The specific problems encountered in the design of near-field focused planar microstrip arrays for RFID (Radio Frequency IDentification) readers are described. In particular, the paper analyzes the case of a prototype operating at 2.4 GHz, which has been designed and characterized. Improvements with respect to conventional far-field focused arrays (equal phase arrays) are discussed and quantified.

The forward‐backward method has been shown to be an effective iterative technique for the computation of scattering from one‐dimensional rough surfaces, often converging rapidly even for very large surface heights. However, previous studies with this method have computed interactions between widely separated points on the surface exactly, resulting in anO(N²) computational algorithm that becomes intractable for large rough surface sizes, as are required when low grazing incidence angles are approached. An acceleration algorithm for more rapidly computing interactions between widely separated points in the forward‐backward method is proposed in this paper and results in an O(N) algorithm with increasing surface size. The approach is based on a spectral domain representation of source currents and the Green's function and is developed for both perfectly conducting and impedance boundary surfaces. The method is applied in a Monte Carlo study of low grazing incidence backscattering from very rough (up to 10 m/s wind speed) ocean‐like surfaces at 14 GHz and is found to require only a small fraction of the CPU time required by other competing methods; such as the banded matrix iterative approach/canonical grid and fast multipole methods.

The design of a reflectarray antenna is presented when the radiated field is focused in the near-zone of the array aperture. In particular, the reflectarray antenna is implemented for RFID reader applications at 2.4 GHz. Numerical investigations on the radiation characteristics of this reflectarray, as well as an experimental validation, are presented to demonstrate its feasibility.

F-BM/NSA (3) with computational complexity of is very efficient in method of moment (MoM) modeling of large-scale scat- tering problems from rough surfaces. The previous formulation for PEC surfaces is here extended to treat impedance surfaces. Similarly, numer- ical experiment shows F-BM/NSA is far more efficient than the competitive BMIA/CAG (4) in the order of magnitude. Index Terms—Forward-backward method, method of moment (MoM), rough surfaces, scattering. I. INTRODUCTION Iterative forward-backward method (F-BM) (1), (2) with novel spec- tral acceleration (F-BM/NSA) (3) has been shown to be very efficient in solving the method of moment (MoM) matrix equations for the large-scale scattering problems from the one-dimensional (1-D) rough surface. F-BM requires only three or four iterations to obtain a very accurate solution in many cases of practical applications, and the NSA algorithm reduces the computational complexity from in the original F-BM approach to , where is the number of unknowns in MoM modeling. This is true in the operational count of both the matrix-vector multiplication and memory storage as the surface length increases for a fixed frequency. In the previous paper (3), the algo- rithm was formulated for perfectly electrical conducting (PEC) rough surfaces. The formulations of an NSA algorithm for impedance rough surfaces are presented in this paper. The numerical results will be com- pared with a competitive method of the banded-matrix iterative ap- proach/canonical grid (BMIA/CAG) (4). Similar to the PEC cases, it is found that the CPU time required is also a very small portion of that obtained from BMIA/CAG.

This paper presents the implementation of Luneburg lens antenna based on a 2-D parallel-plate structure for broadband multibeam radiation at millimeter-wave frequencies. In particular, each beam pattern of this 2-D Luneburg lens antenna has a narrow beamwidth along the multibeam dimension, and exhibits a broad beamwidth along the other cross section, analogous to the radiation from a 1-D array of antennas embedded inside the parallel-plate structure. Furthermore, the isolation to external structures by the top and bottom metal parallel plates may reduce the beam distortion from external interferences, and therefore enhance its compatibility to integrate with other radio frequency (RF) components to form an RF subsystem module. In addition, a theoretic model to realize the dielectric variation of Luneburg lens is developed by using stacked multiple planar layered dielectric materials for a cheap manufacture. In this paper, numerical simulation to validate the developed model of 2-D Luneburg lens design is first presented. Afterward, simulation and experimental measurement results of a practical design are both presented to validate the design concept.