The analysis of the target's broadband electromagnetic scattering characteristics plays an important role in radar stealth and recognition areas. The traditional method of moments (MoM) needs to calculate the currents at each frequency point when analyzing the target. With the increase of the target electrical size and complexity, the radar cross section (RCS) of the target changes drastically with frequency, it is necessary to calculate the accurate frequency response with a small frequency interval, which is very time-consuming in calculation and not feasible. This paper proposes to combine the subdomain method of moments (SMoM) with the Chebyshev approximation technique (CAT) to efficiently analyze the electromagnetic scattering of arbitrary shaped objects over a broad frequency band. In the SMoM technique, the whole object can be divided into several regions, each of which can be independently solved by the method of moments (MoM). The CAT technique is employed to expand the unknown current coefficients into a Chebyshev series for achieving fast frequency sweeping. Instead of direct point-by-point simulations, it is only necessary to calculate the currents by SMoM at several Chebyshev-Gauss frequency sample points. Furthermore, the Chebyshev series are matched via the Maehly approximation to a rational function to improve the accuracy. Numerical examples show that the hybrid technique can greatly reduce the computation time without loss of accuracy.
© 2013 IEEE.

A microstrip-fed slot antenna with dual rejection bands is designed and prototyped for ultrawideband (UWB) applications. The rejection band for WiMAX is achieved by symmetrical etching a pair of nested four-Arm spiral slots on the ground plane. Selfinterdigital electromagnetic band-gap (EBG) structures are embedded to create other rejection bands for WLAN and are placed on both sides of the gradient T-shaped microstrip-fed. The simulated result and measurement data show that the antenna impedance bandwidth (Voltage Standing Wave Ratio is less than 2) covers the entire UWB bandwidth range with two eliminated bands of 3.22-3.81 GHz (0.59 GHz, 16.7%) and 5.11- 5.84 GHz (0.73 GHz, 13.4%). In addition, the designed antenna achieves a stable gain and exhibits omnidirectional radiation patterns except at rejection frequency bands, which makes it a suitable candidate for UWB applications that will not be interfered by WiMAX/WLAN systems.
© ACES.

A microstrip-fed slot antenna with dual rejection bands is designed and prototyped for ultra-wideband (UWB) applications. The rejection band for WiMAX is achieved by symmetrical etching a pair of nested four-arm spiral slots on the ground plane. Selfinterdigital electromagnetic band-gap (EBG) structures are embedded to create other rejection bands for WLAN and are placed on both sides of the gradient T-shaped microstrip-fed. The simulated result and measurement data show that the antenna impedance bandwidth (Voltage Standing Wave Ratio is less than 2) covers the entire UWB bandwidth range with two eliminated bands of 3.22-3.81 GHz (0.59 GHz, 16.7%) and 5.11-5.84 GHz (0.73 GHz, 13.4%). In addition, the designed antenna achieves a stable gain and exhibits omnidirectional radiation patterns except at rejection frequency bands, which makes it a suitable candidate for UWB applications that will not be interfered by WiMAX/WLAN systems.

Experimental results reported in many literature have demonstrated that an antenna array should have two or more grating lobes in its scattering pattern; however, it is not clear how these grating lobes occur and vary. In this paper, we propose a new method to predict the number and location of scattering grating lobes generated by an array antenna. In the proposed method, the radar cross section (RCS) of array antenna can be decomposed into multiplication of the array RCS factor and the element RCS factor. The array RCS factor bears universal applicability so that it can be used to directly determine scattering properties of array antenna. Compared with the full-wave simulation techniques, the new method requires much less computation time and memory storage so that it is more suitable to be employed as the basis of a synthesis method to predict the desired RCS pattern of a large array antenna. As examples, the scattering properties of the dipole antenna arrays are investigated to validate the new method, numerical results demonstrate that the number and location of scattering grating lobes predicted by using the proposed method coincide with those simulated by using a MoM based commercial; software FEKO.
© ACES.

The PMCHWT-IE-FFT-BURA is applied to the wideband analysis of electromagnetic scattering property of homogeneous targets. Over the broad frequency band, the fast computation is achieved by the Maehly expansion on the basis of the Chebyshev approximation of the electric and magnetic currents. On the Chebyshev sampling points, PMCHWT-IE-FFT greatly reduces the memory requirement by sparsely storing the impedance matrix and decreases the computational time to the greatest degree by block acceleration of the matrix-vector product. Finally, numerical results show that the proposed method can make efficient analysis of wideband property of homogeneous targets without sacrificing accuracy much .
© 2016, Progress In Electromagnetics Research. All rights reserved.

A novel method is proposed through an effective combination of the subdomain adaptive integral method (SAIM) with the fast far-field approximation (FAFFA) for efficient computation of electromagnetic scattering problems. In the SAIM technique, the whole perfectly electrically conducting structure is decomposed into subdomains and each subdomain is properly handled by the AIM with its local Cartesian grid individually. A current continuity boundary condition is introduced on the interface between contiguous subdomains to guarantee the accuracy. Moreover, the FAFFA technique is utilized to speed up the process of updating the modified excitation vectors. Numerical results show that the present hybrid method can not only significantly decrease the number of auxiliary grid points and the memory requirement of Green's function matrix, but also improve the convergence of the iterative process compared to the conventional AIM.
© 2016 IEEE.

The asymptotic waveform evaluation (AWE) technique is utilized to deal with broadband electromagnetic problems of surface-wire junction geometries in this paper. To ensure the current continuity, triangles-to-segments junction model is used and the Rao-Wilton-Glisson (RWG) and triangular basis functions are used to solve the distributions of current on perfect electric conductor and wire, respectively. Then, the current on surface conductor, wire, and junctions are expanded in a rational function via Padé approximation. The AWE technique needs to store the high-order derivatives of the self-impedance and mutual-impedance matrices of surface-wire, which increase the memory requirements. Thus, the adaptive integral method is employed to reduce memory requirements and to accelerate the matrix-vector multiplications in an iterative solver. Finally, some numerical examples are shown to demonstrate the efficiency and accuracy of the proposed method.
© 2015 Taylor & Francis.