number of right-hand sides to be solved for the complete monostatic RCS calculation is 91 for each example. It can be seen that the number of MVPs of the SAI-GMRES method varies largely with respect to incident angles (i.e., right-hand sides), while that of the GMRESE methods are more similar and almost constant for each example. This is another advantage of the GMRESE method proposed in this article. More detailed comparisons can be found in Table 5, in which the cumulated number of matrix-vector products and the total elapsed solution time for a complete monostatic RCS calculation are summarized using both the SAI-GMRES method and the GMRESE methods. In this table, it can be observed that the overall gain ranges from a factor of 3.5 to 5.9 when compared in terms of CPU time. CONCLUSIONS AND COMMENTSIn this article, we have described an enhanced GMRES method combined with MLFMA for solving linear systems from electromagnetic wave scattering problems. We explicitly compute and save the approximate eigenvectors associated with the eigenvalues close to the origin, either by the ARPACK software in a preprocessing phase or by the GMRES-DR method as a byproduct during the iteration process. The spectral information is then augmented into the Krylov subspace of the GMRES method to recover global information in the MLFMA context. Numerical experiments of typical examples are performed and comparison is made with the SAI preconditioned GMRES method, which shows the GMRESE method proposed in this article is more efficient and can reduce significantly both the iteration number and the overall simulation time.The novelty of this approach presented in this article compared to the augmentation techniques in Ref. 9 is that the proposed method induces a global deflation in the spectrum of the preconditioned matrix. The combined effect of the preconditioning techniques that cluster most of the eigenvalues to one, coupled with the augmentation technique that shifts the rest of the smallest eigenvalues of the spectrum can be very beneficial for the convergence of the Krylov iterative methods. Moreover, the price of augmenting eigenvectors into the Krylov subspace in the classical augmented GMRES method, that is the k additional matrix vector products, is avoided, since the spectral information is explicitly saved and applied at every cycle. Recently, radio frequency identification (RFID) in the UHF band has gained popularity in many applications, because it provides a long reading distance, fast reading speed, and large information storage capability. In RFID systems, tags are usually attached to objects having various material properties. Among them, metallic objects strongly affect the performance of a tag antenna including radiation efficiency and gain levels. To overcome these problems, planar inverted-F and microstrip patch antennas have been proposed for RFID tag applications. However, these antennas have a narrow bandwidth and thick height, and the resonant frequency can easily be shifted depending on the characteristics o...

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In this article, a dual-band multiple input multiple output (MIMO) antenna is proposed for Mobile WiMAX applications. The designed MIMO antenna consists of two planar inverted F antennas (PIFAs) and two isolators. The PIFAs have a volume of 12 Â 10 Â 4 mm 3 , which is small enough to be incorporated in a mobile MIMO terminal. The two isolators are designed symmetrically and placed between the two PIFAs to enhance the isolation performance of the MIMO antenna by suppressing the current flow between the antennas in the 2.3 and 3.4 GHz bands. The measured isolation values (S 21 ) are lower than À15 and À22 dB at the 2.3 and 3.4 GHz bands, respectively. The key design parameters are extracted, and the parametric analysis performed. Also, the overall performance of the optimized MIMO antenna is presented.

SUMMARYThis paper proposes a microstrip patch antenna for 2.45 GHz Industrial Scientific Medical (ISM) band Wireless Body Area Network (WBAN) applications. To enhance the front-to-back ratio (F/B) and specific absorption rate (SAR), an electrically coupled LC resonator is introduced. The overall dimensions of the proposed antenna are 54 mm × 45 mm × 2.4 mm and it has a gain of over 1 dBi for the entire 2.45 GHz ISM band. The proposed antenna has an enhanced F/B ratio and specific absorption rate, compared with those of a conventional patch antenna. key words: wireless body area network (WBAN), patch antenna, electrically coupled LC resonator (ELC)

In this article, a compact tag antenna for UHF RFID systems is proposed. The proposed antenna consists of a T-matching network, meandered dipole, and an inverted-U shaped parasitic element. The tag antenna is miniaturized by utilizing inductive coupling between the meandered dipole and the parasitic element. The overall dimension of the proposed tag antenna is 17.96 Â 35.6 mm 2 . It has a gain of 1.52 dBi and a maximum reading distance of 6.3 m at 915 MHz. The size of the tag antenna is about 33% of that of other RFID tag antennas, such as a meander line antenna and a coplanar inverted-F antenna. In spite of its small size, the proposed tag antenna yields superior performance.