Search

This article presents a 3-D polarizing screen that converts linear to circular polarization in a broadband frequency range. The conceived unit cells are fully metallic and based on structures that support transverse electromagnetic modes. Such cells have been specially conceived to be manufactured through metal 3-D printing based on selective laser melting. This is the first time that a polarizing structure presents such a broadband behavior without the use of dielectric materials. In addition, this is the first successful proof of concept of additive manufacturing in the context of metallic periodic surfaces, which is enabled by the use of a codesign approach. The present proposal is validated through the design and manufacturing of a prototype operating in K- and Ka-bands. Successful experimental results are reported. [ABSTRACT FROM AUTHOR]

The concept and development of a highly efficient pyramidal horn is described. The radiating element comprises a rectangular radiating aperture fed by two smaller flared square waveguide sections via a bifurcated H-plane surface discontinuity. For the simultaneous feeding of the two-port radiating element, the total antenna includes a compact H-plane power divider. Properly weighted TE $_{n0}$ modes ($n\in N^{\ast }$) are excited at the output of the two flared waveguide sections. The bifurcation is responsible for the recombination of the incoming fields. The low-dispersive modal coupling coefficients (or transmission coefficients of the bifurcation’s generalized scattering matrix) between the excitation and the aperture modes enable the broadband realization of the targeted aperture modal content. The common waveguide section is responsible for the phase alignment of the aperture modes. The design method targets a preoptimized model, which approximates the amplitude of the aperture modes TE $_{m0}$ ($m = 1, 3, 5, \ldots $) in the order of 1/ $m$ and minimizes their relative phase difference. Finally, maximum aperture efficiency can be achieved by fine tuning and with low computational complexity. Design principles are given and illustrated by means of an example involving an antenna with aperture size of about $2.8\lambda _{0} \times 1.4\lambda _{0}$ ($\lambda _{0}$ is the free-space wavelength at the central frequency of operation). The antenna exhibits aperture efficiency levels above 95% over the entire Ku-Tx-band (10.7–12.75 GHz), as well as a compact profile ($4.1\lambda _{0}$). The measured results of a prototype manufactured through milling verify experimentally the numerically predicted performance. [ABSTRACT FROM AUTHOR]

A variety of cell elements are presented in this paper for the construction of frequency selective surface (FSS) backed reflectarrays. Among the cell elements are the conventional ring elements for FSS and slotted patch for the reflectarray. Different combinations of FSS cell elements and reflectarray cell elements are employed for the realization of FSS-backed reflectarrays and the criteria for the selection of the optimum structure are presented. Prototypes of these reflectarrays were fabricated and tested. The measurements demonstrated that for an optimum design, the gain of an FSS-backed reflectarray is about 1.0 dB lower than its counterpart backed by solid ground plane. Characterization of the out of band performance of these antennas demonstrated close to 1.0 dB insertion loss. Index Terms--Frequency selective surfaces (FSSs), quasi-optical measurement systems, reflectarray antennas.

Two new compact lens antenna configurations are presented and compared for data link communications with LEO satellites at 26 GHz. These lenses match a secant type radiation pattern template in the elevation plane while having a mechanically scanned sector beam in azimuth to enhance gain as much as possible. No rotary joints or multiple feeds are required and emphasis is put also on the compactness of the proposed solutions (< 6[[lambda].sub.o]). Two alternative lens configurations are evaluated numerically and experimentally: one is based on modified axial-symmetric dome lens geometry, and the other one consists of a full 3-D double-shell lens antenna. In contrast to current nearly omnidirectional antennas, the directivity of our lens prototypes is above 15.4 dBi. Up to 4.2 dB loss obtained in the prototypes can be significantly reduced by using lower loss dielectrics and matching layers, without affecting the conclusions. The numerical and experimental results are in good agreement with the radiation specifications given the compact size of the antennas. Index Terms--Beam shaping, compact lens antennas, constant flux illumination, scanning antennas.

A breadboard of a three-layer printed reflectarray for dual polarization with a different coverage in each polarization has been designed, manufactured, and tested. The reflectarray consists of three layers of rectangular patch arrays separated by a honeycomb and backed by a ground plane. The beam shaping for each polarization is achieved by adjusting the phase of the reflection coefficient at each reflective element independently for each linear polarization. The phase shift for each polarization is controlled by varying either the x or y patch dimensions. The dimensions of the rectangular patches are optimized to achieve the required phase shift for each beam at central and extreme frequencies in the working band. The reflectarray has been designed to produce a contoured beam for a European coverage in H-polarization in a 10% bandwidth, and a pencil beam to illuminate the East Coast in North America in V-polarization. The measured radiation patterns show that gain requirements are practically fulfilled in a 10% bandwidth for both coverages, and the electrical performances of the breadboard are close to those of a classical dual gridded reflector. Index Terms--Contoured beam, dual gridded reflector, dual polarization, multilayer, printed arrays, reflectarray.

A scale changing approach is proposed for the electromagnetic modeling of phase-shifter elements used in reconfigurable microelectromechanical system (MEMS)-controlled reflectarrays. Based on the partition of the discontinuity plane in planar sub-domains with various scale levels, this technique allows the computation of the phase shift from the simple cascade of networks, each network describing the electromagnetic coupling between two scale levels. The high flexibility of the approach associated with the advantages of the integral equations formulations renders this original approach powerful and rapid. The scale-changing technique allows quasi-instantaneous computing of the 1024 phase shifts achieved by ten RF-MEMS switches distributed on the phase-shifter surface. Moreover, the proposed approach is much better than the finite-element-method-based software in time costing. Experimental data are given for validation purposes. Index Terms--Multiscale structures, planar phase shifter, reflectarrays, RF microelectromechanical systems (MEMS).

We report the design of a directive antenna using the electromagnetic resonances of a Fabry-Perot cavity. The Fabry-Perot cavity is made of a ground plane and a single metallic grid. The resonance is excited by a patch antenna placed in the cavity at the vicinity of the ground plane. The two remarkable features of Fabry-Perot cavity antennas are, first, that they are very thin and second that only one excitation point is needed. A directivity of about 600 is measured at f = 14.80 GHz which is to our knowledge one of the highest directivities reported for an antenna using Fabry-Perot resonances. Index Terms--Directive antennas, Fabry-Perot resonators, leaky wave antennas.

This article presents a parallel-plate lens beamformer for continuous wide-angle scanning. The design is based on a compact dual-lens system with extended scanning range and is optimized using a previously developed geometrical optics technique. Beam steering is accomplished with a mechanical feed system based on the noncontact characteristic of groove gap waveguides, offering large bandwidth, low profile, and mechanical ruggedness. The proposed concept is validated by an all-metal prototype of a $20.5\lambda $ lens operating in the uplink Ka-band allocated to satellite communications (27.5–31 GHz). Good agreement is obtained between the simulated and measured performances. The measured return loss is greater than 12 dB over the entire frequency band and beyond. High scanning performances are achieved over an angular range of ±50° (±14 beamwidths), with maximum scan losses in the order of 3 dB and good pattern stability over the entire band. The proposed solution is particularly suited for next-generation satellite terminals requiring compact broadband antennas with continuous beam-steering capability over a large angular range. [ABSTRACT FROM AUTHOR]

In this article, a new concept to improve the angular stability of linear-to-circular polarizing reflectors is presented. It is first explicitly demonstrated that existing design approaches heavily rely on the adjustment of the design stack-up, namely, the substrate height and relative permittivity, to the desired operating frequency. An approach is then proposed for decoupling the performance from the substrate parameters. The proposed approach provides increased design flexibility, resulting in performance improvement. Insight on the operating principle is provided resorting to equivalent circuit models. Subsequently, the benefits of the angularly stable reflection polarizer are demonstrated by a practical example involving a multiple beam antenna implemented using materials and processes compatible with satellite missions. The antenna exploits an innovative quasi-optical beamformer as primary feed combined with a cylindrical polarizing reflector. Numerical and experimental results from this antenna architecture are presented to confirm the improvements achieved with the proposed concept over existing designs. The close comparison of simulations with measurements that are achieved validates the concept and the design approach. [ABSTRACT FROM AUTHOR]

A novel technique for feeding microstrip antenna arrays is proposed. It consists of a microstrip feed network designed to operate in dual standing and traveling-wave modes and provide uniform excitation to its elements with either mode. It, therefore, produces a uniform aperture distribution, regardless of the array element input impedances. The traveling wave propagates when radiating elements are matched, but resonant standing wave prevails if loads become mismatched. Since the feed network resonance does not alter the array excitation, it can be used in combination with the radiating patch resonance to broaden the impedance bandwidth. The physical reasons for such behaviors are explained and experimental verification are provided. The generalization of the concept to large arrays is also discussed. Index Terms - Microstrip arrays.

In this paper, shaped continuous parallel plate waveguide delay lenses are proposed. The previous configurations introduced by the authors displayed a residual side lobe imbalance, showing the limitations of elliptical delay lens profiles, derived from a starting bifocal constrained lens. Polynomial profiles are proposed here as a way to enhance the scanning performance and the pattern shape. Optimized configurations demonstrate a reduction in the phase aberration levels over a large scanning range ([−30°, 30°]). The associated radiation patterns demonstrate lower and more balanced first side lobe levels (SLLs) ($\cong -18$ dB), as compared to the previous elliptical approach ($\cong -13.2$ dB). A validation has been proposed through the manufacturing and test of a prototype over the down-link Ka-band ([27.5–31] GHz). Excellent radiation performance [half-power beamwidth (HPBW), SLL] has been experimentally obtained over a wide angular range ([−31.5°, 31.5°]), including low scanning loss and high radiation stability over the entire frequency range. High radiation efficiencies are demonstrated with this fully metallic design, particularly suitable for space applications. The mechanical simplicity offered by the concept is also quite attractive for low-cost multi-beam platforms. [ABSTRACT FROM AUTHOR]

This paper presents the spectral Green’s function (GF) to analyze Fabry–Perot antennas to generate circular polarization (CP). The structure consists of a single cavity created between a partially reflective surface and a high impedance surface, fed by a low directive, linearly polarized source. Elements in the antenna are characterized by tensor impedances. It allows conceiving a circularly polarized antenna supporting a single hybrid leaky-wave mode. Residue analysis is used to demonstrate that a single hybrid leaky-wave mode is sufficient to generate CP. The tool is validated by an antenna design matched over a relative bandwidth of 28.5% with an axial ratio lower than 3 dB. [ABSTRACT FROM AUTHOR]

This letter proposes an efficient design process to reduce the cross polarization of linear-to-circular reflection polarizers illuminated by practical feeds. In particular, we propose a two-step process, where first a geometrical optimization of the unit cell is applied along one plane of the reflector, followed by a progressive rotation of the unit cell in the orthogonal plane. An offset flat polarizer comprised of dipole unit cells fed by a standard gain horn has been used to illustrate the process. Significant improvements in cross-polarization discrimination are demonstrated by simulation. Two breadboards have been manufactured, and their response is compared in order to demonstrate the validity of the design process. Good agreement with measurements is observed corroborating the proposed technique. [ABSTRACT FROM AUTHOR]

A general synthesis approach is proposed for reflectarrays using second order Phoenix cells. It relies on an original spherical representation that transforms the optimization domain in a continuous and unbounded space with reduced dimension. This makes the synthesis problem simpler and automatically guarantees smooth variations in the optimized layout. The proposed mapping is combined with an Artificial Neural Network (ANN) based behavioral model of the cell and integrated in a min/max optimization process. Bi-cubic spline expansions are used to decrease the number of variables. As an application, a contoured beam for space communication in the [3.6-4.2] GHz band is considered. The gain improvement compared to an initial Phase Only synthesis (POS) is up to 1.62 dB at the upper frequency. Full-wave simulation of the final array is provided as a validation. [ABSTRACT FROM AUTHOR]

An analytical model based on geometrical optics is proposed to design and analyze continuous parallel plate waveguide (PPW) lens-like antennas. The proposed design is based on a transversal PPW section working as a lens-like beamformer. By simplifying the propagation inside this transversal section, a bifocal constrained lens model is first defined; it provides a relevant starting point to design the proposed beamformer. A refined model based on ray tracing and with an enhanced performance prediction is achieved by accounting the wave propagation inside the transversal cavity. The numerical analysis of phase aberrations and radiation demonstrate the performance of the proposed beamformer. The results of the ray-tracing model are in a very good agreement with the corresponding full-wave model, while providing a significant reduction in the computational effort, making the proposed model more suitable for advanced optimization processes. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This communication introduces a novel periodic reflector which provides linear to circular polarization (CP) conversion in two frequency bands. Significantly, the reflector converts a slant 45° linearly polarized wave into two orthogonal CPs over two separate frequency bands while further the unit cell dimensions are maintained below the critical grating lobe limit of half wavelength. Unlike previous designs providing this performance, which are based on linear dipole elements, miniaturization is here achieved by exploiting resonances in both TE and TM polarized waves. The operating principle of the polarizer is discussed and a parametric study is presented to derive design guidelines. A prototype working in the satellite Ku-band has been designed and tested to validate the proposed design. The proposed polarizer can find applications in multiple-beam satellite antenna systems in order to reduce the number of reflector apertures in a single-feed-per-beam configuration. [ABSTRACT FROM AUTHOR]

A fast and efficient synthesis procedure for a new class of low-profile frequency selective electromagnetic absorbers with well-defined absorption and reflection bands as well as steep selectivity between the two is proposed. One contribution of this work lies with the combined use of nonresonant subwavelength capacitive and inductive arrays, which leads to low-profile polarization-insensitive and angularly stable designs. Another novelty stems from the use of rigorous synthesis techniques that enable efficiently selecting the cutoff frequencies, reflectivity level, and skirt selectivity for an arbitrary order of the absorption response. Significantly, here we investigate for the first time the out-of-band characteristics of flat absorbers and demonstrate designs which, at frequencies lower than the absorption band, present high reflectivity with a flat reflection phase. Beyond traditional applications, such as stealth, the combination of a well-defined absorption band with such out-of-band reflection properties makes the proposed frequency-selective absorbers pertinent for dual-band satellite-communication antenna reflectors with congruent beams in transmit and receive bands, where the ratio of 1:1.5 between the two bands is normally required. [ABSTRACT FROM PUBLISHER]

A novel all-metal graded index Gutman lens is proposed. It exploits an interleaved metasurface unit-cell with glide symmetry that can provide high values of equivalent refractive index with low frequency dispersion. The result is a compact lens with broadband performance and a wide field of view up to ±70 ° . The proposed lens exhibits low loss, directive beams and is an appealing candidate for space applications. The design approach introduced can be applied to other graded index lenses with circular symmetry using rectangular or circular periodic structures.