Fast Iterative Method of Power Synthesis for Antenna Arrays

A fast and simple method of power synthesis for antenna arrays of arbitrary geometry is presented. The method adopts an auxiliary function having the desired amplitude pattern and a generic phase pattern, and determines in closed form the array pattern approximating the auxiliary function in both amplitude and phase. A cost function involving the auxiliary function and the approximating pattern is minimized by modifying the phase pattern of the auxiliary function, using a simple and fast iterative technique. Once the optimal phase pattern has been found, the array pattern approximating the corresponding auxiliary function is the synthesized pattern. The proposed method allows to satisfy stringent requirements on the amplitude pattern, including multibeam synthesis and radiation suppression within large angular regions. Numerical results show the effectiveness of the algorithm and are compared to those obtained using other existing methods. In order to achieve a more significant comparison such methods have been properly modified to improve their performances. Such comparison shows that the presented algorithm allows a significant reduction of CPU time with respect to the other considered methods, as well as a weaker dependence on the starting point. Finally, the presented method is extended in such a way as to reduce the dynamic range ratio (DRR) of the array excitations.      

Constrained beam scanning for linear arrays of antennas

A method to scan the radiation pattern of a linear array, simultaneously reducing the pattern amplitude in constant directions, is described. The scanning process is obtained by phase control of the array excitations and, if necessary, by amplitude perturbations not exceeding a small threshold.     

一种基于遗传算法的唯相位宽零陷波束赋形方法

传统阵列方向图宽零陷形成技术需要对阵元施加复加权或者阵元位置扰动等复杂操作,实际实现比较困难。提出了一种基于遗传算法的唯相位波束赋形方法,针对宽零陷特点,结合均匀线阵方向图数学模型,设计一种适应度函数,优化阵元相位扰动值,最终获得符合要求的宽零陷阵列方向图。仿真结果表明,该方法可以在唯相位条件下形成较深的宽零陷,且零陷较平坦,收敛速度较快,稳健性较好。     

Transmit patterns for active linear arrays with peak amplitude andradiated voltage distribution constraints

Distribution functions used in array antenna design typically synthesize specified pattern characteristics without consideration for either the peak amplitude of the radiating elements or the aperture radiated power. There do exist applications, however, in which the pattern synthesis must employ such constraints. In the transmit mode of active array antennas, for example, it is desirable to radiate as much power as possible subject to a per-element peak amplitude constraint while simultaneously suppressing the outer sidelobes. This paper discusses the design considerations of the constrained least squares (CLS) distribution function. In the CLS distribution, most of the radiating elements near the array center are set to their maximum value while only a few of the outer elements are tapered. A method for generating CLS distributions given constraints on both the peak element amplitude and the total effective radiated voltage (ERV) is discussed. The design involves specifying the desired ERV and a weighting function that allows selectively suppressing sidelobes in specified regions. The effects of these design parameters on the far-field patterns are explored     

耦合激励系数及对称振子阵列天线的有源方向图研究

为了深入探讨相控阵天线单元间的耦合对阵中单元方向图的影响,以阵列天线单元S参数为基础,给出了阵列天线单元的耦合激励系数计算公式,利用阵列天线单元间的耦合激励系数分析计算阵中单元的有源辐射方向图.同时利用矩量法分析由偶极子单元组成的阵列,并把阵列中每个单元的感应电流幅度和相位与耦合激励系数的幅度和相位进行比较,二者数据基本一致.矩量法计算的单元有源方向图与本文提出方法的计算结果吻合良好,验证了本文给出的阵列耦合激励系数及阵列天线阵中单元有源方向图计算方法的可靠性.     

相频扫描阵列通道幅相测试方法研究北大核心CSCD

相频扫描阵列具有频扫低成本和相扫控制灵活等优点,被广泛用于军事和民事。该类阵列的增益、相位扫描面波束副瓣等受通道的幅度相位一致性影响较大,需要经过校准补偿以获得高性能波束。准确高效的通道幅相测试方法是进行校准的前提和基础。文中首先分析了组成相频扫描阵列的波导缝隙天线近场区域的辐射特性,得出在柱面波区域进行取样的可行性。在此基础上提出了扫描架逐行移动取样以及中场取样两类共五种测试方法,并给出了程差的幅相补偿方法。计算了各测试方法所引入的系统误差,分析了它们各自的适用场合。最后对比其中两种测试方法在某相频扫描阵列样机中的幅相测试结果,并给出了补偿校准后的波束测试结果,验证了文中所提出测试方法的准确性和有效性。     

Method of the Amplitude–Phase Synthesis of a Pareto-Optimal Planar Antenna Array

A method of the amplitude–phase multicriteria synthesis of a Pareto-optimal antenna array is proposed. The method is based on representation of the initial antenna array synthesis problem in the form of successively solved partial problems (subproblems) with small dimensionality. Each subproblem is reduced to determination of Pareto-optimal parameters of the amplitude–phase distribution of an additional beam added to the initial radiation pattern.     

基于LMS算法的功率放大器控制系统

高频表面波雷达对发射功率要求很高,通常会采取功率空间合成的办法使数个较小功率的发射机合成一个较大的合成发射功率。首先介绍了子天线输入信号的幅相不一致对阵方向图产生的影响,然后讨论了不同的自适应算法的优缺点,选定了一种合适的算法并给出了硬件框图。选定的自适应控制算法具有较好的收敛性和稳态失调性,计算量小,实现简单,通过单片机及其外围模数、数模转换电路能够很方便的实现功放的幅相校准系统,使功放的输出信号的相位、幅度满足要求。     

一种微波脉冲大功率器件的幅相测试方法

宽带固态有源相控阵雷达对发射通道幅相特性有严格的一致性要求，本文就此进行了简单地论述，提出了一种微波脉冲功率器件的幅相特性测试方法，并给出了试验数据。     

Three-dimensional electromagnetic power deposition in tumors usinginterstitial antenna arrays

Interstitial arrays of insulated antennas have shown promise for microwave hyperthermia treatment of deep-seated tumors. Available analytical techniques for predicting the electromagnetic (EM) power deposition of these antennas have been limited to the case of a homogeneous conductive medium surrounding the array. Since tumors and host tissue may differ in their electrical characteristics, it is necessary to consider the impact of this variation in electrical properties and the geometry of the tumor in the calculation of the EM field distribution and power deposition pattern when modeling interstitial antennas. In this paper a three-dimensional model of a tumor of arbitrary shape subjected to the fields of an interstitial antenna array is developed to predict the EM power deposition in an inhomogeneous tumor-tissue medium. The volume integral equation for the imbedded tumor is developed and solved by method of moments. The incident fields are calculated based on the available formulation of interstitial antennas in homogeneous media. The accuracy of the developed computer code was checked by comparing the results from the volume integral approach with the Mie solution for the special case of spherical tumors. Good comparison was obtained for tumors with properties approximately 25 percent different from those of the surrounding tissue. Comparisons of results from models of antenna arrays with and without imbedded tumors show significant differences in their predictions of the EM power deposition in the tumor. Hyperthermia protocols generally specify uniform temperature distribution within the tumor. The developed inhomogeneous model was used to examine the feasibility of controlling the uniformity of the power deposition pattern in large tumors by adjusting the amplitude or relative phase between the array elements. Results are presented to show that a phase lead of +90 degrees or relative amplitude of 4.0 on one antenna in a square array of four antennas could be used to shift the power deposition pattern to sequentially heat outer portions of a 2 cm diameter tumor, thereby achieving a more uniform time-averaged temperature distribution in the tumor.     

幅相误差对均匀圆阵列系统性能的影响

幅相误差是制约天线阵系统性能的一个重要因素。本文通过建立存在随机幅相误差时的均匀圆阵列模型,分析了此时均匀圆阵列场方向图函数和功率方向图函数的统计特性;围绕方向性系数、旁瓣电平和半功率波瓣宽度三个系统指标,计算了随机幅相误差对均匀圆阵列系统性能的影响;最后在数值分析的基础上进行了计算机仿真和验证。     

A frequency-controlled beam-steering array with mixing frequency compensation for multichannel applications

A frequency-controlled beam-steering planar array with mixing frequency compensation is presented for cost-effective multichannel phased array applications. The new feed networks for frequency compensation not only operate in wide band but also ensure radio-frequency (RF) amplitude imbalance cancellation and progressive phase distribution. The parallel equal power dividers installed in both LO and intermediate-frequency (IF) feed networks provide uniform amplitude and phase distribution, while the fixed delay lines installed in the LO feed network exhibit precise phase progression, compared to a series feed structure. The LO power imbalance caused by the unequal delay line loss between elements is corrected by pumping each mixer into the LO saturation region, leading to linear IF-RF response. Thus, sidelobe degradation and pattern distortion caused by the RF amplitude imbalance, as well as the beam-steering error and beam squint caused by the phase errors of the delay lines, are removed. The proposed feed networks combined with quasi-Yagi antenna arrays and microwave monolithic integrated circuit mixers realize a broad bandwidth of more than 3 GHz in K band for multichannel wireless applications. The K band transmitter/receiver pair proposed in this paper successfully demonstrates two-channel simultaneous RF transmission and single channel 50-Mb/s data communication with 40/spl deg/ scanning. This simple, compact, yet cost-effective planar array ensures multichannel broadband wireless communications with beam-steering capability.     

An investigation of concentric ring antennas with low sidelobes

An analysis is made of circular antenna arrays with diameters being 2 to9lambda(the minimum inner circle diameter being0.4lambda) containing 3 to 18 concentric circles. For the purpose of computation of the array factor the elements of the array are assumed to be isotropic radiators. The elements of each circle have equal current amplitudes and are phased so that the contributions of all the elements add in phase in the direction of the main beam. The Chebyshev radiation pattern function is approximated by a truncated Fourier-Bessel series, from which the current amplitude of each circle is obtained. From these current amplitudes a method for computing the current amplitude to excite a new distribution of fewer circles is shown. Also, an empirical method is given for improving the sidelobe level of the radiation pattern by adding an element to the center of the array. A number of circles in the array sufficient to avoid pattern deterioration is found to be the integer nearest to5d/4lambdafor -20 and -30 dB sidelobe level and4d/3lambdafor -40 dB, wheredis the diameter of the array. This represents a large reduction in the number of circles needed over the Fourier-Bessel series representation in the case of large antennas. Experimental verification of the computed pattern is made for an array of two concentric circles with diameters of0.8lambdaand1.6at a frequency of 90 Mc/s. The elements of the array were vertical monopoles.     

Random removal of radiators from large linear arrays

The effects on the radiation pattern whenNpairs of symmetrically located radiators are removed at random from a large(2N_{0}+1)-element linear array are studied as a statistical problem. It has been possible to determine the limiting bounds of the radiation pattern the probability that the main-lobe beamwidth is not widened by more than a given percentage, the probability that a certain sidelobe does not deteriorate by a specified amount and the probability that all sidelobes are below a specified level. The general analysis is valid for arrays with an arbitrary amplitude distribution which is symmetrical with respect to the center element and with an arbitrary progressive phase shift. Curves showing computed statistical data for a 201-element array with both the uniform and a cosine-squared amplitude distribution are presented.     

Optimization of SAR distributions in liver and lung regionsirradiated by the H-horn annular phased array hyperthermiasystem

The author discusses a type of annular phased array (APA) system-the H-horn APA. The phase and amplitude control of power deposition patterns for this system have been theoretically analyzed at a frequency of 200 MHz. The formulas for calculating the electric field (E-field) and specific absorption rate (SAR) for this APA system have been derived and can be applied to other types of APA systems. Models on computerized tomography (CT) scans from liver and lung regions have been used for predicting optimization of the E-field and SAR patterns in the case of the relative phase and amplitude changes. It is shown that the phase and amplitude control of SAR patterns results in a more selective and effective heating of tumors situated eccentrically and deeply within the body. The numerical results indicate that it is possible to shift the absorbed power patterns by electrically varying the phase and/or the amplitude of the sources and manually moving the positions of the horns     

Circularly symmetric RF commutator for cylindrical phased arrays

A new feed concept is described which greatly simplifies the problem of commutating the RF distribution system of a cylindrical phased array. The feed consists of a circular parallel-plate radial transmission line with a central set of probes and a ring of peripheral probes. The array of probes in the center can be phased to produce an amplitude distribution in the parallel-plate line in any given direction. Proper setting of only two phase shifters connected to the central probes can cause any sector of the peripheral probes to be excited with the proper amplitude distribution necessary to produce a directive pattern with low sidelobes as well as a monopulse difference pattern when the peripheral probes are connected, through collimating phase shifters, to the active radiating elements of a cylindrical array. The cylindrical array can be scanned through360degin fine increments by continued indexing of the amplitude distribution generated by the central probes. ExperimentalLband hardware, built to prove the feed technique, is described. Nine central probes in a 0.25-inch thick 21-in diameter model produced a cardioid distribution and an orthogonal figure-eight distribution which could be commutated together by adjustment of two phase shifters. Measured insertion loss between the central probes and 48 peripheral probes showed only 0.1-dB loss over a 6-percent band. Coupling measurements between the three available central terminals indicated isolation between the various ports of 23-35 dB. The minimum insertion loss and the corresponding transmission phase between the central feed and the peripheral probes was shown to be independent of the setting of the two control phase shifters which were set to have conjugate phase shift.     

Quasi-optical 150-GHz power combining oscillator

A quasi-optical power combiner for a five-element in-line oscillator array is experimentally investigated at 150 GHz. The combiner consists of a periodic dielectric phase grating (hologram) which transforms the near-field of a rectangular horn antenna array into a pseudo-plane wave. The horn array is excited by IMPATT oscillators operating uniformly in both amplitude and phase. A dual offset reflector set-up transforms the pseudo-plane wave to a Gaussian beam which matches the field pattern of a dual mode receiving antenna. Even though an inter-element spacing of 9.5 /spl lambda/ has been chosen, the passive structure gives a power combining efficiency of 74.1%. The power combining oscillator has been operated in both free-running and injection-locked mode. A CW output power of 78.0 mW and 83.5 mW was measured for the free-running and injection-locked oscillator, respectively, which is corresponding to a power combining efficiency of 66.5% and 71.2%, respectively.     

近场测量相控阵天线的全息成像方法

研究了一种利用近场测量技术全息成像相控阵天线口径幅相的方法。该方法是把近场测量获得的方向图函数与由单元形式及幅相分布表示的方向图函数进行比较,采用FFT算法和空间域的Fourier重构法,可以快速、精确地成像出相控阵天线口径的“全息图”,进而诊断出阵中单元幅相的奇异程度。通过仿真实验,检验了该方法的成像分辨率和精度,并考察了不同口径区域的成像误差对辐射方向图的影响程度,说明该具有非常好的应用前景。     

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     

Reconfigurability and Beam Scanning With Phase-Only Control for Antenna Arrays

A new method is presented on constrained power synthesis for reconfigurable arrays of arbitrary geometry. Given a number of suitable masks, the algorithm yields excitation vectors whose array patterns belong to such masks, and for each array element the excitation amplitude holds constant during the pattern reconfiguration, so as to ensure phase-only control. Each excitation amplitude is optimized, and the method allows to control the dynamic range ratio (DRR) of the excitations. The solution to the synthesis problem is found as a point of the intersection between two suitable sets, by using the method of successive projections. The proposed method can also be used to solve problems of constrained beam scanning. To this aim it is sufficient to select a high number of masks, close to each other in the angular sector of interest and shaped in such a way as to reproduce the desired scanning beam. The algorithm yields array patterns belonging to these masks, thus performing a discrete scanning by phase-only control, and allows to control the DRR. Several numerical examples show the effectiveness and the capabilities of the method.