Phase Gradient Metasurface Radome Offering Beam Angle Translation and Wideband Absorption

A novel metasurface radome design is presented which combines the properties of a rasorber as well as a phase gradient metasurface (PGMS). By replacing the traditional frequency selective surface or lossless layer, in a radar absorber (i.e. a rasorber) with a PGMS, a new structure can be realised which provides dual-functionality in terms of both beam pattern control and wideband absorption. In particular, a 60 ∘ phase gradient metasurface is designed which is composed of six different unit cells (with the same periodicity) while being placed a quarter-wavelength below two lossy (or resistive) layers. By this stack-up configuration, the radome structure supports complimentary beam steering translation whilst providing absorption bands from about 1.3 GHz to 5.5 GHz and 6.1 GHz to beyond 10 GHz. This design, to the best knowledge of the authors, is the first example of a phase gradient metasurface rasorber (PGMSR) and has many interesting applications for future multi-functional radomes. It can also help to reduce the requirements for mechanical steering, antenna beamformers as well as array phase shifting networks

Miniaturized-Element Frequency-Selective Rasorber Design Using Characteristic Modes Analysis

A dual-polarization frequency-selective rasorber with two absorptive bands at both sides of a passband is presented. Based on the characteristic mode analysis, a circuit analog absorber is designed using a lossy FSS that consists of miniaturized meander lines and lumped resistors. The positions and values of resistors are determined according to the analysis of modal significances and modal current. After that, the presented rasorber is designed by cascading of the lossy FSS and a lossless bandpass FSS. Equivalent circuits of the frequency-selective rasorber are modelled, and surface current distributions of both FSSs are illustrated to explain the operation mechanism. Measurement results show that, under the normal incidence, a minimum insertion loss of 0.27 dB is achieved at a passband around 6 GHz, and the absorption bands with an absorption rate higher than 80% are 2.5 to 4.6 GHz in the lower band and 7.7 to 12 GHz in the higher band, respectively. Our results exhibit good agreements between measurements and simulations

A Measured Rasorber with Two Absorptive Bands

In this paper, a novel rasorber with both Frequency Selective Surface and absorptive periodical structure is developed. This rasorber works as a radome and an absorber. Firstly, the design procedure of the unit cell of this rasorber is explained. Then, the characteristics of the manufactured rasorber are measured. The characteristics include the transmission/reflection coefficients of the rasorber, the radiation properties of the horn antenna covered by the novel rasorber and the scattering features of this rasorber. In the passband, the gain of the antenna with our rasorber radome is only 1~2 dB lower than the one of the horn antenna without any radome. Furthermore, the radome has little effect on the radiation patterns of the horn antenna. In the absorptive bands of the rasorber, the electric level of the scattered electromagnetic wave from the rasorber can be 16.5 dB lower than the one from a metallic plane with the same size as the rasorber. The feature proves that this rasorber can be a good candidate in the stealth radar radome area

3-D Metamaterials: Trends on Applied Designs, Computational Methods and Fabrication Techniques

This work was funded in part by the Predoctoral Grant FPU18/01965 and in part by the financial support of BBVA Foundation through a project belonging to the 2021 Leonardo Grants for Researchers and Cultural Creators, BBVA Foundation. The BBVA Foundation accepts no responsibility for the opinions, statements, and contents included in the project and/or the results thereof, which are entirely the responsibility of the authors.Metamaterials are artificially engineered devices that go beyond the properties of conventional materials in nature. Metamaterials allow for the creation of negative refractive indexes; light trapping with epsilon-near-zero compounds; bandgap selection; superconductivity phenomena; non-Hermitian responses; and more generally, manipulation of the propagation of electromagnetic and acoustic waves. In the past, low computational resources and the lack of proper manufacturing techniques have limited attention towards 1-D and 2-D metamaterials. However, the true potential of metamaterials is ultimately reached in 3-D configurations, when the degrees of freedom associated with the propagating direction are fully exploited in design. This is expected to lead to a new era in the field of metamaterials, from which future high-speed and low-latency communication networks can benefit. Here, a comprehensive overview of the past, present, and future trends related to 3-D metamaterial devices is presented, focusing on efficient computational methods, innovative designs, and functional manufacturing techniques.Predoctoral Grant FPU18/01965BBVA Foundatio

Comparison between Frequency Selective Surfaces with Rectangular and Hexagonal Periodicity Operating as Absorbers

Two frequency selective surfaces operating as absorbers, with rectangular and hexagonal periodicity respectively, and relying on the same metal pattern in the unit cell are compared. The structures are implemented on an FR4 substrate, covered with copper metallization. The frequency responses (reflection coefficient) in normal incidence of electromagnetic waves and contents of higher order modes in the two cases are compared. Finally, the frequency response in oblique incidence of the hexagonal array is reported

Investigation of Radar Signal Interaction with Crossflow Turbine for Aviation Application

The increased adoption of wind energy is an important part of the push towards a net zero-emission economy. One obstacle that stands in the way of a higher rate of wind energy adoption is the interference that wind turbines cause to nearby radar installations. Wind turbines negatively affect the performance of nearby radar sites in a variety of different ways. Almost all types of radar are affected in at least one of these ways.In order to understand the degree to which an object such as a wind turbine interacts with radar, it is important to have detailed radar cross section (RCS) data for the object. In this work, a novel, low-cost, scale model radar cross section characterization system is presented with various advantages over traditional designs. This system was used to characterize the RCS of the novel Crossflow wind turbine. Additionally, work has been carried out on the characterization of metamaterial absorber coatings that can be applied to new and existing turbines for the purposes of reducing their radar cross section and the degree to which they cause radar inter-ference. The works presented can be leveraged to reduce concerns around radar interference from wind turbines, as well as to iteratively generate ge-ometries with lower radar cross sections for the aviation and infrastructure sectors, ultimately accelerating the pace of wind energy adoption and the move towards a net zero-emission economy

Cell miniaturization for x-band frequency selective surface

Electromagnetic Interference (EMI) generated by wireless devices can cause disturbance to electrical circuits. In this thesis, the Frequency Selective Surface (FSS) is proposed as the EMI shield for the interference control as it eliminates the need for power supply and blocking only the unwanted signals without interrupting the operation of other wireless devices. The contribution of this thesis comprise of the miniaturization technique employed for the dimension reduction of the unit cell FSS and the evaluation of the bending effect of the conformal FSS based on the semi-infinite modeling technique. All the designs and simulation works are completed utilizing the Computer Simulation Technology (CST) Microwave Studio software. First, the FSS is developed on the FR-4 substrate to perform as the band-stop planar FSS which support the attenuation over the X-band signals ranging from 8 GHz to 12 GHz. The evaluation of the planar FSS is performed using the unit cell boundary modelling. The miniaturization of the ring loop FSS is performed by adding four stubs at each 90° angle of the ring loop and four cross-dipole are embedded into convoluted ring loop FSS to further reduce the unit cell dimension. All the proposed unit cell geometries are modeled to accomplish the excellent transmission frequency response for normal and oblique incidence up to 60° cases at Transverse Electric (TE) and Transverse Magnetic (TM) polarizations. In order to ensure the FSS is competent to be employed as the EMI shield for the conformal structure, the proposed design is developed onto the flexible Polyethylene Terephthalate (PET) substrate. To prove the conformal suitability of the proposed planar design, the bending effects of the conformal FSS are investigated. The semi-infinite modeling allows modelling of the finite and infinite array in curved and uncurved directions, respectively. With the employment of this technique, the bending effects toward the performance of the proposed FSS at the normal angle of incidence for TE and TM polarizations are obtainable. From the results obtained, the convoluted ring loop FSS is the most sensitive to the bending effect while the ring loop FSS is the least sensitive to the bending effect. All the proposed FSS geometries are fabricated using either photolithography or inkjet printing technique. The manufactured prototypes are measured experimentally using bi-static measurement technique. All the proposed FSS provides minimum attenuation of - 25 dB at 10 GHz. The measurement results are shown to be similar with the simulation results. Hence, the proposed FSS can be employed in both planar and conformal structure

Recent Advances in the mm-Wave Array for Mobile Phones

With the development of communication system to the mm-wave band, the antenna design in the mm-wave band for mobile phones encounters new requirements and challenges. The mm-wave characteristics of short wavelength, high free-space path loss, and easy-to-be-blocking usually require mm-wave antennas with high gain and beam-scanning capability. Also, considering the very limited space occupied by antennas in mobile phones and the massive production of consumer electronics, small size, low cost, multiband, multi-polarization, and wide beam steering becomes the main key point of mm-wave array performance. In addition, as a special situation of the mobile antenna, the analysis of effect of the human tissue on the antenna performance is also important. So, in this chapter, a comprehensive summary on the recent advances in the mm-wave array for mobile phones including single-band, dual-band, and reconfigurable design of broadside array, horizontal polarized, vertical polarized, and dual-polarized design of endfire array, co-design of mm-wave array with lower band antenna, and user influence are summarized