Research On The Key Technologies Of The Broadband, Dualband, And Variable Polarization Reflectarray Antennas

With the improvement of the technologies in the 21 st century,reflectarray antennas have been a quite popular issue,thanks to their advance features e.g.low-cost,high efficiency,easy to conformal deployment,and the reconfigurability.It is very important for reflectarray antennas to improve and innovate the design methods,promote the characteristic parameters,and adapt to more applications.By using theoretical analysis and experimental verification,some researches at the frequency domain and the polarization domain,focusing on broadband,dual-band,and variable polarization reflectarray antennas is presented in this dissertation.The operational principle,common cell types,design process and analysis methods of reflectarray antennas are introduced in chapter one and two.According to the different applications and techniques,the key design points of several different types of reflectarray antennas are discussed in the subsequent chapters,respectively.Meanwhile,the respective design examples and experimental results are delivered to prove the design methods.Major outlines and contributions of the dissertation are as follows:(1)The research on the phase-optimized multi-resonance reflectarray cell is presented.As the energy is tightly bounded in the centre of the traditional double cross loop unit,which is a typical multi-resonance reflectarray cell,it would suffer from higher loss and steeper phase curve.To solve this problem,a modified cross unit is proposed,in which an inner cross solid patch replaces the inner cross loop.Lower loss,more linearly phase curve,and wider bandwidth could be obtained to increase the distance between the two resonance points.A single layer Ka-band reflectarray consists of the proposed unit has 18% 1.5-dB gain bandwidth,which increases by 50% compared with the traditional double cross loop.(2)The improve technique of the multi-resonance cell is investigated.In order to improve the performance of the linear curve and bandwidth of multi-resonance cells,sub-wavelength lattice and fractal geometries are introduced in the multi-resonance unit to achieve the miniaturized cell.A large linear phasing range of 420° can be achieved by using a Minkowski double square loops loaded by spiral stubs(MDSL-SS)unit in only(0.27λ0)2 areas.Meanwhile,a simple equivalent circuit approach is derived to analyze the intricate reflectarray element and guide the design.The reflected characteristics of reconstruct elements which use new substrates and cell structures with the specified metal-patterns,can be rapidly calculated by the proposed model over the operating bandwidth without the full-wave simulation.A single layer X-band reflectarray,which consists of the sub-wavelength multi-resonance MDSL-SS,is fabricated and measured.The measured 1-dB gain bandwidth is 38%,while the counterpart of the traditional double square loop is only 9%.Its performance improves significantly.(3)A design method based on mutual coupling control of dual-band dual polarization reflectarray antennas for high working frequency and frequency ratio applications is studied in this dissertation.Ka/W dual-band dual-polarization reflectarray antenna would suffer from high electrical interference,high frequency ratio,and the risk of the processing and assemblage.There are two challenges in the unit design: one is that the narrow bandwidth and steep reflected phase curve of single layer dual-band unit,and another are that the extraordinary loss and processing risk of the support structure of the dual-layer unit.To solve these two problems,three different types of stacked elements: cross-dipole element for the Ka-band,modified phoenix square loop,and square patch for the W-band operation are presented.The simple geometries of the unit are easy to fabricate.Moreover,enough reflected phase range can be achieved by using the vertical coupling without increasing unit areas.Cell substitutions,phase staircase approximations at W band,and a new unit choice strategy based on the local characteristic of the proposed units are presented to eliminate the variation range of the coupling effect and improve the local periodic condition.The measured results of the proposed reflectarray show that the prototype has good radiation performance at the both bands and satisfys the design specifications.(4)A solution based on the controllable wave-path difference to the variable polarization reflectarray antenna is investigated.There are some problems on traditional passive variable polarization reflectarray design,e.g.eliminating the orthogonal phase coupling,improving the cross polarization isolation,and implementing arbitrary phase difference Δδ of the two polarizations.To solve these problems,a passive variable polarization reflectarray can transform a linear polarization(LP)mode into an arbitrary polarization mode by using controllable the polarization tilt angle γ and phase difference Δδ.According to this solution,dual-layer three parallel dipole loops loaded by a phase-delay air cavity are presented.The proposed units on two layers,are used to compensate for the space phase delays θx,y of two orthogonal polarizations with low mutual coupling.A metal grid ground between the proposed units,is applied to decompose the orthogonal LP components and depresses the cross coupling.The phase-delay air cavity could provide the controllable wave-path difference to independently control the phase difference Δδ of two orthogonal LP components.Four different polarization states of right-hand circularly polarized(RHCP),45 ° LP,left-hand CP(LHCP),and 135°LP,which are controlled by simply rotating the feeder and adjusting the distance between the dual-layer cells,are measured and validated with a specific incident LP wave.