Optimum quantised low sidelobe phase tapers for arrays

A genetic algorithm is used to find optimum quantised low sidelobe phase tapers for linear arrays of point sources. This method has the advantage that the optimum taper is found in quantised phase space rather than in continuous phase space     

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.     

Mutual coupling and element efficiency for infinite linear arrays

A formulation is presented of the interrelationship among mutual coupling element efficiency, active impedance, and element radiation patterns for infinite linear (uniformly spaced) arrays. Numerical results are obtained for element efficiency and mutual coupling when the array elements are elementary dipoles. A new lower upper bonnd is obtained on element efficiency. This upper bound is expressed directly in terms of the element patterns in the open-circuit array environment.     

Cross-polarization and sidelobe suppression in dual linearpolarization antenna arrays

In recent years, there has been an increasing interest in dual linear polarization antennas for various purposes, e.g. polarimetric synthetic aperture radar (SAR) imaging. A key design goal for dual polarization antennas is to obtain a high cross-polarization suppression. When using standard techniques for improving the cross-polarization suppression in dual linear polarization antenna arrays undesired sidelobes appear. This paper describes the properties of some known cross-polarization suppression methods and presents a new method for obtaining high cross-polarization suppression and simultaneously avoiding undesired sidelobes     

A novel linear and planar multiband fractal-shaped antenna arrays with low sidelobes

Fractal antenna arrays are usually used to tune multiband frequencies. However, these types of iteratively constructed antennas are associated with undesirable high sidelobe levels and low directivities. In this paper, an optimization procedure based on the genetic algorithm is used to find the optimal weights of the array elements such that the corresponding array patterns have low sidelobe levels and good directivity. Moreover, the fractal nature in the proposed arrays is maintained regardless of the optimized weights. Thus, the proposed fractal-shaped array maintains its capability in performing multiband frequency operation. These good radiation features make the proposed fractal-shaped array more appropriate for the current and future wireless communication applications. Simulation results confirm the superiority of the presented linear and planar fractal-shaped array structures with compared to the conventional fractal cantor linear array and the standard Sierpinski carpet planar array. For the proposed fractal cantor linear array, the sidelobe level has been reduced to more than −20 dB at different operating frequencies, and the directivity has been improved by more than 8 dB, while the modified Sierpinski carpet planar array has achieved −30 dB depressions in the sidelobe level and 6 dB improvement in the directivity.     

The design of antenna arrays with tapered sidelobe heights

Arrays for many radar and sonar applications have customarily been designed for equal sidelobe levels. This is, perhaps, as much due to the convenience of the analytical Dolph-Chebyshev technique as to any specific requirement. Using a simple adaptation of a previously reported numerical technique for symmetrical arrays, designs can be obtained whose directional response has a specified taper on the envelope containing the sidelobes. The method is applicable to both sum and difference patterns for both line and planar arrays. However, there seems to be little to be gained by this procedure except in the case when the outer sideiobes are to be more severely controlled.     

Mutual coupling compensation of linear antenna array using evolutionary optimization technique

This paper presents an optimization-based approach to compensate for the mutual coupling effect and to reduce the sidelobe level (SLL) of the normalized radiation pattern by optimizing the current excitation amplitude of the antenna array elements. Due to the mutual coupling effect, the SLL of the radiation pattern is increased, and thereby, the field pattern of the antenna array is severely degraded. This causes interference with other communication systems working at the same frequency. Toward the compensation of the mutual coupling effect and reduction of SLL, the Cat swarm optimization (CSO) algorithm is employed, and the excitation amplitudes of the antenna elements are optimized. In this regard, optimizing the cost function is defined by introducing the impedance factor (IF), calculated by using the self-impedance and mutual impedance of the antenna elements. The proposed method for the synthesis of a mutually coupled linear antenna array is less expensive, simpler to use, and more effective. Array sets of 4, 6, 8, and 10 elements are considered for optimization.     

Optimum scannable planar arrays with an invariant sidelobe level

This paper presents two alternative methods for determining the current distribution in the elements of a scanning rectangular array which is optimum in the sense that its radiation pattern has a constant sidelobe level and a narrowest beamwidth in all directions. Exact formulas for both even and odd numbers of elements are given. The dependence of the main-lobe beamwidth on the total number of elements, the element spacing, the sidelobe level, and the scan angle is studied in detail. The minimum required number of controlled elements in a square array with electronic beam scanning over a specified sector for a guaranteed upper limit on beamwidth without grating lobes is determined. Numerical results are included, which illustrate many interesting features of the new design technique.     

Directions of arrival estimation with planar antenna arrays in the presence of mutual coupling

Directions of arrival (DoAs) estimation of multiple sources using an antenna array is a challenging topic in wireless communication. The DoAs estimation accuracy depends not only on the selected technique and algorithm, but also on the geometrical configuration of the antenna array used during the estimation. In this article the robustness of common planar antenna arrays against unaccounted mutual coupling is examined and their DoAs estimation capabilities are compared and analysed through computer simulations using the well-known MUltiple SIgnal Classification (MUSIC) algorithm. Our analysis is based on an electromagnetic concept to calculate an approximation of the impedance matrices that define the mutual coupling matrix (MCM). Furthermore, a CRB analysis is presented and used as an asymptotic performance benchmark of the studied antenna arrays. The impact of the studied antenna arrays geometry on the MCM structure is also investigated. Simulation results show that the UCCA has more robustness against unaccounted mutual coupling and performs better results than both UCA and URA geometries. The performed simulations confirm also that, although the UCCA achieves better performance under complicated scenarios, the URA shows better asymptotic (CRB) behaviour which promises more accuracy on DoAs estimation.     

A new quasi-Yagi antenna for planar active antenna arrays

In this paper, a novel broadband planar antenna based on the classic Yagi-Uda dipole antenna is presented, and its usefulness as an array antenna is explored. This “quasi-Yagi” antenna is realized on a high dielectric-constant substrate, and is completely compatible with microstrip circuitry and solid-state devices. This antenna achieves a measured 48% frequency bandwidth for voltage standing-wave ratio <2, better than a 12-dB front-to-back ratio, smaller than -15 dB cross polarization, and 3-5-dBi absolute gain. Mutual coupling of the antenna in an array environment is investigated. Finally, three simple arrays are presented, demonstrating the usefulness of the antenna as an array element. This novel antenna should find wide application in wireless communication systems, power combining, phased arrays, and active arrays, as well as millimeter-wave imaging arrays     

Synthesis of linear antenna arrays

Synthesis of antenna arrays employing theL_{2}-norm as well as theL_{infty}-norm is discussed. The approximation in theL_{infty}-norm is obtained making use of Lawson's algorithm. A general iterative perturbation technique has been evolved for pattern synthesis for the case when the antenna currents alone are varied as web as for the case when both the antenna currents and the element positions are simultaneously varied. A few illustrative examples are given. The convergence of the iteration and the uniqueness of the solution are discussed.     

Nonuniformly spaced linear and planar array antennas for sidelobe reduction

The material discussed can be divided into two parts. In the first part, an iteration method is presented for calculating the distances between the elements of a symmetrical nonuniformly spaced linear array antenna for sidelobe reduction. The amplitude of the excitation is assumed to be constant. The iteration method is applied to linear array consisting of 24 elements. After a few iterations, the sidelobe-to-mainlobe power ratio was reduced to over 22 dB from its value of 13.2 dB for uniform array spacing. In the second part, several symmetrical nonuniformly spaced planar array antennas have been designed, using the nonuniform linear array spacings of part one. The planar arrays include square-shaped and circular structures, with the number of elements ranging from 284 to 576. The iteration method discussed can be applied to linear arrays with any number of elements to obtain nonuniform grid spacings for sidelobe reduction. A number of planar grid structures can be constructed using the nonuniform linear grids. The nonuniform linear and planar arrays utilize fewer radiating elements and result in desirable sidelobe structures.     

一维线阵唯相位低副瓣技术分析

实现了基于最速下降方法(SDM)的唯相位低副瓣技术,提出了SDM方法的步长公式,对不同阵元分析了唯相位技术的低副瓣性能和能量效率水平,总结了最高副瓣电平同阵元数目的关系,分析了幅相加权对于最高副瓣电平和能量效率水平的影响。     

Evaluation of directivity for planar antenna arrays

In this paper, the directivity, including phase shift factors, for several types of uniformly excited planar arrays is obtained. Four types of dipole arrays are considered: arrays of collinear short dipoles, and of parallel short dipoles; and broadside and end-fire arrays of crosses of short dipoles. Curves of directivity versus inter-element spacing and scan angle for planar arrays with these element power patterns are presented     

Effects of coupling accumulation in antenna arrays

Mutual coupling between antenna elements in a phased array causes array performance to vary with scan angle. Large impedance mismatch and radiation loss can occur in certain critical directions for which the steering phase advances match the antenna coupling delays. At these critical scan angles, many coupling contributions add inphase to produce a large impedance mismatch and minimum radiation from the array. Several different phased arrays have exhibited scanning "blind" regions that appear to be a consequence of coupling accumulation. A large, flat, homogeneous antenna array is analyzed, and a relationship is found between the critical scan angles and phase of the mutual coupling coefficients. Extensive measurements on arrays of horn antennas have shown radiation minima that correlate with coupling phase measurements and with theory.     

Investigation on antenna coupling in pulsed arrays

Pulsed arrays are becoming popular in new ultrawide-band applications to achieve long-range coverage, high capacity and to identify the angle of arrival of multiple echoes in complex environments. As in the monochromatic regime, distortion of ultrawide-band transmitted and received signals can result from the coupling between individual radiators that are in close proximity. This paper investigates the time-domain coupling in finite arrays that radiate short pulses, by introducing the concept of time-domain "active" array factor and "active" element factor. The proposed model highlights the signal-distortion phenomenology and obtains useful guidelines to reduce pulse coupling, even in dense arrays, by a proper choice of the geometrical and electrical parameters.     

一种空气同轴馈电的X波段低副瓣阵列天线

设计了一种应用于雷达系统中的低成本低副瓣阵列天线, 该天线阵包含256个辐射单元, 由四个64单元的子阵组成, 采用波导合成网络进行功率合成.天线单元采用空气同轴馈电的角锥喇叭, 空气同轴馈线内外导体呈方型结构, 其终端为短路馈电方式, 实现了内导体的自支撑设计和较低的传输损耗, 并依据综合幅度分布采用若干数量的不等功分器进行低副瓣设计.测试结果表明, 小于2的驻波带宽为0.5 GHz, 相对带宽为7.5%.另外, 中心频率的增益为30 dB, 增益大于29.5 dB的带宽为0.2 GHz, E面和H面的旁瓣电平为28.5 dB和29 dB.     

Phase-only synthesis of minimum peak sidelobe patterns for linearand planar arrays

Minimization of the maximum sidelobe level for a given array geometry by phase-only adjustment of the element excitations is considered. Optimum phases are obtained by using a numerical search procedure to minimize the expression for the pattern sidelobe level with respect to the element phases. Results for both linear and planar arrays of equispaced elements are presented. The data suggests that optimum sidelobe level is a logarithmic function of array size, and optimum patterns have relative efficiencies that are typically somewhat greater than for comparable-amplitude tapered arrays. An analytic synthesis algorithm is presented for use on very large arrays for which the numerical search technique for the minimization of the sidelobe level is computationally impractical. This method produces patterns with characteristics similar to arrays synthesized using the numerical search method, i.e. relatively uniform angular distribution of energy in the sidelobe region, and generally decreasing maximum sidelobe level as the array size is increased     

Evolutionary optimization for pattern synthesis and reduction of mutual coupling of linear antenna arrays

Optimal design of antenna arrays to minimize the mutual coupling effects in the geometrical arrangements of the linear antenna array (LAA) and circular antenna array (CAA) is dealt with in this work. Two different cases are considered to reduce the effect of LAA and CAA: Case‐1 in which the current excitations of the antenna array are considered to get the optimal radiation pattern of two geometry called LAA and CAA and Case‐2 in which inter‐element spacing and current excitations are both optimized for LAA geometry. A cost function that involves the mutual coupling factor as an optimization factor is developed to reduce the side lobe level (SLL), which takes mutual coupling effects into consideration. Excitation values and inter‐elemental spacing are optimized using particle swarm optimization (PSO). In LAA, for 8‐, 12‐, 16‐element arrays, SLLs are reduced by ?15.52, ?16.71, and ?17.78 dB in Case‐1. For the same sets of element arrays, SLLs were reduced by ?17.35, ?19.71, and ?20.26 dB in Case‐2. In CAA, the current excitations of the antenna array are optimized. For 8‐, 12‐, and 16‐ element arrays, SLLs are reduced to ?7.405, ?10.52, and ?9.43 dB, respectively. The arrays coded with the help of MATLAB based computation and the results obtained by MATLAB are validated by using CST.