Yun-e Xu

A NOVEL ULTRA-WIDE BAND ANTENNA WITH REDUCED RADAR CROSS SECTION

A novel printed dual circular ring monopole antenna with low radar cross section (RCS) for ultra-wide band (UWB) application is proposed. The proposed antenna is designed to realize RCS reduction. The two circular rings are connected by several metallic via holes to improve the radiation characteristics of the proposed antenna. Its UWB-related characteristics are simulated and experimentally verifled. The RCS performance of the proposed antenna under difierent loads is studied and compared with that of a commonly used circular- disc monopole antenna. The results show that the proposed antenna has good radiation performances and lower RCS than the reference antenna. The proposed antenna serves as a good candidate in the design of UWB antenna with the requirement of RCS control.

Wideband Omnidirectional Circularly Polarized Patch Antenna Based on Vortex Slots and Shorting Vias

A wideband omnidirectional circularly polarized (CP) microstrip antenna is proposed. The proposed antenna is composed of a disk-loaded coaxial probe, six shorting vias and a circular patch with six vortex slots. Three resonant modes, which include the TM01, top-loaded monopole and TM02 modes, with conical radiation patterns can be simultaneously excited in the antenna structure by a disk-loaded coaxial probe through capacity coupling, and they can be coupled together to realize a wideband operation. Six shorting vias, located symmetrically about the center of the patch, are introduced for generating the θ-polarization and six vortex slots are employed for obtaining the φ-polarization. Omnidirectional CP fields can be obtained at all these three resonant modes when the two orthogonal polarizations are equal in amplitude but different in phase by 90°. Both the wideband and CP principles are analyzed and verified by the parametric study. The obtained results show that the wideband CP antenna has a 10-dB impedance bandwidth of 51.7% and a 3-dB axial ratio (AR) bandwidth of 57.8%. In addition, a comparison between the proposed wideband antenna and the related wideband CP antennas in the literature is made.

Radiation Pattern Synthesis for Arrays of Conformal Antennas Mounted on an Irregular Curved Surface using Modified Genetic Algorithms

An E-shaped conformal microstrip antenna array mounted on an irregular curved surface which is similar to an aerocraft cavity in shape is developed in this paper. In view of the narrow bandwidth of the microstrip antenna, an E-shaped element is applied instead of the traditional rectangular element. Furthermore, an element structure of uneven thickness is adopted in order to take into account the effects of the carrier on the resonance frequency and bandwidth of the conformal array. Then, an 8-element conformal microstrip antenna array is designed and the radiation pattern is synthesized using the modified genetic algorithms (MGAs). Compared with the standard genetic algorithms (SGAs), MGAs has a much more fast convergence speed and need less computational time to reach the expected value. The result shows that the optimized azimuth radiation pattern is almost omnidirectional and the elevation radiation pattern is concentrated in the horizontal direction. It can be seen that the proposed method of MGAs is an effective means for designing the conformal antenna array on an irregular curved surface.

Fast Shadowing Technique for Electrically Large Targets Using Z-Buffer

An improved fast shadowing technique fit for the calculation of electromagnetic field is proposed in this paper based on the shadowing technique of z-buffer in computer graphics. The traditional shadowing algorithm consumes too much time, for it is necessary to judge the shadowing relationship of every two facets. The proposed algorithm combining z-buffer with traditional algorithm falls into the shadowing processing using triangle facet modeling. The problem of great time consumption in shadowing judgment for electrically large targets is well solved through proper subdivision of buffer and localization of judgment within facets in the surrounding buffer elements. The proposed arithmetic has great advantages over the traditional one, especially in its high running speed. This improved technique is tested to be valid in that it remarkably increases the computation speed on the premise of satisfying the precision requirement.

A New Method for Broadening Bandwidths of Circular Polarized Microstrip Antennas by Using DGS & Parasitic Split-Ring Resonators

A new method for broadening the impedance and the axialratio (AR) bandwidths of circular polarized microstrip antennas (CPMAs) is proposed. It has improved the bandwidths of a reference antenna greatly without enlarging the antenna size or deteriorating circular polarized radiation characteristics by placing four sequentially rotated parasitic split-ring resonators (SRRs) around the patch of the reference antenna and embedding four defeated ground structure (DGS) elements on the ground plane. Improvements of 51.3% and 49.8% in the impedance and the axial-ratio bandwidths of the antenna are achieved in simulation, respectively. The simulated i10dB impedance and 3dB axial-ratio bandwidths of the antenna have been improved from 101.1MHz (4.12%) to 153.0MHz (6.26%) and from 25.1MHz (1.02%) to 37.6MHz (1.54%).

Efficient Wide-Band Analysis of Antennas Around a Conducting Platform Using MoM-PO Hybrid Method and Asymptotic Waveform Evaluation Technique

An efficient wide-band analysis that combines method of moments-physical optics (MoM-PO) hybrid formulation with the asymptotic waveform evaluation (AWE) technique is presented for antennas around an electrically large platform. To facilitate the analysis of large problems, compared with MoM, the MoM-PO hybrid formulation is employed to reduce the number of unknowns and memory requirements. Further, the automatic differentiation (AD) approach is used to calculate the high order frequency derivatives of Greens functions required in the algorithm. Numerical results show the efficiency and capability of the method proposed in this paper.

Circularly Polarized Slot Microstrip Antenna for Harmonic Suppression

With the introduction of the circularly symmetrical slot near the coaxial feed location of the corner truncated square microstrip antenna patch, both the circular polarization and harmonic suppression performance can be realized in this antenna. Effectiveness of the circularly symmetrical slot for harmonic suppression is studied, including its affection to circular polarization performance of the antenna. Experimental results show that application of the circularly symmetrical slot near the coaxial feed location of the microstrip antenna patch can remarkably suppress the harmonic frequencies. Measured radiation patterns indicate that the forward radiation is suppressed by more than 10~20 dB at the second and the third harmonic frequencies compared to the reference antenna, while maintaining the circular polarization performance, the cross polarization, and the backward radiation.

Isolation Enhancement in Patch Antenna Array With Fractal UC-EBG Structure and Cross Slot

A compact patch antenna array with high isolation by using two decoupling structures including a row of fractal uniplanar compact electromagnetic bandgap (UC-EBG) structure and three cross slots is proposed. Simulated results show that significant improvement in interelement isolation of 13 dB is obtained by placing the proposed fractal UC-EBG structure between the two radiating patches. Moreover, three cross slots etched on the ground plane are introduced to further suppress the mutual coupling. The design is easy to be manufactured without the implementation of metal vias, and a more compact array with the edge-to-edge distance of 0.22 λ0 can be facilitated by a row of fractal UC-EBG, which can be well applied in the patch antenna array.

Efficient IE-FFT and PO Hybrid Analysis of Antennas Around Electrically Large Platforms

An efficient hybrid analysis that combines integral equations (IE) with physical optics (PO) approximation is presented for antennas around an electrically large platform. In the analysis, the whole surface of the platform and antennas is divided into two regions, namely, the full-wave region and the PO region. In the full-wave region, the IE is modified by coupling into the PO contribution. Similar to the fast IE method, the modified impedance matrix is decomposed into the near-field couplings and the well-separated group couplings, respectively. By interpolating the Greens function, the couplings between two well-separated groups can be computed using fast Fourier transform (FFT). Due to the PO approximation, the hybrid method utilizes fewer unknowns and requires less solution time than the conventional IE-FFT.

ANALYSIS OF SHADOWING PROCESSING TECHNIQUE BASED ON MODELING USING NURBS

The shadowing relationship between facet elements can be determined rapidly through analytical expressions. On the basis of modeling using curved surfaces, an effective shadowing processing algorithm is proposed which is in combination with that used in the shadowing judgement of facet elements. Firstly several sampling points are taken on the ergodic curved surface element to construct a group of facet elements, which can replace the curved surface element. Then the shadowing processing between the stationary phase point and the ergodic curved surface element is converted to that between the stationary phase point and several facet elements, thus avoiding utilizing optimization method and can increase the computation speed. Similarly, the shadowing processing between the stationary phase segment and the ergodic curved surface element is converted to that between the stationary phase segment and several facet elements. And the trimming algorithm is used to accurately find the visible part of the stationary phase segment, which gets rid of the rough shadowing processing technique that determines the visibility of the whole stationary phase segment through the visibility of the center of the stationary phase segment. Therefore, the computation precision is greatly improved. When there exists a huge number of curved surfaces, maximum-minimum preprocessing is utilized to increase the computation speed. Examples show that this novel algorithm is superior to the traditional one in both computation speed and precision.