Bao Lu

A Microstrip Printed Dipole Antenna with UC-EBG Ground for RCS Reduction

In this paper, A S-band microstrip printed dipole antenna with a distorted uniplanar compact-EBG (DUC-EBG) ground plane is proposed and investigated. The simulated and measured results show that the RCS of the microstrip printed dipole antenna with the proposed DUC-EBG ground is much lower than that of the antenna with the conventional metallic ground at frequencies outside the operating band within 1–8 GHz, while its radiation is hardly affected by the proposed DUC-EBG ground in the operating band. Owing to the stop-band property of the proposed DUC-EBG, it can be used as the ground plane of a microstrip printed dipole antenna. During the pass-band, the proposed DUC-EBG can make much more incident wave pass through. Therefore, it can effectively reduce the RCS of microstrip printed dipole antenna outside operating band.

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 Novel Two-Dimensional Extrapolation Technique for Fast and Accurate Radar Cross Section Computation

In this letter, a novel two-dimensional (2-D) extrapolation technique for the approximation of three-dimensional (3-D) radar cross section (RCS) pattern is presented. The best uniform rational approximation, performed by the Maehly approximation, is applied to the method of moments (MoM) to predict the 3-D monostatic RCS pattern. Compared to the asymptotic waveform evaluation (AWE) technique, the major advantage of the Maehly approximation is that it can avoid calculating derivatives of the dense impedance matrix and excitation matrix, and it is accurate in much broader frequency domains and spatial domains. Numerical results show that the proposed method is superior in terms of CPU time compared to the traditional MoM. Good agreement between the proposed technique and the traditional MoM is observed.

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.

The Design and Performance of a Novel Square-Loop Patch Frequency Selective Surface

A novel stop-band Frequency selective surface (FSS) is presented. By adding four narrow branches to conventional square-loop FSS, the proposed FSS can achieve a good frequency stability for different oblique angles and a high frequency selective ability. An equivalent circuit model is used to simply analyze its transmission property. The good agreement between simulated and measured results shows the validation of our design.

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.

Fast and Accurate Radar Cross Section Computation Using Chebyshev Approximation in Both Broad Frequency Band and Angular Domains Simultaneously

To predict the three-dimensional radar cross section (RCS) pattern of an arbitrary shaped perfectly electric conductor objects in both a broad frequency band and angular domains simultaneously, the method of moments (MoM) combined with the Chebyshev polynomial approximation is presented. The induced current is expanded by a bivariate Chebyshev series. Using this function, the induced current can be obtained at any frequency and angle within the desired frequency band and angular domains. Numerical results show that the proposed method is found to be superior in terms of the CPU time to obtain the three-dimensional RCS pattern compared with the direct solution by MoM repeating the calculations at each frequency and angle. Good agreement between the presented method and the direct MoM is observed.