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While metamaterial aperture imaging systems do not require mechanical scanning equipment or complex components by employing a spatially variant radiation field, they require large amount of data and many computations. In this paper, we deduce the contribution of the resonator to the radiation fields of the metamaterial aperture. We propose a fast range decoupling algorithm that can improve the data processing speed and obtain real-time images of far-field scenes. The algorithm decomposes the scene into numerous range cells, drastically reduces the range of interest, and reconstructs the scene in parallel. Simulation results show that computational cost is significantly decreased and image quality is maintained.

Combining the search depth of particle swarm optimization (PSO) algorithm and the search breadth of invasive weed optimization (IWO) algorithm, an offline algorithm, based on IWO-PSO for joint correction of gain-phase errors and mutual coupling errors, is proposed. Firstly, a known auxiliary source is used to establish an objective function containing both gain-phase errors and mutual coupling errors, and then the IWO-PSO algorithm is used to search for those array errors satisfying the optimal values of the objective function through an alternating iteration procedure. The proposed method does not need prior knowledge of array perturbations, and has good estimation performance of DOA and array errors. Compared with other calibration methods based on optimization algorithms, the RMSE curve of the proposed method for DOA estimation is closer to CRB curve.

In order to improve the prediction accuracy of the pattern of the reflector antenna with phased array feed, a high-precision semi-physical pattern prediction method based on the combination of the electric field and circuit priori measurement data is proposed in this paper. Combined with the differential evolution algorithm, the proposed method is applied to the beam optimization of the reflector antenna with phased array feed. For a given configuration of the reflector antenna with phased array feed, several examples are optimized efficiently and accurately. The proposed method greatly improves the accuracy of the optimization of the reflector antenna with phased array feed.

A novel online antenna array calibration method is presented in this paper for estimating direction-of-arrival (DOA) in the case of uncorrelated and coherent signals with unknown gain-phase errors. Conventional calibration methods mainly consider incoherent signals for uniform linear arrays with gain-phase errors. The proposed method has better performance not only for uncorrelated signals but also for coherent signals. First, an on-grid sparse technique based on the covariance fitting criteria is reformulated aiming at gain-phase errors to obtain DOA and the corresponding source power, which is robust to coherent sources. Second, the gain-phase errors are estimated in the case of uncorrelated and coherent signals via introducing an exchange matrix as the pre-processing of a covariance matrix and then decomposing the eigenvalues of the covariance matrix. Those parameters estimate values converge to the real values by an alternate iteration process. The proposed method does not require the presence of calibration sources and previous calibration information unlike offline ways. Simulation results verify the effectiveness of the proposed method which outperforms the traditional approaches.

In this paper, three parameters of targets in bistatic multiple-input multiple-output (MIMO) radar are estimated based on sparse signal reconstruction. First, 2D scanning space in bistatic MIMO radar is divided into dense meshes, and a sparse signal model of multiple measurement vectors is constructed. Second, a constrained objective optimization function is established by using traditional $l2$ norm and is converted to an unconstrained objective optimization function. A conjugate gradient method is utilized to solve the inverse operation of a large-scale matrix and to avoid singular problems during sparse iterations. Even in 2D dense meshes of $90\times 90$ , the speed of convergence can be accelerated. The direction of arrival, the direction of departure, and the reflection coefficient of multiple targets in bistatic MIMO radar are estimated, and the 3D parameters of each target automatically match. Simulation results verify the validity and fast convergence of the proposed method.

Phase-only optimization of asymmetric multiple beams reflectarray with single feed is investigated in this paper. The conventional design approaches are first reviewed. Secondly, for design of asymmetric multiple beams reflectarray with arbitrary gain levels and beam directions, a general method based on invasive weed optimization is proposed. Then, practical considerations for applying the proposed method to design multiple beams reflectarray are talked over. For illustrating the effectiveness of the proposed method, several multiple beams design cases with different design requirements are optimized through this method, and the optimized results are analyzed through simulation approach based on array theory. The simulation results show that the optimized cases demonstrate the satisfactory multiple beams performance.

In this paper, the direction of arrival (DOA), the direction of departure (DOD) and the reflection coefficient of multiple targets in bistatic MIMO radar are estimated based on sparse signal restoration. Firstly, a two-dimension scanning space of bistatic MIMO radar is divided into dense grids, and a sparse signal model of multiple test vectors (MMV) is constructed. Secondly, a constrained optimization model with 12 norm is transformed into an unconstrained optimization model with Lagrange multipliers and is solved iteratively. Simulation results show that the three parameters of each target are estimated simultaneously and matched automatically without additional pairing, which verifies the effectiveness of the method.

As the important case of conformal arrays, conformal arrays on cylindrical surfaces have been widely used in radar and communication systems. This paper explores the chances of designing conformal reflectarray on cylindrical platform. An extended array theory method is proposed in this paper for analyzing the radiation patterns of cylindrical conformal reflectarray. The radiation characteristics of conformal reflectarray on convex and concave cylindrical surfaces are studied, and the performances of the two cases are compared with planar cases. It is shown that the cylindrical conformal reflectarray can be a good candidate of high gain antennas for applications where a slightly curved conformal platform is available.

The performance of high-resolution algorithm will degrade badly in the presence of sensor gain and phase errors. To deal with this problem, a new method for array calibration using Invasive Weed Optimization (IWO) algorithm is proposed. The method, starting from basic principle of subspace, combining with IWO algorithm, and then using one signal source, calibrates gain and phase errors of uniform linear array (ULA). The steering vector is modified to get more accurate direction of arrival (DOA). The simulation results show the practicability and validity of the proposed algorithm.

In most scenes of through-the-wall imaging (TWI), the observation zone is spares. So the radar signals could be processed using Compressive Sensing (CS) technique. Existing greedy algorithms for CS, such as orthogonal Matching Pursuit (OMP) algorithm and Compressive Sampling Matching pursuit (CoSaMP), suffer from artifacts and low resolution respectively. To cover the shortage of existing algorithms, a modified Compressive Sampling Matching Pursuit algorithm is proposed. By using the orthogonality among selected basis-signals and backtracking strategy for basis-signals reevaluation, the proposed algorithm could reconstruct radar signal. Then the image of observation zone could be got using Delay and Sum (DAS) beamforming method. Measurement results demonstrate the effectiveness of the proposed algorithm.

A novel scheme is introduced to design the high gain beam scanning reflectarray antennas for limited scan range application. At first, various existing schemes for beam scanning reflectarray antennas design are reviewed and it is concluded that as a convenient design scheme, the feed displacement technique is preferred for limited scan range applications. In order to improve the scan range, a bifocal single reflector aperture phase is introduced for reflectarray aperture phase design, and in order to further improve the performance, a circular path for feed displacement is introduced to take the place of the conventional lateral path. Based on the introduced scheme, a Ku band bifocal single reflectarray antenna is designed for limited scan range application. The scan performances of the designed reflectarray are analyzed numerically and compared with conventional parabolic design. Numerical results show that the bifocal design shows significant improved scan performance with less 0.8 dB gain loss and lower than -13 dB side lobe level over entire scan range -30° to +30°, which illustrates that the bifocal design for limited field of view beam scanning reflectarray is a promising attempt.