An ultra-wideband (UWB) absorber designed by equivalent circuit model (ECM) is presented in the paper. The structural parameters of multi-layer absorbers were calculated for full-wave simulation so as to verify the accuracy of this method. The simulation results illustrated that the ideal frequency response can be easily and quickly obtained by using ECM, such as single narrow absorption band, dual-band absorption peak and ultra-wide absorption band. A 20 × 20 quadruple-layer absorber was fabricated and tested, which obtained 10-dB radar cross section reduction (RCSR) from 2.1 GHz to 37.5 GHz with bandwidth ratio (BWR) of 17.62:1. The overall dimensions of the unit cell structure is 280×280×14 mm3 (1.96 λmax × 1.96 λmax × 0.098 λmax), and the absorber exhibits stable response on conformal cylinders with central angles of 30° and 60°. Moreover, in order to reduce the influence of high-order modes above U-band, the space mapping (SM) technique was introduced to optimize the absorber’s parameters, which greatly expanded the high frequency absorption bandwidth. A 10-dB RCSR was achieved from 3 GHz to 94 GHz with BWR of 31.33:1.

An efficient optimizing method of ultra-wideband radar cross-section (RCS) reduction metasurface involve unit amplitude differences and mutual coupling effects is proposed in the letter. Multiple unit phase cancellation was used to broaden RCS-reduction bandwidth. The genetic algorithm was utilized to further design and select the optimal combination from various tiles. To improve the optimization efficiency and accuracy, the space mapping (SM) technique was exploited to refine the design process, which involves the interactions of scattering fields among tiles and subarrays in wideband. Meanwhile, the constraint of wide-angle oblique incidences is also considered in wideband low RCS design. An ultra-wideband RCS reduction checkboard meatsurface can be accomplished by fast optimization of low-cost coarse model and few parameter mapping courses between fine and coarse model. A 10dB RCS reduction for HH and VV polarizations under normal and other oblique incidence angles can be achieved from 5 to 40 GHz. Good agreements between simulation and experiment results are obtained.

A hybrid efficient optimizing method of wide scanning sparse planar array involve mutual coupling is investigated in this letter. The former work of matrix enhancement and matrix pencil (MEMP)-based synthesis method is extended to the design of pattern reconfigurable sparse arrays in wide angle scanning. The genetic algorithm was utilized to further optimize the reconstructed sparse array including the actual antenna element, which differs from the only array factor synthesis of MEMP. To improve the optimization efficiency and design accuracy, the space mapping technique was exploited to accomplish the optimizing design, which also involves the interactions among elements into the optimizing process. A wide scanning sparse array can be realized by the new relationship of parameter mapping courses between low-cost coarse model optimizations and high-accuracy fine model validations based on the characteristic mode and multilevel fast multipole algorithm. Numerical examples show the efficiency of the proposed method.

In the letter, a wideband dual circularly polarized (CP) waveguide antenna array is designed for K and Ka dual-band satellite communications. A multi-stage square waveguide structure is exploited into the radiating part to facilitate the excitation of a dual polarization response. A ridge waveguide polarizer is integrated to form the left-hand circular polarization (LHCP) and the right-hand circular polarization (RHCP). For a better arrangement of the feeding network, a transition structure with E-plane waveguides to double-ridge waveguides reduces the cross-sectional area of the feeding network. An 8 x 8 array antenna prototype was designed, fabricated and measured for demonstration purposes. The axial ratio (AR) and impedance bandwidth of the array antenna are more than 45%, according to simulation and measurement results. Input reflection coefficient and isolation lower than -15 dB for the dual CP from 19 to 30 GHz, the total antenna efficiency for the entire operating band exceeded 72%. For both polarizations, the peak gain ranges between 24.6 and 28.8 dBi from 19 to 30 GHz.

An equivalent fractional order orbital angular momentum (OAM) mode based on concentric uniform circular array (CUCA) is proposed in this paper. It is known that the azimuthal resolution of electromagnetic vortex imaging is closely related to the number of OAM modes. Although the multiple-in-multiple-out (MIMO) scheme gives better azimuthal resolution than the multiple-in-single-out (MISO) scheme, it suffers aliasing problem, which means the scattering points with their azimuthal difference larger than 180 degree can not be separated correctly. One possible way to solve this is adding fractional modes in MIMO scheme, but unfortunately, fractional modes are unstable and can not transmit to far field. In this paper, an equivalent fractional order OAM mode is introduced to deal with the problem to achieve higher azimuthal resolution by MIMO scheme. The transmitted and received modes are set to be two adjacent integer modes to realize an equivalent fractional mode. Since the radiation patterns generated by uniform circular array (UCA) for different modes are not aligned, concentric uniform circular array (CUCA) is applied and optimized to overcome this shortage. Simulation results demonstrate the validity of the proposed method.

An effective uncertainty analytical method based on method of moments (MoM) is proposed for the scattering analysis of 3-D objects with varying shape. The uncertainties of the geometric shape are described by several random variables in the integral equations through the non-uniform rational B-spline (NURBS) surface modeling approach. All random variables are independent. Therefore the scattering properties of the 3-D object with uncertain geometric shape can be quantified by perturbation approach with less cost of computational resource than the standard Monte Carlo (MC) method. Numerical results demonstrate the effectiveness of the proposed method.