A contoured beam synthesis technique for planar antenna arrays withquadrantal and centro-symmetry

A method is described for the synthesis of planar array antennas with prescribed contoured beams. The technique utilizes a transformation which divides the problem into two decoupled subproblems. One subproblem involves the determination of certain coefficients of the contour transformation in order to achieve the required footprint contours. The number of coefficients which need to be used depends on the complexity of the desired contour, but is very small in comparison to the number of planar array elements. The other subproblem consists of a linear array shaped beam synthesis, for which there already exist powerful methods for determining appropriate element excitations. The size required for this prototype linear array depends on the number of contour transformation coefficients used and the size of the final planar array. Simple formulas then determine the final planar array excitations from the information forthcoming from the above two subproblem solutions     

Very fast method to synthesise conformal arrays

Avery fast technique that allows the synthesising of arbitrary footprint patterns by using conformal arrays with many radiating elements is described. This method is based on a combination of Woodward-Lawson and Elliott-Stern techniques, and it was applied to the synthesis of a triangular footprint generated by 657 axial dipoles placed on a cylindrical surface, obtaining acceptable ripple and sidelobe levels.     

基于投影矩阵法的阵列天线波束形成方法

该文介绍一种阵列天线波束形成的新算法投影矩阵法,包括复系数、仅相位、仅幅度的波束形成技术,并推广应用到多目标波束综合设计中。文中首先给出采用投影矩阵法进行阵列天线复系数和仅相位波束形成的计算方法,然后提出仅幅度控制下的投影矩阵法,并进一步应用到多目标波束同时优化设计中。该文计算了多种工程应用例子,特别是满足全口径和多子孔径波束优化的仅幅度控制技术、满足多波束优化的仅相位控制及共用幅度优化技术,对算例的设计达到了采用优化激励系数控制波束指向、波束赋形、旁瓣电平等性能要求,实现了阵列天线的波束形成。仿真结果说明了投影矩阵法的有效性,适用范围广泛。      

Reflector radiation pattern from planar near-field measurements of array feed

High gain shaped beam antennas for satellite frequency reuse applications are almost exclusively obtained by the use of complex multielement feed arrays to provide pattern control in conjunction with offset reflectors to remove blockage effects. In the design of complex multielement feed arrays for offset reflectors, the element excitations are usually synthesized using the isolated element properties. Proper performance of the array often requires that these theoretical excitations be modified to account for the effects on the feed elements due to the array environment. Near-field planar probing of the fields of the feed array have been found to provide an efficient and accurate method of predicting the secondary performances, including cross polarization and axial ratio. The nearfield measurement technique, moreover, provides an extremely effective method of determining the element performance and for determining the required compensation for desired antenna performance.     

Analytical array polynomial method for linear antenna arrays with phase-only control

A new analytical synthesis technique is developed for the phase-only control of linear antenna arrays and is based on the Schelkunoff's unit circle. The array factor is formulated as an array polynomial in the complex z-plane and as a product of corresponding subpolynomials such that their roots are located on the unit circle. A constraint is derived such that the expansion of the subpolynomials yields current excitations with unity magnitudes. In general, the constraint of phase-only control forces some element excitations to be zero for an arbitrary number of array elements. The subpolynomial with the largest degree is used to synthesize the main beam characteristics. The null steering for interference suppression is obtained by using only one subpolynomial to steer only one null. The results verify the developed analytical solution to synthesize the prescribed patterns using the phase shifters of the linear antenna arrays.     

Rapid method for obtaining footprint patterns for very large antenna arrays

A new antenna pattern synthesis technique that allows the design of large planar antenna array radiating footprint patterns of a specified boundary with controlled ripple and sidelobe levels is presented. The method synthesises the desired footprint as a composition of a set of circular Taylor patterns appropriately weighted with the samples of the pattern obtained after stretching or shrinking a continuous circular aperture distribution developed by the Elliott-Stern method. A footprint of continental Europe radiated by a planar array with a large number of elements shows the technique's performance. The synthesis procedures were completed in about 1 s using a desktop computer.     

Hybrid Amplitude Control Antenna Array System for Energy Efficient W-CDMA Network with Adaptive Coverage and Capacity

This paper introduces a novel technique and mathematical formulation of two dimensional elastic footprint variations and adaptive sector configuration variations by using a hybrid adaptive amplitude control antenna array system. The antenna array system can control the elevation beam-widths from 6.84° to 13° and the azimuth beam-widths from 33° to 93° for obtaining the adaptive capacity and coverage. The work illustrates the application of the antenna array system in the energy efficient W-CDMA network. The antenna array half-power beam width variation is achieved by using the antenna array amplitude control and co-located multiple antenna array switching. The Node-Bs can adaptively switch to three, four, five, six and non uniform sector configurations with the antenna array beam width control and adaptive neighbor relations. Sector configurations will vary according to the pre-defined specific traffic loading percentages out of Node-B’s total channel capacity to reduce the energy consumption of the entire network. The paper introduces an adaptive footprint overlaps shifting technique, where the sector with less traffic load will expand its footprint towards the sector with higher traffic load and the sector with higher traffic load will shrink its footprint by maintaining a fixed footprint overlaps to improve the coverage and the capacity of the network. The footprints overlap shifting is applicable only for the active sector antennas facing each other. The results confirm that the proposed antenna array system outperforms the automatic tilt optimization and can control coverage, capacity and improve the energy efficiency of the W-CDMA network.     

Element Failure Correction for a Large Monopulse Phased Array Antenna With Active Amplitude Weighting

Recently a new method is introduced to synthesize low sidelobe patterns for planar array antennas with a periodic element arrangement. The method makes use of the property that for a planar array with periodic spacing of the elements, an inverse Fourier transform relationship exists between the array factor and the element excitations. This property is used in an iterative way to derive the array element excitations from the prescribed array factor. The same method is also able to partially compensate the degradation of the sidelobe and gain performance of array patterns due to element failures. Numerical examples of array-failure correction using this method are given for ultralow sidelobe sum and difference patterns of a 5800-element circular array where the failed elements are randomly dispersed across the aperture. The tapers in this array are created exclusively by active weighting in the transmit/receive (T/R) modules using variable gain control.     

基于迭代FFT算法的平面稀疏阵列优化方法

提出了一种基于迭代FFT算法的优化方法来实现平面稀疏阵列的峰值旁瓣电平优化,并给出了详细的优化步骤.在给定的旁瓣约束条件下,利用阵列因子与阵元激励之间存在的傅里叶变换关系,对不同的初始随机阵元激励分别进行迭代循环,就可以降低稀疏阵列的旁瓣电平.在迭代过程中,根据稀疏率将阵元激励按幅度大小置1置0来完成阵列稀疏.仿真实验...     

Eigen-approach for wide-band interference suppression

This paper presents a new synthesis technique of an antenna array pattern for multiple wide-band interference suppression. The proposed technique uses an eigen-approach to design an array pattern with arbitrary controlled multiple broad suppressed sectors by controlling the array complex element excitations. The eigen-approach determines the element complex current ratios that produce the closest perturbed pattern in the least squares sense. Numerical results show that the proposed technique can suppress multiple wide sectors in the array pattern and control the sector depths by applying an appropriate weight factor on the mean square error of the perturbed pattern in the prescribed sector intervals.     

Design of dipole arrays with equal element impedances

A simple method for synthesising a given radiation pattern from a new type of dipole array, an unequal element array, is described. The input impedances of the elements are the same and the lengths and the radii of the dipoles are different.<>     

Least squares pattern synthesis for conformal arrays

The problem of synthesising low sidelobe beams from conformal arrays consisting of few elements and large radius of curvature is addressed. Experimental results are presented for a 12 element array of linearly polarised elements forming a faceted array with radius of curvature 1.5 m. It is shown that by calculation of an aperture correcting matrix, sidelobe levels of 40 dB can be obtained from the array by application of conventional linear array Taylor weights. Beam steering is achieved by aperture phase tapering while low sidelobe levels are maintained     

Phased arrays based on oscillators coupled on triangular and hexagonal lattices

Phased arrays have been proposed in which a two-dimensional array of voltage-controlled oscillators coupled to nearest neighbors provides excitations for the radiating elements which are properly phased to result in a steerable radiated beam. These arrays have been arranged on a rectangular lattice and the beam is steered by tuning the oscillators along the four edges of the array. Proposed here are similar arrays in which the oscillators are coupled on a triangular lattice or a hexagonal lattice and provide excitations for radiating elements similarly disposed in a planar triangular array. Beam steering is accomplished by tuning the oscillators along the three edges of the array. The dynamic behavior of the arrays is studied via a continuum model and the results compared with those of a full nonlinear discrete analysis and a linearized discrete model.     

Out-of-Band Response of Antenna Arrays

The response of antenna arrays to out-of-band frequencies has been analyzed using the effective-aperture approach. An average value of effective aperture can be obtained by averaging the incidence angle and the polarization of the incidence field. Far-field patterns have also been calculated by treating the array element excitations as random variables. The randomness in the element excitations causes a decrease in directivity and an increase in sidelobe level. Out-of-band measurements on a slotted-waveguide array confirm these trends.     

Design of efficient, easily feed-matched array antennas by jointoptimisation of excitations and element geometry: pencil beam example

By using simulated annealing for simultaneous optimisation of the geometries and excitations of the array elements, it is often possible to design array antennas that generate specified radiation power patterns, have elements with real active impedances, and are easily feed-matched. The example of a twelve-element pencil beam antenna fed by coaxial cables of practical dimensions with no additional circuitry is described     

Pattern synthesis of array antennas with additional isolation ofnear field arbitrary objects

A new technique for synthesising array antennas in the presence of arbitrary obstacles in the near field region is presented. This technique allows a prescribed far field pattern to be synthesised, while trying to avoid coupling with near field obstacles through the constraint of minimising the radiated power over the obstacle surface. Some results have been obtained showing that the obstacles are finally isolated from the array antenna radiation     

Source synthesis for training array neural networks

The authors introduce techniques for synthesising realistic multiple source antenna `measurements' from single source measurements and for recalibrating single source baseline measurements after subsequent array failure. Synthesised data are compared with measured data and used to train a neural network to perform direction finding     

An efficient neural network algorithm for reflector surface errorcompensation

A neural network algorithm for electromagnetic compensation of reflector surface error effects is formulated. Sets of trained neural networks are used to compute the compensation excitations for array feeds. The networks were trained using data generated with the constrained least squares (CLS) compensation method. Once trained, the calculation of the excitations is accomplished in significantly less time than required by the original constrained least squares algorithm. The surface error profile for a distorted reflector antenna is expanded using bivariate surface basis functions. Each of the trained networks corresponds to one of the expansion functions. Excitations computed using the neural networks are superposed to produce composite compensation excitations for the distorted reflector. The compensation results for a distorted reflector are presented, and the neural network algorithm performance is compared to the original CLS technique     

Maximisation of signal/noise ratio in array with broadened zero

A technique for synthesising a maximally-flat zero in antenna array while maximising the signal/noise ratio is described. It is shown that the optimum radiation pattern consists of a main beam, a cancellation beam and its pattern derivatives. The properties and characteristics of the pattern are also discussed.     

Iterative least-squares synthesis methods for conformal arrayantennas with optimized polarization and frequency properties

An iterative least-squares synthesis technique is presented for the optimization of the element excitation in conformal array antennas. This method allows the designer to have predefined goals for the shaped radiation pattern over a selected frequency band and for the polarization properties of the array. Linear or circular polarization can be used in the synthesis. Different kinds of synthesis goals can be set, whereby the copolarization or cross-polarization properties of the array are weighted or a narrowband or wideband design is sought. The amplitudes of the element excitations can be fixed. Several synthesis examples are presented for an array on a sphere with circular polarized elements. Broad-band and low cross-polarization designs are included