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A new design method for ultrabroadband radar cross section (RCS) reduction by exploiting characteristic complementary polarization conversion metasurfaces (PCMs) is proposed and validated. The proposed method lifts the conventional bandwidth limitation enforced by the performance of a single PCM and expands the RCS reduction bandwidth. A systematic strategy for ultrabroadband RCS reduction design is developed and an effective reflection coefficient amplitude of the composite surface ($\Gamma _{ {eff}}$) is derived as a new RCS reduction indicator. Based on this indicator, complete polarization conversion (CPC) frequency points of PCM are identified as important characteristics, and PCM pairs with interleaved CPC points, termed as initial PCM (I-PCM) and complementary PCM (C-PCM), are designed to compensate each other for ultrabroadband RCS reduction. A scaling-and-tuning two-step method for designing the C-PCM of a specific I-PCM is developed and validated. To further improve RCS reduction performance, taking the ${\Gamma _{ {eff}}}$ as an indicator, the particle swarm optimization (PSO) algorithm is used to select the optimal I-PCMs, C-PCMs, and their area ratios. Finally, an ultrabroadband RCS reduction surface is designed, fabricated, measured, and validated. It realizes 10-dB monostatic RCS reduction ranging from 7.6 to 26.2 GHz (110.7% relative bandwidth) which exceeds the polarization conversion bandwidth of each individual PCM. Besides, good polarization insensitivity and bistatic RCS reduction performance are also obtained. The proposed method provides a new route for designing broadband RCS reduction surface based on PCMs with unsatisfactory characteristics and greatly alleviates the performance requirement for PCMs. [ABSTRACT FROM AUTHOR]

In this article, a 2-D bistatic attributed scattering center (BASC) model is developed to represent the bistatic return from a perfect electric conducting (PEC) target, based on the derived analytic scattering solutions of seven canonical primitives. Because of its unified and concise form, the BASC model is useful for extracting the geometrical features of targets from synthetic aperture radar (SAR) echoes. However, estimating the parameters of the BASC model is an ill-posed inverse problem. To reduce the ill-posedness, we present a sparse method for bistatic inverse scattering that incorporates differential evolution (DE) into doubly orthogonal matching pursuit (DOMP). The experimental results not only verify the validity of the parameter inversion method but also demonstrate the applicability of the proposed model. [ABSTRACT FROM AUTHOR]

Based on geometrical optics (GO), this paper develops a representation theory of multiple specular reflections from perfect electric conducting target with an arbitrary patchwise smooth surface. In the course of rays’ multiple reflections, the polarization of each ray is found to change in a manner consistent with the variations of its propagating direction, which can be described with an equivalent 3-D rotation transformation. This transformation provides a new representation of the polarization rotation effect induced by multiple reflections. More importantly, the parameters of this transformation characterize the target’s GO field response, and their values can classify six classes of geometrical structures. Furthermore, we derive explicit formulas relating these parameters to target’s geometrical attributes for double and triple reflections, by using a quaternion algebra method. In order to validate this representation theory, we construct a parametric model of bistatic scattering from an arbitrary multiplate structure, by combining the GO–physical optics (PO) method with this representation. Through two special cases, the representation theory is validated by comparing the RCSs calculated by the parametric model with those by a shooting and bouncing ray (SBR) algorithm. The representation and derived concise parametric model are useful for extracting geometrically relevant features from bistatic radar measurement. [ABSTRACT FROM AUTHOR]

A theoretical foundation of wave propagation modeling for tunnels in complex meteorological environments is presented by using the parabolic equation (PE) method. The finite differential scheme is applied to solve the PE; thus, the calculation can be taken in each 2-D transverse plane. As a result, the computational efficiency can be enhanced greatly. Moreover, the effective permittivity of the meteorological environment is given and then the propagation attenuation in the meteorological environment can be estimated. In this way, the wave propagation of tunnels in the complex meteorological environment can be modeled by updating the refractive index for PE. Finally, the vehicles in the tunnels for diverse meteorological environments are also considered in the numerical results. [ABSTRACT FROM AUTHOR]

This communication presents a dual-port reconfigurable square patch antenna with polarization diversity for 2.4 GHz. By controlling the states of four p-i-n diodes on the patch, the polarization of the proposed antenna can be switched among linear polarization (LP), left- or right-hand circular polarization (CP) at each port. The air substrate and aperture-coupled feed structure are employed to simplify the bias circuit of p-i-n diodes. With high isolation and low cross-polarization level in LP modes, both ports can work simultaneously as a dual linearly polarized antenna for polarimetric radars. Different CP waves are obtained at each port, which are suitable for addressing challenges ranging from mobility, adverse weather conditions and non-line-of-sight applications. The antenna has advantages of simple biasing network, easy fabrication and adjustment, which can be widely applied in polarization diversity applications. [ABSTRACT FROM PUBLISHER]

Plane wave scattering by an infinite, three-dimensional wedge whose faces are characterized by periodic anisotropic impedances is investigated. An improved hybrid of the moment method (MM) and the physical optics (PO) is proposed to calculate the equivalent electric current on the wedge surface. As for the infinite periodic wedge surface, a periodic representation of the scattering surface is used to prevent nonphysical edge effects in the scattering evaluation. The surface of the wedge is split into an MM region and a PO region. In the implementation of MM, the evaluation of the interaction matrix elements in the MM region is simplified by deriving six universal series. Moreover, the PO-current is modified by a diffracted current to improve its accuracy. The accuracy and effectiveness of the proposed approach is validated and demonstrated by using series solution, the method in [T. B. A. Senior, “Solution of a class of impedance wedge problem for skew incident,” Radio Sci., vol. 21, no. 2, pp. 185–191, 1986], and the two-dimensional improved MM-PO approach under several canonical two-dimensional wedge cases. At last, the proposed approach is applied to analyze the scattering from the wedges with periodic anisotropic impedance faces, and the numerical results are presented. [ABSTRACT FROM PUBLISHER]

This paper presents a novel and original approach for the evaluation of electromagnetic (EM) scattering from electrically large and complex target coated with uniaxial electric anisotropic medium (UEAM) layer. The evaluation includes two indispensable aspects, the geometry modeling of the target and the determination of the surface currents. Once the equivalent surface currents (ESCs) induced on the outer surface of the coated target are determined, the scattered field could be calculated by the corresponding radiation integrals. First, the outer surface of the arbitrarily shaped target is discretized using flat triangle facets. Second, the ESCs on any facet are deduced from the surface fields, which involve a complicated coupling of type I and type II waves existing in the UEAM. Thus, the determination of the surface fields and the ESCs on the surface of the target with large radius of curvature is the crux of the whole evaluation. By making the tangent plane approximation, used in the physical optics (PO) method, any discretized flat facet could be approximated as an infinite PEC plate coated with a homogenous UEAM layer. Thereafter, the scattering from the infinite coated plate is asymptotically calculated by using the proposed spectral domain method combined with saddle point evaluation (SDM-SPE). Ultimately, comparisons of the proposed asymptotic solution with the reference solutions calculated numerically confirm the validity and efficiency of the proposed SDM-SPE. Numerical results of several canonical and complex targets coated with UEAM layer are given by the proposed approach for the first time. [ABSTRACT FROM PUBLISHER]

Adopting a method of moments/physical optics (MoM-PO) hybrid method, this communication explores the electromagnetic scattering from three-dimensional (3-D) isotropic or anisotropic impedance surface, based on an impedance boundary condition (IBC). According to the surface equivalence principle, the electromagnetic scattering can be replaced by the radiation of surface electromagnetic currents in a MoM- and a PO-region, with the currents expanded in Rao-Wilton-Glisson (RWG) vector basis functions. The simulation of impedance surface is performed with the electromagnetic parameters characterized by a surface impedance dyadic. The hybrid method allows for a substantial reduction of computation time and memory requirement, while the numerical results agree well with the exact solutions such as Mie series, which proves the validity of the proposed method. [ABSTRACT FROM PUBLISHER]