Study On Broadband Planar Reflectarrays And Multilayer Frequency Selective Surfaces And Their Applications

Reflectarray antennas and frequency selective surfaces are developed and investigated by many researchers to realize good characteristics and improve performance of electromagnetic radiation and scatter of antennas in a variety of applications including wireless communication, satellite communication and future deep space exploration. Broadband planar reflectarrays and frequency selective surfaces are being attracted more attention of researchers in electromagnetic fields. First, a broadband planar reflectarray is designed based on dual-resonant conformal loop array. Then, a broadband frequency selective surface is designed using a multilayer periodic structure based on sub-wavelength elements, which is analyzed and synthesized in detail. At the same time, a novel mechanically operated reconfigurable polarization converter based on the multilayer frequency selective surface is proposed to achieve polarization diversity including broadband linear, left-and right hand circular polarizations in this dissertation. Additionally, three reflective multi-band and multi-polarization converters are designed based on anisotropic metasurface which can convert linear polarization to cross-linear polarization, right-and left-hand circular polarizations. These are major researched in this dissertation.Specially, the main contributions of this dissertation are summarized as follows:The first one is that the three calculation methods of spatial phase delay about array antenna including reflecting and transmitting types are presented based on the basic array antenna theory and geometrical theory. The introduction and description provide a firmly theatrical basis to design the broadband planar reflectarraySecond, a broadband reflectarray antenna is proposed and designed based on dual-resonant conformal loop element. By utilizing variable parameters of the DRCL element, a nearly progressive phase-shift ranging more than 550° is achieved for reflecting wave within a wide band. It is important that a small DRCL element can be flexibly used to generate a 360° phase shift, which decreases the cell period between the neighboring elements. That is to say, the proposed reflectarray element is miniaturized. The DRCL element is less sensitive to the variation of incidence angles for both TE and TM polarizations. More importantly, the broadband reflectarray, whose 1 dB gain-bandwidth is up to 20%, can be applied in practical wireless communication system in order to cover the desired region. At the same time, the reflectarray antenna can be used in synthetic aperture radar (SAR) imaging.The third one is that a synthesis method is proposed to synthesize multilayer frequency selective surface (MFSS). The equivalent circuit model (ECM) corresponding to the MFSS is used to synthesize the electrical and structural parameters of the MFSS using the synthesis theory of a bandpass filter. Compared with the traditional design method, the ECM synthesis method of the MFSS greatly reduces the design period. The general ECM corresponding to MFSS based on Minkowski sub-wavelength is given and simplified, and then the general prototype of coupled filter is obtained. The Minkowski fractal patch is non-resonant and provides an inductor, and the Minkowski fractal slot on the ground is non-resonant and provides a capacitance. The thin substrate is equivalent to a J/K inverter and the passband LC resonant mode is produced. Then, the bandwidth of frequency selective surface can be broadened by cascading multilayer first-order FSS. The structural parameters are determined according to the electrical parameters. The simulated and measured results verify the effectiveness and correctness, which provides the guidance for MFSS design.Another contribution is a mechanically polarization-reconfigurable converter that is firstly proposed using multilayer frequency selective surface (MFSS). A MFSS is designed based on the synthesis technology using subwavelength patch arrays and grid lines separated with thin substrates. The operating bandwidth can be widened by cascading multi-layer periodic structure. The perturbation is introduced into the synthesized multilayer FSS to produce two different magnitude and phase responses in two orthogonal directions. It can be known that electromagnetic wave propagates with the desired polarization state when certain conditions including the magnitude response and phase difference response in two orthogonal directions are satisfied. Furthermore, theatrical calculation method of axial ratio (AR) is presented for the ideal and simulated cases (infinite array). Simulated AR of finite array is compared with measured and theatrically calculated ones. The results of them are discussed and the differences among three cases are analyzed in detail. In addition, some factors of discrepancy are given. The results show that polarization state can be transformed between linear and circular polarizations. This polarization converter can be used to resolve Faraday rotation when electromagnetic wave propagates in the ionosphere in satellite communication.Finally, three reflective multi-band and multi-polarization converters are designed based on anisotropic metasurface. The transformation can be realized between different polarizations due to different magnitude and phase responses in two orthogonal directions. That is to say, linear polarization can be converted to cross-linear polarization, right-and left-hand circular polarizations. The transformation between different polarizations means the anisotropic metasurface can modulate the polarization states of electromagnetic waves. The first polarization converter is a highly selective polarization converter, which consists of a thin dielectric layer, a truncated square patch layer and a ground layer. The operating frequency and sharp skirt property are related with the sizes of the truncated corner and truncated square patch, respectively. The second is a multi-band and multi-polarization converter which is designed and studied on the basis of the first one. The characteristics of multi-band and multi-polarization transformation are obtained by stacking the truncated patch layer. The third one is a broadband polarization converter designed using stacked three patch layers with truncated corners. The stacked element can obtain multi-resonance property and broaden the operating band. Simulated results of finite array agree well with these of element. The simulated results of element and finite array show three multi-band and multi-polarization converters based on anisotropic metasurface can realize the transformation between different polarizations. In other words, linear polarization can be reconfigured to linear polarization, right- and left-hand circular polarizations.