Near-field blockage of an ultralow sidelobe antenna

An analytical model is presented which describes the farfield radiation pattern of an array antenna blocked by a vertical or horizontal metallic cylinder in the near field of the aperture. The implementation of this model as a generalized computer program has been completed, and the computed radiation patterns have been verified by extensive measurements on a low sidelobeX-band slotted waveguide array. The effects of the blockage are summarized graphically for a wide range of obstacle sizes and distances, and for aperture illuminations ranging from conventional reflector-type distributions to ultralow sidelobe distributions. Using dielectric or absorptive coatings to improve the radiation pattern in the presence of cylindrical obstacles is proposed as a logical extension to the existing model.     

一种太赫兹波段宽带反射型极化变换器

提出了一种由表层矩形金属周期图案、聚酰亚胺薄膜基底和金属反射面组成的新型反射型极化变换器。为了降低极化变换器对基底厚度的敏感度,增大工作带宽,该设计采用将传统反射型极化变换器表层金属线栅开口截断和增大金属线栅宽度的方法,引进了表层金属图案对两正交极化方向电磁场的等效电容电感效应,进行相位调制。仿真结果表明中心频率为500 GHz时,工作带宽可达到140 GHz,插入损耗小于0.5 dB,并且在一定基底厚度条件下误差在一定范围内,整体性能几乎无变化。仿真表明该极化变换器有效增大了工作带宽,并降低了对基底厚度敏感度。提出了薄膜光刻工艺来对设计的极化变换器进行加工制作。     

A reconfigurable aperture antenna based on switched links between electrically small metallic patches

A reconfigurable aperture (RECAP) antenna is described in which a planar array of electrically small, metallic patches are interconnected by switches. The antenna can be reconfigured to meet different performance goals by changing the switches that are open and closed. The switch configuration for a particular goal is determined using an optimizer, such as the genetic algorithm. First, the basic concept for the RECAP antenna is verified by comparing theoretical results with measurements for configurations in which the switches are simply wires connecting the patches. Next, details are given for a prototype antenna in which field-effect transistor based electronic switches are used with optical control. Theoretical results for the prototype antenna are then compared with measurements for cases in which electronic reconfiguration is used to change the bandwidth of operation or steer the pattern of the antenna. Finally, an overview of alternate switch/control strategies, some of which were tested, is given along with suggestions for improving the next generation of this antenna.     

Yagi-Uda Array as a Surface-Wave Launcher for Dielectric Image Lines

A Yagi-Uda array of monopoles is embedded in the dielectric of a dielectric image line, with the driven element fed from coaxial cable below the metallic ground plane, in order to launch the dipole-mode surface wave. The launching efficiency is a function of the array length and is relatively independent of the transverse dimension. With a six-element array, a launching efficiency of 62 percent has been achieved over an 18-percent bandwidth at 2.2 GHz. A design procedure for such arrays is described and experimental verification is given.     

基片集成脊波导传输特性的研究

将构成基片集成脊波导脊的一排金属针等效成实金属脊。基于基片集成波导等效宽度计算公式推导了基片集成脊波导等效脊宽的计算公式。运用横向谐振法推导了TEm0模基片集成脊波导截止频率的计算公式,同时运用这些公式分别计算了TE10模、TE20模和TE30模基片集成脊波导的截止频率,并与仿真软件计算的结果和参考文献所给结果进行了比较。结果显示:利用所给公式计算的结果具有较高的精度,且使用方便。此外,还研究了截止频率与脊宽和脊隙之间的关系,对一种适合宽带应用的宽脊结构进行了讨论。     

EMC prediction model of a single wire transmission line crossing acircular aperture in a planar screen

The structure composed by a wire running above a ground plane and passing through an aperture in a semi-infinite metallic screen is analyzed from an electromagnetic point of view. We assume that the distance between the wire and the ground plane is sufficiently greater with respect to the aperture dimensions and that the latter are small in comparison with the free-space wavelength. A very accurate low frequency solution is obtained by representing the field quantities in a suitable spectral domain and by treating the wire current as a filament current. A transmission line model of the structure, based on the scattering parameter representation for both internal and external excitation, is derived. Then, by use of such a model, analytical expressions for an insertion loss and a signal-to-noise ratio (SNR) are obtained in order to assess the electromagnetic compatibility of the structure     

Analysis of directive radiation from a line source in a metamaterial slab with low permittivity

In this paper an investigation is presented of metamaterial structures excited by a line source aimed at producing narrow directive beams. The structure under consideration is a grounded slab made of a homogeneous metamaterial medium with a plasma-like dispersive permittivity; for low values of the slab permittivity an extremely directive beam pointing at broadside can be obtained. Conditions for the maximization of radiation at broadside are given and the narrow-beam effect is shown to be related to the excitation of a leaky mode supported by the slab, with radiation maximization corresponding to small and equal values of the phase and attenuation constants. The frequency bandwidth and directivity are expressed in a simple closed form in terms of the attenuation constant of the leaky mode. By increasing the slab height for a fixed frequency, the leaky mode is analytically shown to give rise to a beam that is scanned from broadside to the critical angle for plane-wave refraction, thus being confined to a narrow angular region around broadside. Numerical results are given that illustrate these features, and full-wave simulations of a metamaterial structure made of an array of metallic cylinders are presented that confirm the results of the analytical study. The case of a line source inside a semi-infinite metamaterial region is also considered and its radiation characteristics compared with those of the metamaterial slab.     

Phase modulation of a loop phase-locked grid oscillator array

In this letter, we describe a method for phase modulation of a loop phase-locked grid oscillator array and report results obtained in a test bed implementation of the method. The key to the scheme lies in introducing the phase-locked loop (PLL) in such a way that the modulating data stream is introduced in parallel with the loop rather than through it, thereby circumventing the bandwidth limitation of the PLL. The experiment was performed at 4.7 GHz with a phase-locked grid oscillator array. The grid oscillator was successfully modulated by a 1 MHz signal, which is ten times higher than the bandwidth of the phase-locked loop     

A broad-band twist reflector

Polarization twisting reflectors, or twist reflectors, consisting of a wire grid spaced approximately3 lambda/8from a ground plane [1], [2] have a bandwidth of at most 30 percent. It is shown that the inclusion of an additional wire grid in front of the first grid makes bandwidths of 100 percent possible. Design formulas, theoretical performance in terms of cross polarization attenuation, and some experimental results for a twist reflector with two wire grids are given.     

Optimization of linear arrays for broadband signals

The effect of broadband signals on the far-zone field of long arrays is investigated in terms of the energy radiation pattern. A generalized directive gain is introduced which depends on the signal spectrum. With maximum directivity as a criterion it is shown that the problem of optimizing a long isotropic array with respect to a given signal can be associated with a classical eigenvalue problem. The concept of array-bandwidth is introduced. Computed curves for directivity and directive gain are given in terms of this parameter and signal bandwidth. It is shown that while little improvement in directivity is achieved by optimizing the distribution coefficients of an array, a substantial reduction in sidelobe level is obtained when the signal bandwidth is comparable to the array bandwidth.     

铁磁性基体与金属线阵列复合体系的双负材料特性

基于铁磁性基体与金属线阵列复合结构等效电磁参数的长波近似模型,设计了一种应用铁磁性基体的二维双负材料。根据带有介质包裹层的金属线的散射特性,采取多重散射方法计算了铁磁性基体与金属线阵列复合结构的传输谱;还通过全波仿真提取了单元结构的等效电磁参数。这些数值结果与长波近似模型的理论结果取得了很好的一致,确认了该模型的正确性。通过仿真周期复合体系中的电磁场分布,在所设计的双负频带内观察到了反向波现象,进一步验证了所设计的复合体系的双负特性。     

宽带单脊波导缝隙天线阵设计

给出了一种新型脊波导宽边缝隙天线阵设计,天线阵被分成几个子阵形式,通过膜片的激励方式,由一个半高波导功分器馈电.设计、加工了一根16元波导天线阵,测试得到11.3%的阻抗带宽(VSWR＜1.5),天线辐射方向图最大副瓣电平低于-12 dB,具有低于-40 dB的交叉极化特性.     

基于遗传算法的栅格天线阵旁瓣电平优化方法

在推导出栅格天线阵列方向图的基础上,提出一种基于遗传算法的栅格天线阵旁瓣电平优化的方法。此方法首先简化栅格天线阵物理模型,给出等效模型下的阵列方向图,然后以栅格天线阵的短边电流幅度为优化参量,以阵列天线方位面的副瓣电平为适应度函数,利用遗传算法的最优化搜索得到满足副瓣要求的电流幅度,再通过电流幅度计算辐射单元阻抗,最终设计出满足要求的低旁瓣栅格天线阵。为了验证该方法的有效性,对一种频扫微带栅格天线进行了优化,在电磁仿真软件中对优化后的天线进行了仿真,根据设计结果加工制作了原型天线并进行了测试,测试结果显示优化后天线阵的副瓣电平降低了5dB,优化效果明显。     

Bandwidth improvement for a microstrip-fed series array ofdielectric resonator antennas

The impedance and pattern bandwidth of an array of dielectric resonator antennas series fed by a microstrip line was significantly improved by replacing individual DRAs with paired DRAs. The DRAs in each pair are spaced slightly <λ_g/4 apart so that their input reflections cancel. An array of eight DRA pairs was designed and fabricated, and its performance was compared to an array of eight single elements. The 10 dB return loss bandwidth improved from 2 to 18% and the 3 dB gain pattern bandwidth improved from 12 to 17%     

Dual-loop slot array antenna radiating circularly polarised wave

An array antenna consisting of dual-loop slot elements with a simple feeding system is realised. Each dual-loop element has two loop slots that are simultaneously fed by a single triplate transmission line. A narrowed beam, of circular polarisation, with an axial ratio of less than 3 dB, is obtained over a 3% bandwidth. The measured radiation pattern agrees well with a pattern calculated using array theory.<>     

Broadband quasi-microstrip antenna

A new printed microwave antenna is presented. The antenna is a hybrid between a wire antenna array and a microstrip patch antenna. Although the size, cost, and efficiency are comparable to the microstrip patch, the voltage standing wave ratio 2:1 bandwidth of the antenna presented here is above 20%. The radiation pattern of the antenna does not change appreciably within the bandwidth, and the theoretical efficiency for optimal antennas remains above approximately 80% within the bandwidth. Measurements on several antennas around 2 and 4 GHz are presented, as well as theoretical results obtained using a full-wave analysis     

Efficient classification by neural networks using encoded patterns

The corners and the middle points, which are extracted as features from the line approximation of a given pattern, are overlaid on a radial grid to form the input array for training a backpropagation network for classification. The proposed method is shown to be simple and robust by extensive testing of its performance on patterns both with and without noise     

Reactively steered adaptive array using microstrip patch elements at 4 GHz

A reactively steered adaptive array (RESAA) has one element connected by a transmission line to a receiver and a number of closely spaced parasitic elements, each of which is terminated by an adjustable reactive load. The pattern is formed by control of the reactive loads. Experimental results and the theory are presented for a RESAA consisting of five microstrip rectangular patch elements resonant at 4.0 GHz. Using steepest descent control of the reactive loads in a power inversion mode (no reference), we find that a null with a depth of 30 dB (relative to the pattern maximum) and an angular width of about25degcan be steered towards an interferer. Typically, about 40 steps (iterations) are needed for forming the null. With the slow power meter and general purpose minicomputer that served as the controller, adaptation times of several seconds are required; extrapolation to a dedicated microprocessor controller predicts adaptation times of several milliseconds. Operation in a mode using a reference signal demonstrates that the pattern can be shaped to steer a null toward interference and a lobe towards a desired signal. The nulling bandwidth is approximately 40 MHz with this array. The advantages of a RESAA, as compared With a conventional adaptive array, include the elimination of the mixers and other hardware needed to perform the complex weighting of the output of each element at an intermediate frequency, and better pattern control for closely spaced elements. These advantages are obtained at the expense of a more complicated control algorithm.     

A new 2-D model for operating point shift in large LWIR HgCdTeFPA's

Infrared focal plane arrays (IRFPAs) are rapidly increasing in size. It is shown here that for large FPAs a considerable shift in the operating point occurs, which, if not reduced, introduces unacceptably large nonuniformity in the array response. This shift results because of the variable voltage drop across the HgCdTe active layer, due to its finite distributed resistance. A new analytical two-dimensional (2-D) model to estimate the operating point shift of individual detectors of long wavelength infrared (LWIR) HgCdTe focal plane array (FPA) is presented. Avoiding this operating point shift requires an optimized grid pattern     

An electromagnetic-field method modeling of a radial line planar antenna with coupling probes

This communications describes an electromagnetic model of a radial line planar antenna consisting of a radial guide with one central probe and many peripheral probes arranged in concentric circles feeding an array of antenna elements such as patches or wire curls. The model takes into account interactions between the coupling probes while assuming isolation of radiating elements. Based on this model, computer programs are developed to determine equivalent circuit parameters of the feed network and the radiation pattern of the radial line planar antenna. Comparisons are made between the present model and the two-probe model developed earlier by other researchers.