contrary to electronically beam steering approaches where active devices are required,this method employs completely passive metasurfaces to steer the beam and consequently resulting in a simple,low-cost and low-profile configuration.Two rotatable metasurfaces are designed and placed above the folded reflectarray antenna.Simulation results show that this method can achieve beam scanning covering azimuth angles of 0°-360° and elevation angles of 0°-42° with the gain variation less than 3 d B.