Shuai Zhang

A NOVEL IGA-EDSPSO HYBRID ALGORITHM FOR THE SYNTHESIS OF SPARSE ARRAYS

Based on the improvements of both Genetic Algorithm and Particle Swarm Optimization, a novel IGA-edsPSO(Improved Genetic Algorithm-extremum disturbed simple Particle Swarm Optimization) Hybrid algorithm is proposed in this paper. An improved performance of GA is achieved by reducing the array space. By discarding the particle velocity vector in the PSO evolutionary equation, the sPSO (simple PSO) can avoid the problem of slow later convergence velocity and low precision caused by determining the maximal velocity vector factitiously. And the edsPSO can overstep local extremum point more effectively with the help of the extremum disturbed factor. The proposed IGA-edsPSO Hybrid algorithm is used in the design of the sparse arrays with minimum element spacing constraint. Given the array aperture and the number of the array elements, the suppression of the peak sidelobe level (PSLL) with a certain half power beamwidth (HPBW) restriction is implemented with a high efficiency by optimizing the HPBW and PSLL synchronously. The simulation results show that faster convergence velocity (which means less computation time) and lower sidelobe level are obtained using IGA-edsPSO compared to IGA, standard PSO, GA-PSO and GA-sPSO.

A Modified PSO for Low Sidelobe Concentric Ring Arrays Synthesis with Multiple Constraints

This paper describes a modified particle swarm optimization (MPSO) for the synthesis of the low sidelobe concentric ring arrays. The MPSO has been utilized to optimize the element placement in a concentric ring array to obtain the lowest peak sidelobe level (PSLL). And here the multiple optimization constraints include the array aperture, the minimum ring spacing and the element spacing in each ring. Unlike standard PSO using fixed corresponding relationship between the optimal variables and their coding, the MPSO utilized the coding resetting of optimal variables to avoid infeasible solution during the optimization process. Also, the proposed approach has reduced the size of the searching area of the PSO by means of indirect description of individual. The simulated results confirming the great efficiency and robustness of this algorithm are provided in this paper.

Optimum Spatial Arrangement of Array Elements for Suppression of Grating-Lobes of Radar Cross Section

A new method to optimize the radar cross section (RCS) for array antennas is presented. A previous work has reported that the RCS of an array is the product of the array RCS factor multiplying the element RCS factor. In this method, the strong scattering from an equally spaced array can be considerably reduced at some certain directions by optimizing the array RCS factor. With the proposed method, the optimized array will scatter waves at a much lower level against prescribed incident directions. In order to illustrate the validation of the proposed method, a planar dipole array and a linear array with bowtie antenna elements are designed and optimized by the proposed method. The numerical and simulated results show that the RCS pattern of equally spaced array generally has some grating-lobes at some certain directions. Hence, the proposed method is applied to suppress these grating-lobes to design a low RCS array. The algorithmically optimized and simulated results validate that the proposed method can help to suppress these grating-lobes.

A NEW METHOD FOR DETERMINING THE SCATTERING OF LINEAR POLARIZED ELEMENT ARRAYS

A new method for analyzing the RCS of array antennas is presented in this paper. In the proposed method, the total RCS of the array can be simply decomposed to array RCS factor and element RCS factor. By this decomposition, the effects of the array distribution and antenna elements on scattering can be clearly exhibited. Thus, the analyzing of scattering characteristic of array antennas becomes easier. Moreover, proposed method has good compatibility for calculating the RCS of the array antennas with the same array distribution for different element.

A New Approach for Synthesizing Both the Radiation and Scattering Patterns of Linear Dipole Antenna Array

A new approach for simultaneously synthesizing the radiation and scattering patterns of linear dipole antenna array is investigated. In this method, the analytical formulas of the radiation field and scattered field of linear dipole antenna array are derived in terms of self-impedance, mutual-impedance and terminal load impedance. So the mutual coupling effects between the elements can be taken into account. Based on these two formulas, the desired radiation and scattering patterns of the array can be synthesized simultaneously by optimizing element placement. As an example, the proposed method is used in designing a linear dipole antenna array with low radiation and scattered sidelobe level. Numerical results validating the accuracy and great effectiveness of the method are also provided in this paper.

A Novel Time-Domain Physical Optics for Computation of Electromagnetic Scattering of Homogeneous Dielectric Objects

A novel time-domain physical optics (TDPO) is proposed to determine the transient response of electromagnetic scattering of electrically large homogeneous dielectric targets modeled with triangular facets. Formula of the novel TDPO is derived, in which a time-domain convolution product between the incident plane wave and the time-domain physical-optics (PO) integral is included. The time-domain PO integral is evaluated with a closed-form expression based on a Radon transform interpretation, which makes the novel TDPO highly e-cient in speed. The wideband radar cross section (RCS) is conveniently obtained from the transient response with a fast Fourier transform (FFT). Numerical results demonstrate the e-cacy of the new method.

Application of the Active Element Pattern Method for Calculation of the Scattering Pattern of Large Finite Arrays

This letter extends the concept of the active element pattern method that is used to solve the array radiation problem when scattered fields of large finite arrays are calculated. We name this method the original induced element pattern method (OIEPM). The theoretical derivation of the method is presented. In addition, to overcome the limitation and simplify the operation of the OIEPM, an improved induced element pattern method (IIEPM) is proposed, which transforms the large array calculation problem into two small array problems. Unlike the OIEPM that requires calculation of the induced element pattern (IEP) of all the elements of the subarray, the IIEPM merely needs to calculate the fully scattered field of two small arrays. Meanwhile, the effects of the mutual coupling between elements and the edge diffraction are rigorously taken into account. Compared to other numerical and active (or induced) element pattern methods, the IIEPM can greatly reduce the computational cost and simplify the operational procedure. Examples of microstrip patch antenna arrays are analyzed to assess the accuracy and generality of the IIEPM. Numerical examples show that the scattering patterns calculated by the IIEPM and those simulated by the HFSS are in good agreement.

Analysis and Synthesis of Radar Cross Section of Array Antennas

Our previous work has proved that the Monostatic Radar Cross Section (MRCS) of array antennas can be decomposed into the multiplication of array MRCS factor and element MRCS factor. The principle was derived in a special case that the array only had dipole antenna elements. However, many array antennas have more general antenna elements whose current is aperture distributed along the antenna structure. Obviously it encounters limited application problem when the principle is used to analyze more general array antennas other than dipole arrays. Therefore, the principle is extended into the more general array with arbitrary aperture antenna elements in this paper. In deriving the principle, the devices in the feed are assumed to have identical transmission and re∞ection coe-cients. In order to validate the principle the scattering pattern of a waveguide slot array and an array with helix antenna elements are synthesized utilizing the array RCS factor. The simulation and calculation results prove that the principle is correct for the RCS pattern synthesis of general arrays with aperture antenna elements.

Radiation Pattern of Large Planar Arrays Using Four Small Subarrays

The active element pattern (AEP) method is usually employed to efficiently predict the radiation from large arrays when the direct analysis methods are infeasible. However, the standard AEP method needs to compute and store the AEP of each subarray element, and then the AEPs are used to construct those of the large array. To eliminate this cumbersome process, a simplified AEP method is proposed, which only uses the total radiation field of four small subarrays to construct the radiation pattern of large planar arrays. Theoretical derivation of the proposed method is presented. This method has the same accuracy as the standard AEP method, and it is only effective for broadside and uniform excitation arrays. Example arrays of microstrip patch antennas are analyzed and the calculated patterns agree well with those simulated by HFSS.

A Radon Transform Interpretation of Contour Integral in Time-Domain Equivalent Edge Currents

Time-domain equivalent edge currents (TD-EEC) require the calculation of an integral of the input pulse over the edge contour and thereby yield finite results at the caustics of diffracted rays. Generally, the edge contour is subdivided into a series of straight segments, and the contour integral is evaluated as a sum of the integration over each segment. However, the length of each straight segment should be small enough in order to satisfy the accuracy of integration. In this letter, this integration is interpreted as a Radon transform, on the basis of which an exact closed-form expression is obtained. The accuracy of the derived closed-form expression is not dependent on the length of the integration line of interest. Hence, the need for subdivision can be eliminated for any straight diffracting edge. Some numerical examples are provided to demonstrate the validity and applicability of the proposed approach .