Study Of Broadband Microstrip Reflectarray Antennas

Reflectarray antennas have attracted wide attention in recent years due to its alluring advantages compared with the traditional high-gain antenna.This kind of antenna is generally composed of an array of radiating elements printed on a flat surface and illuminated by a feed antenna,which has already exhibited the advantages of low profile,low cost and high gain.Besides,it has been found flexible applications,such as achieving very accurate contour beam shape and multi-beam.This dissertation mainly focuses on the difficulties encountered in element and reflectarray design.We propose an approach to analyze mutual couplings between adjacent elements in a reflectarray antenna,and works on how to decrease them.Based on this analysis,broadband reflectarray antennas and dual-band reflectarray antennas have been thoroughly studied,and reflectarray antennas with improved bandwidth and dual-band single-layer linear-polarization reflectarray antennas have been realized,respectively.The major works and innovations are summarized as follows.1.The basic theory study of reflectarray antennas,including the basic characteristics,the advantages,disadvantages,calculation method of phase compensation,aperture efficiency and element simulation method.The infinite periodic element model has been utilized to analyze the radiating element.Based on the model,the effect of the element radiation performance due to oblique incident wave is analyzed followed by analysis on the radiation property of three typical radiation elements.2.The mutual coupling effects of adjacent elements are investigated: not only the difficulties in how to analyze but also the comparison of two common used methods have been compared with each other.To overcome the shortcomings of these two methods,a novel surrounding-element method based on surface electrical field distribution characteristics of the radiating element is proposed.More precise mutual coupling analysis can be achieved by this method,because all surrounding elements are illuminated by the incident wave.A 9-surrounding-element model has been established based on our proposed method and the mutual coupling effects of different kinds of elements with different adjacent elements have been investigated,which lays the foundation for the design of reflectarray antennas.3.The broadband reflectarray antennas are investigated.Among the all existing methods,the phase-delay-line technique has the ability to achieve linear phase responses in a wide range for single-layer elements.Besides,this technique is good for decreasing the mutual coupling of adjacent elements.Our research focuses on the phase-delay-line technique to broaden the bandwidth of reflectarray antennas with two novel broadband elements proposed.First,the novel structure of double-gapped rings with phase-delay lines has been proposed.A linear and smooth phase response can be obtained and parallel phase responses of different frequencies have been obtained as well,which is helpful for achieving wideband property.The reflectarray antenna based on this novel element has been designed and fabricated,and 20% 1-dB gain bandwidth is achieved.Second,the novel structure of triple-gapped rings with phase-delay lines has been proposed based on the first structure.This novel element has smoother phase responses than the first one.The slope of the phase responses is more stable and the parallelism of phase responses maintains well in a wide range of frequencies.Finally,the measured results of the designed reflectarray antenna based on this element show that 1-dB gain bandwidth has been remarkably improved up to 31.5%.4.The dual-band reflectarray antennas are investigated.An approach has been proposed to design a single-layer dual-band linearly polarized reflectarray with independent radiation patterns for each band.The couplings inside the element structure are utilized and the achievable response phases at two frequencies with wide range can be obtained by parameter sweeping.Based on this approach,a typical dual-band element,ring-dipole element,has been utilized to design and realize a dual-band linear polarized reflectarray antenna with different beams for each band so as to demonstrate the effectiveness of the proposed approach.Because of the inadequate phase range of ring-dipole element,a novel single-layer dual-band dual-linear-polarization element,i.e.ring-crossbowtie element,has been proposed.The designed reflectarray antenna based on the ring-crossbowtie element has been fabricated and measured,and the measured radiation patterns show better performances at both frequencies.