Reflectarray Design Research Articles

Efficient General Reflectarray Design and Direct Layout Optimization with a Simple and Accurate Database Using Multilinear Interpolation

In this work, a simple, efficient and accurate database in the form of a lookup table to use in reflectarray design and direct layout optimization is presented. The database uses N-linear interpolation internally to estimate the reflection coefficients at coordinates that are not stored within it. The speed and accuracy of this approach were measured against the use of the full-wave technique based on local periodicity to populate the database. In addition, it was also compared with a machine learning technique, namely, support vector machines applied to regression in the same conditions, to elucidate the advantages and disadvantages of each one of these techniques. The results obtained from the application to the layout design, analysis and crosspolar optimization of a very large reflectarray for space applications show that, despite using a simple N-linear interpolation, the database offers sufficient accuracy, while considerably accelerating the overall design process as long as it is conveniently populated.

Designing Wideband Microstrip Reflectarrays for 10 GHz

This paper presents two microstrip reflectarray designs based on variable size unit cells for 10 GHz. One design uses a 3-layer unit cell with polygon shaped patch and the other uses a unit cell with 1-layer square loop patch. Both arrays have a size of 10λ × 10λ at 10 GHz, can reflect the incoming wave as a high gain pencil beam in the desired direction of θ = 30°. Gains at 10 GHz are 23.6 dB and 26.1 dB for the 3-layer and one-layer structures, respectively. The multi-layer structure resulted in a wider gain banwdith. Simulation results show that the 3-dB gain bandwdith is about 22% for the 3-layer structure reflectarray, as compared to 12% for the one-layer structure

Synthesis and design of plane reflectarrays of microstrip elements for scanning antenna systems of the 60 GHz band

Synthesis and design of plane reflectarrays of microstrip elements for scanning antenna systems of the 60 GHz band

Shaped-Pattern Reflectarray Antennas for mm-Wave Networks Using a Simple Cell Topology

In this paper, it is proposed the use of ultra-thin reflectarrays in some emerging scenarios in the new mm-wave cellular networks such as 5G, Beyond-5G (B5G), and future 6G. To that purpose, two dual-linear polarization reflectarrays are developed to provide coverages in different scenarios at the mm-waves band. Working at 28 GHz, reflectarray designs adapt the radiated field to the coverage area specified in each scenario, through an ultra-thin surface composed of simple cells. To evaluate the antenna performance, two reflectarray prototypes identical in size are manufactured and tested achieving a good trade-off between the performance and the low-cost, low losses and, low-profile characteristics of the antenna. This work demonstrates the good performance of simple topology reflectarrays, being an interesting antenna candidate in the upcoming wireless networks.

A novel broadband reflectarray for 5G satellite communications

The design, fabrication, and experimental validation of wideband reflectarray with concentric coupled half-square rings operating at 26.5 GHz for 5G communication is presented in this paper. The proposed unit cell has a simple square patch enclosed within the coupled half-square rings. The varying delay line length attached to the outer ring provides a phase variation of 420°. A center-fed reflectarray antenna constructed with circular geometry (12.6 diameters) using 413 elements offers a measured gain of 27.1 dBi and 51.25% of aperture efficiency at its center frequency. The measured 3- and 1-dB gain bandwidth of 45% and 28.6% along with a side lobe level (SLL) of −17.6 dB are achieved. The measured cross-polarization level is less than −28 dB. Thus, the proposed wideband reflectarray has evolved into a provocative candidate for applications like base station antennas in earth exploration satellites, mobile base station satellites, and radio astronomy satellites.

Enhanced Efficiency and Reduced Side Lobe Level Convex Conformal Reflectarray

In this work, the design of a convex conformal reflectarray (CRA), suitable to be used for high gain on board antenna in mobile communication systems, is presented. The reflector is not planar, as in usual reflectarray configurations, but the re-radiating elements are printed on a surface conformed to a cylinder to mimic a curved surface, such as the fuselage of an airplane, on which the reflectarray could be mounted. To compensate for the loss in efficiency due to the curvature, an ad hoc feed is designed; the results obtained with the simulation of the entire structure and the measurements of its prototype prove the effectiveness of the design procedure and its capability in enhancing the CRA features, in comparison with similar but more conventional solutions.

A HIGH GAIN AND HIGH BANDWIDTH REFLECTARRAY ANTENNA FOR 5G COMMUNICATION

This paper presents the design of high gain and bandwidth reflectarray for 5G networks operating in Millimeter-wave (mmWave) at 28GHz and 38GHz. A polymer benzocylobutene (BCB) is used as substrate material having a dielectric constant of 2.65, and low tan δ ≤ 0.0008. The unit cell is optimized to achieve full phase reflection of 334o over the operating band. Enhanced gain, wider bandwidth and full phase reflection are achieved by making air holes in the substrate. A 15×15 elements reflectarray based on the optimized unit cell is designed to enhance the gain. The reflectarray is excited through horn feed having a gain of 15dB with a feeding distance of 165mm and 00 offsets. A gain of 23dB was observed at lower operating frequency (i.e 28GHz) and 25dB at upper operating frequency (i.e 38GHz)with a bandwidth of 2GHz at both operating frequencies.

Shaped-Beam Reflectarray Design by Means of Social Network Optimization (SNO)

In this work, an innovative approach for the design of a shaped-beam reflectarray (RA) is presented. It is based on the use of a novel evolutionary algorithm (EA), named Social Network Optimization (SNO), that presents good capabilities in terms of convergence and reliability, and therefore it is suitable for optimizing a complex problem such as the one of interest. The full-wave analysis of a small–medium configuration designed with the proposed approach and the experimental characterization of a prototype proved the effectiveness of the adopted method.

Design of Dual-Polarized Reflectarray for Near-Field Shaped Focusing

This letter presents a design of reflectarray for near-field (NF) shaped focusing, and a synthesis method is proposed to generate desired shaped pattern in the NF zone. The orthogonally arranged tridipoles structure is used to realize the dual-polarized reflectarray. The unit cell has continuous reflection phase-shift ranges (more than 360°) under <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> -polarized and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> -polarized incident E-fields. A sample reflectarray generating dual-polarized focused patterns is presented to validate the design. Experimental results show that the horizontal component of E-field has the shaped pattern of letter “X,” and the vertical component of E-field owns the shaped pattern of letter “Y.” Besides, the measured results are in good agreement with the theoretical analyses.

Hybrid Polarization-Phase Tuning Methodology for Reflectarray Antennas

A hybrid polarization-phase tuning methodology is presented for reflectarray antenna designs. First, three representative phasing approaches for reflectarray designs are briefly reviewed, and it is pointed out that when the polarization conversion is considered, these phasing approaches can be combined together to achieve more versatile functionalities and better performance. It is theoretically derived that using the mirror combining approach (MCA), broadband reflectarray elements with polarization conversion can be achieved. Using the rotational combining approach (RCA), both amplitude and phase of the reflected cross-polarization waves can be controlled. Next, a split ring element has been designed as an example to demonstrate the theoretical analysis. By using the MCA, the designed element achieves a linear 360° phase coverage, which suggests its capability of wideband operation. By using the RCA, the designed element achieves continuous amplitude modulation from 0 to 1 and full 360° phase coverage. Finally, a Ka-band reflectarray prototype with broadband behavior is designed, fabricated, and measured. It has achieved high-gain pencil beams pointing at predesigned directions. The measured gain at 20 GHz is 35.6 dBi with the aperture efficiency of 54.4% under linear-polarization (LP) excitation, and the gain is 35.4 dBi with the aperture efficiency of 52% under circular-polarization (CP) excitation. The measured 1 dB gain bandwidth is 18.5% (19-22.7 GHz) and 12.5% (19.3-21.8 GHz) under LP and CP excitation, respectively.

Reconfigurable Reflectarray Antenna: A Comparison between Design Using PIN Diodes and Liquid Crystals

This work presents the design and analysis of active reflectarray antennas with slot embedded patch element configurations within an X‐band frequency range. Two active reflectarray design technologies have been proposed by digital frequency switching using PIN diodes and analogue frequency tuning using liquid crystal‐based substrates. A waveguide simulator has been used to perform scattering parameter measurements in order to practically compare the performance of reflectarray designed based on the two active design technologies. PIN diode‐based active reflectarray unit cell design is shown to offer a frequency tunability of 0.36 GHz with a dynamic phase range of 226°. On the other hand, liquid crystal‐based design provided slightly lower frequency tunability of 0.20 GHz with a dynamic phase range of 124°. Moreover, the higher reflection loss and slow frequency tuning are demonstrated to be the disadvantages of liquid crystal‐based designs as compared to PIN diode‐based active reflectarray designs.

Development of a Pin Diode-Based Beam-Switching Single-Layer Reflectarray Antenna

This paper presents a practical demonstration for the design and development of a switchable planar reflectarray using PIN diodes in the X-band frequency range. Waveguide scattering parameter measurements for the unit cells and far-field measurements of the periodic reflectarrays have been carried out to verify the predicted results. Reflectarray unit cell measurements demonstrated a frequency tunability of 0.36 GHz with a dynamic phase range of 226°. On the other hand, the designed 6 × 6 periodic reflectarray has been shown to achieve beam switching from +6° to −6° with different switching states of PIN diodes. This type of beam switching can be used in satellite communication for specific region coverage.

Systematic Study of the Influence of the Angle of Incidence Discretization in Reflectarray Analysis to Improve Support Vector Regression Surrogate Models

A systematic study concerning the discretization of the angle of incidence in surrogate models obtained with support vector regression (SVR) is presented. The problem addressed in this work arises from the dependence of the reflection coefficients on the angle of incidence. While the direct coefficients are usually stable with the angle of incidence, this is not the case with the cross-coefficients, which translates this behavior to the crosspolar component of the radiation pattern. Then, correctly assessing this influence and minimizing radiation pattern distortion allow training SVR surrogate models per angle of incidence without penalizing accuracy in the prediction of the far field. The results shown in this work are directly relevant to improving the computational performance of SVRs applied to reflectarray design since they allow reducing the dimensionality of the models by generating surrogate models per angle of incidence instead of including the angles of incidence as input variables. In addition, it highlights the importance of a proper discretization of the angles of incidence for a correct prediction of the crosspolar pattern for its subsequent optimization, especially for advanced space applications with tight crosspolar requirements.

Comparison between Specialized Quadrature Rules for Method of Moments with NURBS Modelling Applied to Periodic Multilayer Structures

A comparison between Ma-Rokhlin-Wandzura (MRW) and double exponential (DE) quadrature rules for numerical integration of method of moments (MoM) matrix entries with singular behavior is presented for multilayer periodic structures. Non Uniform Rational B-Splines (NURBS) modelling of the layout surfaces is implemented to provide high-order description of the geometry. The comparison is carried out in order to show that quadrature rule is more suitable for MoM matrix computation in terms of sampling, accuracy of computation of MoM matrix, and CPU time consumption. The comparison of CPU time consumption shows that the numerical integration with MRW samples is roughly 15 times faster than that numerical integration using DE samples for results with similar accuracies. These promising results encourage to carry out a comparison with results obtained in previous works where a specialized approach for the specific analysis of split rings geometries was carried out. This previous approach uses spectral MoM version with specific entire domain basis function with edge singularities defined on split ring geometry. Thus, the previous approach provides accurate results with low CPU time consumption to be compared. The comparison shows that CPU time consumption obtained by MRW samples is similar to the CPU time consumption required by the previous work of specific analysis of split rings geometries. The fact that similar CPU time consumptions are obtained by MRW quadrature rules for modelling of general planar geometries and by the specialized approach for split ring geometry provides an assessment for the usage of the MRW quadrature rules and NURBS modelling. This fact provides an efficient tool for analysis of reflectarray elements with general planar layout geometries, which is suitable for reflectarray designs under local periodicity assumption where a huge number of periodic multilayer structures have to be analyzed.

Transmit–Receive Parabolic Reflectarray to Generate Two Beams per Feed for Multispot Satellite Antennas in Ka-Band

This contribution describes the design of a multibeam parabolic reflectarray to produce two adjacent beams per feed in orthogonal circular polarization (CP) simultaneously at the transmission (Tx) and reception (Rx) frequencies in the Ka -band. The variable rotation technique (VRT) has been applied to the reflectarray cells based on two types of resonant elements, which makes it possible to provide orthogonal beams at Tx and Rx, as well as to implement an in-band optimization procedure to reduce the cross-polarization. A 90 cm parabolic reflectarray has been designed, manufactured, and tested to produce multiple adjacent beams in RHCP and LHCP at both 20 and 30 GHz. The results are satisfactory and validate the concept of generating two spaced beams in the orthogonal CP by a single feed, changing the polarization of the beam between Tx and Rx. This concept can be suitable for multispot satellites in the Ka -band, enabling to halve the number of onboard antennas and feeds.

Design and analysis of dual-polarized reflectarray with low sidelobe level for wireless communication applications

Design and analysis of dual-polarized reflectarray with low sidelobe level for wireless communication applications

On the Use of the Angle of Incidence in Support Vector Regression Surrogate Models for Practical Reflectarray Design

A common approach in the literature when obtaining surrogate models of reflectarray unit cells is to include, among other variables, the angles of incidence as input variables to the model. In this work, we use support vector regression (SVR) to compare this approach with a new strategy which consists in grouping the refletarray elements under a small set of angles of incidence and train surrogate models per angle of incidence pair. In this case, the dimensionality of the SVR decreases in two with regard to the former approach. In both cases, two geometrical variables are considered for reflectarray design, obtaining 4-D and 2-D SVRs, respectively. In contrast to the common approach in the literature, the comparison between the 4-D and 2-D SVRs shows that a proper discretization of the angles of incidence is more competitive than introducing the angles as input variables in the SVR. The 2-D SVR offers a shorter training time, faster reflectarray analysis, and a similar accuracy than the 4-D SVR, making it more suitable for design and optimization procedures.

Design of a single-layer broadband reflectarray using circular microstrip patch loaded with two unequal slots

A linearly polarized single-layer single-resonator reflectarray, which is designed using a simple circular patch loaded with two unequal rectangular slots, is investigated for the first time. For the proposed design, the linearity and sensitivity of the phase curve (S-curve) can be easily optimized by adjusting the ratio of the two unequal slots changeable according to a simple design equation. Here, the patch radius serves as a phase-shifting geometrical parameter and it is able to achieve a wide phase range of more than 458° with low phase sensitivity and a low reflection loss of less than 0.5 dB. With the use of the optimized phase curve, an offset-fed 13 × 13 full-fledged reflectarray with a square aperture is designed, fabricated and measured. Measurement results show that a −1-dB gain bandwidth of 11.8% and an antenna gain of 23.4 dBi are realizable at the center frequency of 9.3 GHz. Also, the proposed reflectarray has an aperture efficiency of 42% and a radiation efficiency of 98%. The proposed reflectarray has a simple structure and it is able to achieve smooth phase curve, low cross-polarized radiation field and low sidelobes.

Perfectly Reflecting Metasurface Reflectarrays: Mutual Coupling Modeling Between Unique Elements Through Homogenization

This article presents a new technique for the accurate design of metasurface reflectarrays. The design technique accounts for mutual coupling between distinct reflectarray elements. Contrary to the conventional approach, no local periodicity assumptions are made in the design of the reflectarray elements. The reflectarray considered consists of a subwavelength-patterned metallic cladding (metasurface) over a ground plane. The cladding is homogenized and modeled as an inhomogeneous impedance sheet. The inhomogeneous impedance sheet is designed through the solution of an integral equation. The integral equation is solved using the method of moments. In the design, both the scattered field amplitude and phase are specified. The scattered field amplitude is chosen to conserve local power density at the reflectarray surface. This condition results in complex sheet impedances. An optimization technique is subsequently used to obtain a purely reactive sheet which gives the same performance as the complex sheet. The process used to extract the reactance of printed geometries is detailed. An example of a $20 \lambda $ wide array is presented. All the results are validated through COMSOL Multiphysics simulations. The presented design approach is compared to the conventional approach and is shown to more accurately predict the far-field patterns of a reflectarray.

Efficient analysis method and design approach for broadband reflect‐arrays with isotropic/artificial anisotropic substrates

Plane-wave scattering by metallic grating with artificial anisotropic substrate is a problem solved in this study for the design of broadband reflectarrays. For determination of the reflection characteristics of such structures, a generalised transmission line modelling is used for evaluating the dyadic Green's function. This function is utilised in a summation equation used for calculating the induced electric currents on the reflectarray's metallic grating. For solving the obtained summation equation, the Periodic Method of Moments with Galerkin procedure is applied. Such an analysis method helps to compute the phase diagram needed to design of reflectarray. The efficiency of this method is assessed by considering its cost-time and rate of convergence versus space harmonics. In the design step, a new phase realisation approach is implemented for minimising the frequency dispersion's adverse effects. This approach optimises the arrangement of metallic elements on the reflectarray's aperture and decreases the dependency of broadband reflectarray design to the element phase behaviour. As a result, this technique leads to lower side lobe level and better frequency response than traditional approaches. To verify the results of the developed solution, two different broadband reflectarrays for X- and Ku-bands are fabricated and measured.