Research On A New Broadband Planar Reflectarray Antenn

For most radar and long-distance communications,high-gain antennas are indispensable.Parabolic antennas and microstrip array antennas are two types of traditional high-gain antennas.However,the parabolic antennas are bulky with poor maneuverability whereas the complex feeding networks of the microstrip array antennas cause losses and therefore affecting the antenna gain and efficiency.The reflectarray antenna combines the advantages of both the parabolic antenna and microstrip array antenna.In recent years,reflectarray antennas have received considerable attention from academia and industry due to their promising features such as high gain,high efficiency,light weight,and low cost.However,the main disadvantage of the traditional reflectarray antenna is the narrowband characteristic.For a medium or small size reflectarray antenna,its bandwidth is mainly limited by the narrowband characteristic of the unit-cell.This thesis first briefly overviews the current research progress of reflectarray antennas,explaining their principles and design methods.Then,in order to tackle the drawback of the narrowband behavior of traditional reflectarray antennas,several novel unit-cell structures are proposed for broadband reflectarrays.The main contents of this thesis are arranged as follows:1.A broadband reflectarray antenna based on a single-layer hook structure unit-cell is designed.A single-layer hook-shaped unit-cell structure is proposed.By changing the length of the hook-shaped unit-cell,a linear phase ranging 315° is obtained.A reflectarray antenna composed of 529 hook-shaped elements is simulated and designed.In order to reduce the feed blockage effect,the feed horn is offset by 25°.The simulation results show that the 1-dB gain bandwidth of the reflectarray antenna is 30.8%,and the gain at the center frequency of 10 GHz is 25.3 dBi,corresponding to aperture efficiency of 62.8%.2.A broadband reflectarray antenna based on a single-layer quasi-selfcomplementary structure unit-cell is designed.A single-layer quasi-self-complementary structure unit-cell is proposed for wideband reflectarrays.The unit-cell is composed of an inverted L-shaped metal strip and a rectangular metal patch etched with an inverted L-shaped slot,forming a quasi-self-complementary structure.By adjusting the length of the inverted Lshaped quasi-self-complementary structure,a linear phase variation exceeding 370° can be achieved.Based on the unit-cell,a reflectarray antenna hosting 529 elements and 25° offset fed is designed.According to the measurement results of the antenna,the 1-dB gain bandwidth of the designed reflectarray antenna is 38%,and an aperture efficiency of 59% is achieved at the center frequency of 10 GHz.3.A broadband reflectarray antenna based on a single-layer half-cut slotted circular ring unit-cell is designed.A half-cut slotted circular ring unit-cell is proposed for broadband reflectarrays.For the original structure of the slotted circular ring element,cutting along its symmetry axis in half,the overall size of the unit-cell is also halved.The performance of the unit-cell is similar to that of the original unit-cell.After parametric optimization,a more linear reflected phase curve is realized.A reflectarray antenna composed of 1058 half-cut slotted circular ring elements is fabricated and measured.The measurement results show that the 1-dB gain bandwidth of the half-cut slotted circular ring reflectarray antenna is 31%,and the aperture efficiency at the center frequency of 10 GHz is 65.4%.4.A dual-band broadband single-layer reflectarray antenna is designed.A singlelayer dual-band unit-cell is proposed.The unit-cell comprises a slotted rectangular patch and a hook-shaped structure which are orthogonally placed.The slotted rectangular patch is designed for the lower band centered at 10 GHz in one polarization while the hook-shaped structure is designed for the higher band centered at 18 GHz in orthogonal polarization.The simulation results show that the designed dual-band reflectarray antenna has a 1.5-dB gain bandwidth of33% with an aperture efficiency of 50.1% at the lower-band center frequency of 10 GHz,and a1.5-dB gain bandwidth of 20.7% with an aperture efficiency of 49.9% at the higher band center frequency of 18 GHz,respectively.The designed dual-band reflectarray antenna features a broadband performance in both frequency bands.