Circular Polarization Selective Surface Research Articles

Wideband Dual-Circularly-Polarized Reflect-Arrays Based on Dual-Functional-Layer Cells With Berry-Phase Compensation at X-Band

We present the design and experimental validation of wideband dual-circularly-polarized (dual-CP) reflect-arrays (RAs) based on dual-functional-layered unit cells with independent control of circular polarizations. The proposed dual-CP RA cells comprise a circular polarization selective surface (CPSS) on the top based on a bandwidth-enhanced dual-meandered Pierrot structure that implements polarization selection of CP waves and a reflective half-wave plate (HWP) on the bottom. The dual-CP phase delay of the RA cells relies on the Berry-phase (BP) dictated by the rotation of the CPSS and HWP elements for achieving reflective beamforming of CP waves of opposite handedness. The diffractive properties of an infinite periodic gradient array of the dual-CP RA cells in a triangular lattice are investigated, which numerically verifies the dual-CP anomalous reflection capability. Two proof-of-concept RAs operating at X-band are designed, fabricated, and characterized. By replacing only the bottom functional layer of the RA, symmetrical and asymmetrically distributed dual-CP beams can be obtained. A measured peak gain of higher than 23.5 dBic is achieved, with a joint bandwidth of 11% for an axial ratio < 2 dB and a gain variation < 1 dB. The improved bandwidth performance, high-resolution BP compensation, and printed manufacturing process without using any metallic cavities make the demonstrated CPSS-based dual-CP RAs promising candidates for wireless and satellite communications.

A Contoured-Beam Reflector Satellite Antenna Using Two Doubly Curved Circular Polarization Selective Surfaces

We present antenna system using a circular polarization selective surface (CPSS) to realize a circular polarization (CP) equivalent to the widely used linear polarization (LP) gridded or dual-gridded reflector (DGR). The CPSS is realized by a multilayer stack of nonresonant anisotropic meander line surfaces, achieving a very wide bandwidth. The CPSS reflection and transmission dyadics are computed using full-wave simulations for all angles of incidence and design frequencies applicable, and the doubly curved reflector surface shapes are optimized in the TICRA POS software. The data are input to the TICRA tools software framework for antenna-system level radio frequency (RF) simulations. A planar CPSS sample was first manufactured and tested to demonstrate the adequacy of the selected multilayer design. A doubly curved reflector demonstrator based on the same technology and with a projected aperture of 750 mm was then designed, manufactured, and tested at Ku-band. While promising, the experimental results emphasize the difficulty of producing an electrically large multilayer doubly curved surface with RF performance equivalent to the original flat design and recommendations are provided to improve further the implementation of the proposed design.

On Computing the Mutual Coupling Between Two Antennas

The calculation of mutual coupling usually demands intense computations, especially for large aperture antennas placed in the near-field region of each other. In this article, the validity of an integral coupling formula is evaluated to demonstrate its utilizations where an efficient method for computing mutual coupling is most required. The integral coupling formula is used to compute the mutual coupling between two antennas in the near-field and far-field regions. The formula demonstrates fast and accurate computing properties based on typically available information such as 3-D vector far-field patterns and antenna configurations. Based on the coupling formula, a comprehensive evaluation is performed with respect to diverse antenna configurations, computation time, accuracy, and different polarizations. The expanded applicability of the formula is also examined through an antenna configuration, which includes a circular polarization selective surface (CPSS) structure to reduce the level of mutual coupling.

Dual-Mode Circular Polarization Selective Surface Cell for Single-Layer Dual-Band Circularly Polarized Reflectarray

A dual-mode circular polarization selective surface (CPSS) cell based on a modification of the Pierrot cell is presented for single-layer dual-band circularly polarized (CP) reflectarray antenna design. To achieve dual-mode CP discrimination performance, the improved three-dimensional geometry and the high-order resonances of the CPSS cell are utilized. The required phase shifts in both modes are obtained by varying the cell rotation angle. A single-layer dual-band reflectarray operating with orthogonal CPs has been fabricated and tested. Measured results show the peak gains of 25.2 dBi at 11.6 GHz with 31% 3 dB axial ratio (AR) bandwidth and 26.5 dBi at 14.6 GHz with 32% 3 dB AR bandwidth, respectively. The measured efficiency is 41.2% at 11.6 GHz and 55.5% at 14.6 GHz.

A Thin and Broadband Linear-to-Circular Polarizer Based on Grid-Patch Structure for Ku-Band

A three-layer circular polarization selective surface operating in Ku-band is proposed in this communication. We design a thin grid-patch structure to achieve linear-to-circular polarization transformation over a wide frequency band. The periodic structure could be analyzed via equivalent circuit model theory. Numerical simulations have been carried out and the prototype structures have been fabricated and experimentally validated. The axial ratio (AR) of the transmitted field remained below 3 dB over the entire bandwidth, and the 3 dB AR bandwidth is approximately 44.6%. The design has a subwavelength thickness of 6 mm (0.28λc). Besides, this design could be also applied to beam scanning antennas because of its capability in condition of large oblique incidence angle (±50 deg).

Design and Demonstration of Impedance-matched Dual-band Chiral Metasurfaces

We propose a new family of impedance-matched chiral metasurfaces that offer arbitrary polarization control at two different frequencies. To this end, two main problems are addressed: (1) determination of the required surface impedances for a certain user-defined chiral functionality at two frequencies and (2) their physical realization at microwaves. The first milestone is achieved through a proposed synthesis method that combines a semi-analytical method and a nonlinear optimization technique. In particular, the impedances are computed such that the devised chiral metasurface is also impedance-matched to a terminating medium. The chiral metasurfaces are then physically realized at microwaves by cascading layers of rotated arrays of multiple concentric rectangular copper rings. We establish that these proposed unit cells offer distinct dual-resonances that can be arbitrarily and independently tuned for two orthogonal linear polarizations at each of the two operating frequencies. This allows simultaneous physical mapping of the required surface impedances at two frequencies. The versatility and generality of the proposed numerical and physical solutions are demonstrated through two design examples: A dual-band circular polarization selective surface (CPSS) and a dual-band polarization rotator (PR). The dual-band CPSS is further confirmed experimentally at 20 GHz and 30 GHz based on a free-space quasi-optical system.

Coupled Split-Ring Resonator Circular Polarization Selective Surface

A novel class of circular polarization selective surfaces (CPSSs) consisting of a pair of planar split-ring resonator arrays is proposed. A significant advantage of the proposed structure over existing designs is its manufacturing simplicity compatible with standard printed technology processes. Its operating principle is reviewed alongside that of the Pierrot cell and in light of the linear polarization reflection and transmission characteristics of CPSSs. Guidelines for the initial design of the proposed CPSS concept are thus derived. Further design considerations and tradeoffs are also discussed. The validity of the concept is confirmed by means of a design example entailing a right-hand CPSS at 20 GHz. Full-wave simulation results and experimental testing on a fabricated prototype are presented and agree well with the theoretical predictions.

Highly efficient all-dielectric optical tensor impedance metasurfaces for chiral polarization control.

We propose a highly efficient (nearly lossless and impedance-matched) all-dielectric optical tensor impedance metasurface that mimics chiral effects at optical wavelengths. By cascading an array of rotated crossed silicon nanoblocks, we realize chiral optical tensor impedance metasurfaces that operate as circular polarization selective surfaces. Their efficiencies are maximized through a nonlinear numerical optimization process in which the tensor impedance metasurfaces are modeled via multi-conductor transmission line theory. From rigorous full-wave simulations that include all material losses, we show field transmission efficiencies of 94% for right- and left-handed circular polarization selective surfaces at 800 nm.

A broadband, circular-polarization selective surface

We introduce a new technique for designing wideband circular-polarization selective surfaces (CPSSs) based on anisotropic miniaturized element frequency selective surfaces. The proposed structure is a combination of two linear-to-circular polarization converters sandwiching a linear polarizer. This CPSS consists of a number of metallic layers separated from each other by thin dielectric substrates. The metallic layers are in the form of two-dimensional arrays of subwavelength capacitive patches and inductive wire grids with asymmetric dimensions and a wire grid polarizer with sub-wavelength period. The proposed device is designed to offer a wideband circular-polarization selection capability allowing waves with left-hand circular polarization to pass through while rejecting those having right-hand circular polarization. A synthesis procedure is developed that can be used to design the proposed CPSS based on its desired band of operation. Using this procedure, a prototype of the proposed CPSS operating in the 12–18 GHz is designed. Full-wave electromagnetic simulations are used to predict the response of this structure. These simulation results confirm the validity of the proposed design concept and synthesis procedure and show that proposed CPSS operates within a fractional bandwidth of 40% with a co-polarization transmission discrimination of more than 15 dB. Furthermore, the proposed design is shown to be capable of providing an extremely wide field of view of ±60°.

A Circular Polarization Selective Surface for Space Applications

In this paper, an LHCPSS based on the Pierrot cell has been theoretically studied and demonstrated experimentally. Design guidelines are given and an accurate fabrication process has been developed. Measurements of a fabricated prototype exhibit performance compliant with the requirements for space applications over a limited bandwidth. Axial ratio and insertion loss smaller than 1 and 0.5 dB, respectively, over a 7% bandwidth have been achieved at 9.8 GHz. Wider bandwidths with low axial ratio are possible by relaxing the requirements in terms of insertion loss.

Tunable circular polarization selective surfaces for low-THz applications using patterned graphene.

This paper demonstrates a new type of frequency tunable polarization selective surface operating at low THz, which is devised by utilizing the unique features of graphene. The device is comprised of an infinite array of identical unit cells in three layers. Multiple graphene dipoles are placed on the top and bottom layers to form the vertical and horizontal electric field filters. Using this new configuration, the proposed device exhibits reflection for the incident Left-Hand-Circular-Polarization (LHCP) waves and becomes transparent to the incoming Right-Hand-Circular-Polarization (RHCP) waves. The excited localized surface plasmonic resonance mode on the graphene based unit cells significantly reduces the physical dimension of the device. The unit cell dimension of the proposed design is in the order of 0.18 wavelengths in comparison to conventional metallic structures, where it is of order a half a wavelength. In the full wave analysis, the graphene based polarization selective surfaces exhibit an isolation of 21 dB for LHCP waves and a transmission loss of around 5.1 dB for waves with RHCP characteristics. The performance has also been examined under oblique incidence. The results fully verify that the proposed planar device operates properly for incident angles up to 40°. The tuning effect of the described device is investigated by varying the chemical potentials of graphene. Significant frequency reconfiguration capability is achieved in the isolation of LHCP incident waves, and meanwhile, for RHCP incidence, the transmission rate remains reasonably high.

Design And Measurement of Tensor Impedance Transmitarrays For Chiral Polarization Control

Tensor impedance transmitarrays consist of tensor impedance surfaces, separated by dielectric spacers. In this paper, we present a design method for realizing tensor impedance transmitarrays that are capable of controlling the reflection and transmission of circularly polarized waves, referred to as chiral polarization control. To achieve this, we implement a multi-conductor transmission-line (MTL) model to characterize how vertically and horizontally polarized waves are transmitted and reflected through the surface and to synthesize the desired tensor impedances, which comprise the array. Using this MTL model, we show how to synthesize two different chiral transmitarrays. This includes a polarization rotator, which rotates any linear polarization by 90 $^{\circ}$ and a circular polarization selective surface (CPSS), which transmits one hand of circular polarization while reflecting the other. This is verified with full-wave simulation showing that our proposed model works. We also fabricate and measure the CPSS at X-band based on our design procedure. To measure the CPSS, we use a novel four-port quasi-optical system to characterize both the reflection and transmission of vertically and horizontally polarized fields off of the surface. We achieve a good agreement with our simulated results though we have $-{\hbox{1.7 dB}}$ more loss than expected due to the use of FR-4 as our substrate.

Alternative Topologies of Circular Polarization Selective Surfaces Based on Modifications of the Pierrot Cell

Circular polarization selective surfaces (CPSS) based on two variants of the original Pierrot cell are proposed. For the first variant, which uses a load in the middle segment, it is possible to equalize the frequencies at which the reflection and transmission performance for the two orthogonal circular polarizations is optimal. The second variant is a double Pierrot cell having a twofold rotation symmetry, which leads to an increased bandwidth and less sensitivity to variations in the angle of incidence. Experimental results in good agreement with full wave simulations are presented. The printed circuit board (PCB) fabrication process used with flexible substrates allows more freedom for adjusting the cells in order to improve the performance and the bandwidth of the CPSS.

A Circular Polarization Selective Surface Implemented on a Flexible Substrate

A new technique to realize a circular polarization selective surface (CPSS) implemented with Pierrot cells is proposed. This technique uses a folded flexible substrate, which enables the implementation of the 3D Pierrot cells on a single metal layer defined with precision printed circuit board techniques, without the need for metallized via holes. A left-hand CPSS is designed to illustrate the benefits of the proposed approach. For the fabricated prototype, the measured characteristics at normal incidence are in good agreement with simulations results obtained with HFSS. It is shown that compared to other Pierrot cell designs presented in the literature, this new approach simplifies the fabrication process while giving similar performance.

Design and Analysis of a Cascade Circular Polarization Selective Surface at K Band

This paper proposes a circular polarization selective surface (CPSS) design consisting of two meander-line circular polarizers and a linear polarizer. No vias are required. These polarizers are individually designed with ANSYS-HFSS (High Frequency Structure Simulator) software whereas the response of the overall cascade CPSS is computed with the GSM approach. A cascade CPSS which includes three-layer meander-line polarizers is designed and fabricated. Good agreement is shown between experimental and simulated results, with only the TE00 and TM00 modes in the GSM analysis. Finally, analysis of the circular polarizers based on simple filter theory is done to better understand how the performance of the whole structure can be improved.

Unit Cell for Reflectarrays Operating With Independent Dual Circular Polarizations

A unit cell for dual-circularly-polarized (CP) re- flectarrays illuminated by a dual-CP primary feed is designed and validated experimentally around 8.5 GHz. It is composed of two layers reflecting independently and simultaneously the two incident circular polarizations. The first layer is a circular polarization selective surface (CPSS) based on an enhanced version of the original Pierrot’s cell with multiple wires bent in a crank-like shape. The second layer is made of dipoles printed on a grounded substrate; it is used to reflect the incident right-hand CP (RHCP) wave transmitted through the CPSS with a 2-bit phase resolution. This letter demonstrates that the sole association of both layers is not sufficient to reach the expected behavior. An additional optimization step is required to cancel out uncontrolled reflections and improve isolation between both polarizations. The simulated and measured characteristics are in good agreement for the two circular polarizations

INVESTIGATION ON USING CPSS ELEMENTS IN DUAL CIRCULAR POLARIZATION REFLECTARRAY ANTENNAS

In this paper, properties of three types of Circular Polarization Selective Surface (CPSS) cells including Pierrot, Morin, and Tilston, for using in dual circular polarization reflectarray antenna design are investigated. First they are designed for a center frequency about 10GHz, and circular polarization properties including Reflection Loss, Transmission Loss, Reflected Axial Ratio, and Transmitted Axial Ratio are calculated and presented. Finally, reflection phase curves are presented, and the comparison between simulated properties is accomplished. Simulations show that Tilston cell is more optimum in dual circular polarization reflectarray antennas.

Synthesis of Polarization Transformers

We study the possibility of analytically synthesizing different polarization-transforming devices realized as arrays of small particles. The proposed method is based on general relations between the reflection and transmission coefficients and the polarizabilities of arbitrary bi-anisotropic particles. As an example, we reveal all possible types of inclusions which can be used to realize twist polarizers, select one of them and synthesize a novel twist polarizer. The synthesized twist polarizer is then fitted on a standard printed circuit board, optimized numerically, and finally manufactured and measured. The experimental results for the twist polarizer show good correspondence with the simulations and the new method is found to be a useful tool for developing any polarization-transforming devices. As one more example, a novel circular polarization selective surface is synthesized.

A New Advance in Circular Polarization Selective Surface—A Three Layered CPSS Without Vertical Conductive Segments

Investigations into a surface that reflects one sense of circularly polarized electromagnetic wave but transmits the other, namely a circular-polarization selective surface (CPSS), were carried out. This paper presents CPSS using simple planar structure without any vertical conductive segments. Couplings, through the use of L-shaped traces, were produced to replace the vias. Operational principle and design procedure are developed, thus the optimal design parameters are found. Also presented are the results of numerical computations and measurements for "isolation" and "transmission loss". A 30 GHz example demonstrates the performances of the design and the attractiveness in millimeter-wave circular polarization selectivity applications

Generalized scattering matrix and symmetry principles for infinite planar structures

This paper presents a technique for determining the scattering coefficients of the Generalized Scattering Matrix (GSM) for an infinite planar structure whose operation is prescribed. The technique is partly a synthesis tool in that it allows to identify some geometrical properties of the structure from the relationships between various coefficients of the GSM. These relationships are cast into a formalism that simplifies and generalizes the development of many previously reported results. We also apply the technique to various structures for the purpose of demonstrating its use and validity. When this technique is applied to Linear or circular polarizers with the GSM incorporating only the dominant mode, we find that ideal polarizers are possible only at normal incidence, regardless of their specific physical realizations. Similarly, we find that a structure corresponding to the reciprocal circular polarization selective surface must satisfy the property of 2-fold rotational symmetry, except in a limited neighborhood of the normal incidence where the property of reciprocity suffices, and must not satisfy the property of longitudinal reflection symmetry.