In order to extend the performance of radar absorbing materials, it is necessary to design new structures with wideband properties and large angles of incidence which are also as thin as possible. The objective of this work, realized within the framework of the SAFAS project (self-complementary surface with low signature) is, then, the development of an ultra-wideband microwave absorber of low thickness. The design of such material requires a multilayered structure composed with dielectric layers, metasurfaces, and wide-angle impedance matching layers. This solution has been realized with on-the-shelf materials, and measured to validate the concept. At normal incidence, the bandwidth ratio, defined for a magnitude of the reflection coefficient below −10 dB, is 4.7:1 for an absorber with a total thickness of 11.5 mm, which corresponds to λ/7 at the lowest operating frequency. For an incidence of 60°, this bandwidth ratio is reduced to 3.8:1, but the device remains ultra-wideband.

In this paper, a wideband dual polarized self-complementary connected array antenna with low radar cross section (RCS) under normal and oblique incidence is presented. First, an analytical model of the multilayer structure is proposed in order to obtain a fast and reliable predimensioning tool providing an optimized design of the infinite array. The accuracy of this model is demonstrated thanks to comparative simulations with a full wave analysis software. RCS reduction compared to a perfectly conducting flat plate of at least 10 dB has been obtained over an ultrawide bandwidth of nearly 7:1 at normal incidence and 5:1 (3.8 to 19 GHz) at 60° in both polarizations. These performances are confirmed by finite element tearing and interconnecting computations of finite arrays of different sizes. Finally, the realization of a 28 × 28 cell prototype and measurement results are detailed.

An original method is proposed which associates rigorous 3D finite element methods (FEM) with Floquet modes through FACTOPO multidomain formalism for computing the radar cross section (RCS) of large array antennas. The most original aspect of the method is the fact that the source unit cell is characterized by a generalized scattering matrix (GSM) which does not depend on the plane wave incidence impinging the structure. Consequently, the factorization step of the FEM matrix, which is the main computational effort, is performed only once. The assembling procedure consists then in expressing the FEM GSM matrix in the Floquet mode basis for each incidence and to solve a linear system giving the complex amplitude of the Floquet modes on the array/cell interface. Associated with this formalism, lateral and back structure effects can be treated using physical optics (PO) combined with the equivalent current method (ECM) to improve the accuracy for far broadside incidence.

This paper presents a novel approach for linear to circular polarization (LP-CP) conversion in transmitarray antennas. The proposed conversion mechanism differs significantly from previous published realizations. The concept utilizes a transmission line modeling-based excitation technique, in which a centralized via excitation is split into two striplines carefully designed to balance excitations and guarantee a phase quadrature. The striplines are embedded at the center of the patch antenna allowing a compact footprint and a simple design structure. The applied true-time delay (TTD) technique assures the radiation of a wideband and low axial ratio circularly polarized (CP) field. To optimize bandwidth and transmission efficiency, a stacked patch configuration is also employed, allowing for simultaneous high polarization conversion and transmission efficiency. The unit-cell design methodology is detailed, and two transmitarray designs are realized in both X and Ka bands. Experimental results from a fabricated X-band 20×20 cell array prototype demonstrate a peak aperture efficiency of 30%, accompanied by a simultaneous 16% -1 dB gain and 1 dB axial ratio bandwidths. Furthermore, the measured wideband and highly efficient Ka-band transmitarray with a 70×70 cell array confirmed a remarkable gain of 39.8 dB and 55% aperture efficiency at 29 GHz, surpassing previous LP-CP transmitarray antennas, while maintaining axial ratio values below 1 dB in a bandwidth larger than 26%.

Transmit-arrays (TAs) are a popular cost-effective solution for high-gain antennas at millimeter waves (mmW). The design of these antennas relies on the fine tuning of the sub-wavelength unit-cells that compose the aperture. The TA is illuminated by a source placed at its focal point, forming a very large computational volume in terms of wavelength. The intricacy of the unit-cells increases as new features are implemented, such as dual-band operation and wide angle beam steering, making this antenna even more computationally challenging. Fast and accurate evaluations are required to perform several optimization cycles. In this work, a 25 dBi gain multi-scale Ka dual-band TA for beam-steering applications is analyzed using a massively parallel implementation of the Finite Element Tearing and Interconnecting method, with a two Lagrange Multiplier (FETI-2LM) technique, in the FACTOPO code.

This paper proposes the application of the Finite Element Tearing and Interconnecting method (FETI-2LM) a Domain Decompositon Method (DDM) for the full-wave simulation of large antenna array (few thousands of radiating elements). The proposed methodology makes it possible to efficiently calculate in a post-processing step the antenna patterns for steering directions within the desired field of view while taking into account the active reflection coefficients. The methodology is based on an efficient extraction of the embedded radiating elements far field radiation patterns as well as the Generalized Scattering Matrix (GSM) of the array by implementing massively parallel computers. The beauty of the GSM is its capability to handle the active S-parameters independently of the steering direction. This permits to generate the angulardependent active reflection coefficients by post-processing. This implementation is a step forward to provide us with a tool that permits to evaluate by simulation large antenna array while taking into account all the phenomena and interactions that may degrade the key performances that are required at a higher level, to specify a global system before fabrication.