Statistically designed density-tapered arrays

The design of "thinned" planar array antennas is considered in which the density of elements located within the aperture is made proportional to the amplitude of the aperture illumination of a conventional "filled" array. Density tapering permits good sidelobe performance from arrays of equally radiating elements. The selection of the element locations is performed statistically by utilizing the amplitude taper as the probability density function for specifying the location of elements. The statistical design procedures and the theoretical prediction of performance are given. Application to a 50 wavelength diameter planar aperture is discussed and the results compared to conventional amplitude-taper designs. Examples of computed patterns are shown for density tapers modeled after 25, 30, 35, and 40 db circular Taylor distributions. The properties of a planar array of 10,000 elements are examined for "natural" thinning and for 70 per cent and 90 per cent of the elements removed. The sidelobes are determined more by the number of remaining elements than by the model amplitude taper. Statistically designed density-tapered arrays are useful when the number of elements is large and when it is not practical to employ an amplitude taper to achieve low sidelobes.     

共享孔径同心圆阵稀疏交错优化布阵方法

同心圆阵列天线具有波束对称、360°方位角扫描、抗干扰能力强等优点，被广泛应用于星载、机载、舰载雷达及飞机声呐等领域。在天线孔径有限的情况下，如何进一步提高同心圆阵的孔径利用率，通过孔径的空分复用，设计出子阵稀疏交错分布的多功能同心圆阵列天线，具有较大的研究价值。利用均匀同心圆阵列天线激励与方向图函数存在二维傅里叶-贝塞尔变换关系，基于二维三次插值和密度加权，提出了一种同心圆阵稀疏交错优化布阵的方法。该方法通过对均匀同心圆阵列天线方向图采样值的频谱能量进行分析，采用三次插值的方法，实现了同心圆天线阵列方向图函数到同心圆阵元激励能量的映射转换；基于密度加权的原理，对排序后归一化阵元激励的奇偶交错选取，使得稀疏交错子阵方向图频谱能量均分匹配，实现了同心圆阵的稀疏交错优化布阵设计。仿真结果表明，该方法得到的交错子阵天线具有峰值旁瓣电平低、主瓣宽度窄且方向图性能近似程度高的优点，有效解决了同心圆阵列天线稀疏交错优化布阵的设计难题，实现了两子阵交错的共享孔径多功能同心圆阵列天线设计。     

Thinned arrays using genetic algorithms

Large arrays are difficult to thin in order to obtain low sidelobes. Traditional statistical methods of aperiodic array synthesis fall far short of optimum configurations. Traditional optimization methods are not well suited for optimizing a large number of parameters or discrete parameters. This paper presents how to optimally thin an array using genetic algorithms. The genetic algorithm determines which elements are turned off in a periodic array to yield the lowest maximum relative sidelobe level. Simulation results for 200 element linear arrays and 200 element planar arrays are shown. The arrays are thinned to obtain sidelobe levels of less than -20 dB. The linear arrays are also optimized over both scan angle and bandwidth.<>     

Position-modulated phased array-space factor considerations

The space factor of an element position-modulated array is expressed as an Anger function series for a general amplitude distribution. The behavior of the main lobe and the diffraction sidelobes for uniform excitation are presented in the form of universal curves. It is found that the nulls near the main lobe disappear for the modulation index above a critical value. The peak level of the grating plateaus and their shapes are given in terms of approximate expressions and are exactly determined computationally. The nature of the curves suitable for design of such arrays for a given scan range and permissible peak sidelobe level is given. An example shows that a high resolution beam may be obtained with a comparatively smaller number of elements than required by a uniformly illuminated periodic array. An exact-series summation formula for the directivity of nonuniformly spaced antenna arrays of isotropic elements is given. The directivity of the modulated array computed by this formula shows a smooth variation at the ends of the scan range in contrast to the sudden fall in the case of the periodic array.     

Switchable end-fire element for three-dimensional array use

Use of interpolation processor coefficients as weights in a particular line array format leads to an end-fire pattern having special properties. A wide, nearly constant gain main beam results which is complemented by a backside region having uniformly low peak sidelobe levels. Changing the polarity of one element reverses the direction of energy flow. Use of these simple line arrays as elements of a planar array permits elimination of the back-screen and offers bidirectional coverage. An overview of the technique is presented along with some design examples.     

Reduction of sidelobes in uniformly excited arrays with element pattern control

Uniformly excited arrays of identical elements suffer from high close-in sidelobes. Suppression of sidelobe levels can be achieved by tapering the aperture amplitude distribution, but a more complex feed network results. A novel form of amplitude tapering is described, in which element pattern control in uniformly excited arrays is shown to theoretically reduce close-in sidelobe levels.     

基于遗传算法和模拟退火的不等间距稀布阵的设计

副瓣电平在天线阵列的设计中是很重要的指标,已经有很多方法进行这方面的改进。该文在稀布阵概念的基础上,引入了距离微扰,提出不等间距稀布阵的模型,来进一步改善天线阵的副瓣电平,并且利用遗传算法和模拟退火对这种不等间距稀布阵进行了综合设计。给出了200元线阵和4020面阵的优化结果,从仿真结果可以看到天线副瓣电平得到了改善。     

A numerical pattern synthesis algorithm for arrays

A numerical technique for pattern synthesis in arrays is presented. For a given set of elements, the technique allows one to find a set of array coefficients that steer the main beam in a given direction and yield sidelobes meeting a specified criterion, if such a set of array coefficients exists. If the pattern specifications cannot be met with the given elements, the algorithm finds the best attainable pattern. The advantage of this technique is that it can be used with an arbitrary set of array elements. Different elements in the array can have different element patterns, and the array can have arbitrary nonuniform spacing between elements. The synthesis technique is based on adaptive array theory. The given array elements are assumed to be used as the elements of an adaptive array. The main beam is pointed in the proper direction by choosing the steering vector for that direction, and the sidelobes are controlled by introducing a large number of interfering signals at many angles throughout the sidelobe region. The algorithm iterates on the interference powers until a suitable pattern is obtained     

Aerial arrays with asymmetrical thinning

The use of asymmetrical element spacings in thinned aerial arrays is shown to give symmetrical radiation patterns. The use of asymmetrical element spacings gives lower sidelobe levels than symmetrical spacings. With an array of nine elements in a 19? array, the greatest sidelobe level is reduced from ?5.61 dB to ?6.87 dB by using an asymmetrical array instead of a symmetrical array.     

New Model for Synthesis of Symmetrical Thinned Linear Arrays

In symmetrical thinned linear arrays design, the positions of thinned array elements are very important for optimal performance in terms of its minimum peak side lobe level (Msll). For the synthesis of thinned arrays with a given thinning rate, it would have almost the same Msll solution between taking only segmental aperture nearby both ends of the aperture into account and taking all the aperture into account. In this paper, the element distribution characteristic over the aperture of many optimum thinned arrays is studied, then the aperture release model is founded by the least square method to synthesize the thinned arrays. This model is vital for the computing burden alleviation and the efficiency optimization, and would hardly bring any degradation of the obtained array performance.     

The Pareto Optimization of Ultrawideband Polyfractal Arrays

The application of global optimization techniques, such as genetic algorithms, to antenna array layouts can provide versatile design methodologies for highly directive, thinned, frequency agile, and shaped-beam antenna systems. However, these methodologies have their limitations when applied to more demanding design scenarios. Global optimizations are not well equipped to handle the large number of parameters used to describe large- antenna arrays. To overcome this difficulty, a new class of arrays was recently introduced called polyfractal arrays that possess properties well suited for the optimization of large- arrays. Polyfractal arrays are uniformly excited with an underlying self-similar geometrical structure that leads to aperiodic element layouts. This paper expands on polyfractal array design methodologies by applying a robust Pareto optimization technique with the goal of reducing the peak sidelobe levels at several frequencies specified over a wide bandwidth. A recursive beamforming algorithm and an autopolyploidy based mutation native to polyfractal geometries are used to dramatically accelerate the genetic algorithm optimization process. This paper also demonstrates that the properties of polyfractal arrays can be exploited to create designs that possess no grating lobes and relatively low sidelobe levels over ultrawide bandwidths. The best example discussed in this paper maintains a dB peak sidelobe level with no grating lobes from a , to more than a minimum spacing between elements, which corresponds to at least a 40:1 bandwidth for the array.     

New Model for Synthesis of Symmetrical Thinned Linear Arrays

In symmetrical thinned linear arrays design, the positions of thinned array elements are very important for optimal performance in terms of its minimum peak side lobe level （Msli）. For the synthesis of thinned arrays with a given thinning rate, it would have almost the same Msll solution between taking only segmental aperture nearby both ends of the aperture into account and taking all the aperture into account. In this paper, the element distribution characteristic over the aperture of many optimum thinned arrays is studied, then the aperture release model is founded by the least square method to synthesize the thinned arrays. This model is vital for the computing burden alleviation and the efficiency optimization, and would hardly bring any degradation of the obtained array performance.     

Comparison between the peak sidelobe of the random array and algorithmically designed aperiodic arrays

Thinned arrays (mean interelement spacing greater than one-half wavelength) are made aperiodic to suppress grating lobes. Many thinning algorithms were created in the 1960's and tested by computer simulation. Seventy such algorithmically designed aperiodic arrays are examined and the distribution of their peak sidelobes, relative to the expected values for random arrays having the same parameters, is obtained. The distribution is compared to that of a set of 170 random arrays. Both distributions are found to be nearly log normal with the same average and median values. They differ markedly in their standard deviations, however, the standard deviation of the random array distribution (1.1 dB) is approximately half that of the algorithmic group. The compactness of the random distribution almost guarantees against selection of a random array with catastrophically large peak sidelobes. Among the several algorithms examined, the method of dynamic programming produced the lowest peak sidelobe on the average.     

Array pattern control and synthesis

Antenna array distributions and their associated patterns are now designed on physical principles, based on placement of zeros of the array polynomial. An overview of the synthesis processes is given. Robust and low Q distributions for linear arrays and circular planar arrays that provide variable sidelobe level pencil beam patterns are treated in detail. Associated difference patterns are included. Individual sidelobes or groups of sidelobes may be adjusted in level. The same technique allows synthesis of an efficient shaped beam, with or without sidelobe adjustment. The ultimate pencil beam array, the superdirective array, is evaluated     

Thinned coincident arrays for the direct measurement of the principal solution in radio astronomy

A new technique is described for the design of a thinned, linear, multiplicative array which directly measures the principal solution of a radio source distribution. The original filled multiplicative array with uniform element spacing /spl lscr/ is first generalized to an array of N/sub 1/+1 subarrays each with M/sub 1/+1 elements. A thinning factor of 1/2 is shown to be possible if M/sub 1/=N/sub 1/. Finally, if each subarray is further divided into smaller subarrays until the smallest are simply two element interferometers, then the principal solution can be directly measured but with far fewer elements. Significant thinning factors are achieved when the array is very large. The method can also be used to measure the principal solution with planar arrays, with very strong thinning occurring for large arrays.     

Sidelobes control of solid-state array antennas

An aperture design is described for two-dimensional (2-D) solid-state phased arrays that transmits low sidelobes. A five-step amplitude distribution for the aperture was optimized by a gradient search method to achieve -36-dB peak sidelobes. The optimized configuration was applied to a sample array of 36 columns by 14 rows, with 400 modules divided into five groups of power levels. The array performance with the actual module lattice structure taken into account is discussed. Gain drop and sidelobe degradations due to random amplitude and phase errors are also studied     

Sidelobe reduction of circular arrays with a constant excitation amplitude

It is shown that the sidelobe level of circular arrays with a constant excitation amplitude can be reduced by adjusting the excitation phases of array elements. The resulting radiation pattern has equal-ripple sidelobes similar to a Chebyshev pattern. Examples are given.     

基于格理论的非均匀稀疏线阵旁瓣结构的分析方法

 在有限个阵元的情况下,非均匀稀疏线阵能得到更大的阵列孔径。但由于其是对空间信号的非均匀采样,不能通过常规的傅立叶变换方法求得其峰值旁瓣解析表达式。本文提出了一种基于格理论的非均匀稀疏线阵的旁瓣结构分析方法。首先建立了阵列流形格的数学模型并对其物理含义进行了仿真分析,然后推导了阵列流形格最近格点与峰值旁瓣的对应关系,从而将非均匀稀疏线阵峰值旁瓣结构分析问题转化为求距阵列流形格原点最近格点问题。该方法可以准确地确定非均匀稀疏线阵旁瓣中增益大于门限电平的旁瓣个数及其各自的方位。计算机仿真结果表明了该方法的有效性和准确性。     

利用GA实现非对称稀疏线阵旁瓣电平的优化

该文讨论运用遗传算法综合非对称的稀疏直线阵列(阵元从规则栅格中稀疏)。阵元在中心两侧非对称分布的布阵方式提供了可利用的优化自由度,将更有利于提高稀疏阵列的性能。构造了阵元关于阵中心非对称时优化旁瓣电平的适应度函数,仿真结果表明,无对称约束的阵元排列,不仅可以进一步抑制稀疏线阵的相对旁瓣电平(RSLL),而且当阵列由有向阵元组成时,有益于改善阵列波束扫描过程中RSLL的恶化。     

On a simple method of obtaining sidelobe reduction over a wideangular range in one and two dimensions

A patented technique for suppressing the sidelobes of an array antenna is considered. This technique involves the addition of two elements, one at each end of the array, which together produce an interferometer pattern used for the cancellation of sidelobes. It is shown here that the technique is most effective for uniform illumination and that there then exists an optimum fixed position for the added elements. The amplitude of the excitation of the auxiliary elements determines the angular location of the region of sidelobe reduction while the phase of the excitation tracks the beamsteering phase of the array. Thus, this technique is seen to be easily implemented in an array controlled by coupled oscillators. The technique generalizes in a straightforward manner to two-dimensional (2-D) arrays in which case a set of auxiliary elements on the perimeter of the array is required. A 2-D oscillator controlled array of this type is described here with which one can produce a main beam and a sidelobe suppression region that can be independently positioned anywhere in a hemisphere provided they do not coincide