SAR CHARACTERIZATION OF FOCUSED PLANAR ARRAY OF WATER-LOADED MODIFIED BOX-HORNS FOR HYPERTHERMIA

A 4×4 planar array of modified box-horns as a microwave hyperthermia applicator is theoretically studied to characterize power deposition (SAR) in heating tissue (muscle) at 2450 MHz. A modified box-horn is a novel improved version of conventional box-horn in which horn exciting the box waveguide is flared in both E-and H-planes. Modified box-horn supports TE₁₀ and TE₃₀ modes. The amplitude distribution over the H-plane of the box-horn aperture is a closer approximation to the uniform distribution. It is proposed that the interior of the box-horn be filled with water to provide a better impedance match to biological tissue. By applying Fresnel-Kirchhoff scalar diffraction field theory, the expression for electric field in heating region is derived and distribution of specific absorption rate (SAR) in that region due to planar array of modified box-horns as direct contact applicator is evaluated at 2450 MHz. The results of modified box-horn array are compared with those of a single modified box-horn operating at the same frequency. Results demonstrate that planar array of modified box-horns offers improvement in SAR distribution and penetration depth. It is shown that by changing the phase and amplitude of excitation of the modified box-horns of the array, the relative amplitude and position of the hot spot can be changed. The present analysis is validated through the results obtained by plane wave spectral technique.     

Analysis of the SAR distributions in three-layered bio-media in direct contact with a water-loaded modified box-horn applicator

This paper presents theoretical analysis of the specific absorption rate (SAR) distribution in three-layered bio-media (skin, fat, and muscle layers) in direct contact with a modified box-horn applicator in which the horn is flared in both the E- and H-planes for hyperthermia treatment of cancer. The modified box-horn is assumed to be filled with water to provide a better impedance match to the bio-media. The present analysis is based on a plane-wave spectral technique. The spatial distribution of SAR in skin, fat, and muscle layers are computed and presented at 433 and 2450 MHz. Higher SAR value in each of the bio-layers, higher penetration depth, and lower resolution in the muscle layer are observed at 433 MHz in comparison to those at 2450 MHz for the water-loaded modified box-horn. The effect of substituting a pyramidal horn in place of an H-plane sectoral horn in the design of the box-horn on the SAR distribution is also examined. The results have been validated against published results in the literature.     

Coupling phenomena in concentric multi-applicator phased arrayhyperthermia systems

The coupling between the waveguide applicators of a four-element phased array hyperthermia system irradiating a three-layered cylindrical tissue model of circular cross section is analyzed theoretically. The fields inside the tissue layers are expressed in terms of cylindrical vector wave functions satisfying the corresponding wave equations, while the fields inside each waveguide are expanded in terms of guided and evanescent normal modes. Then, by implementing the appropriate boundary conditions, a system of four coupled integral equations is derived in terms of the unknown electric field distributions on the open waveguide apertures. This system is solved by expanding the unknown electric field on each aperture into waveguide normal modes and by applying a Galerkin's procedure. The self reflection coefficient and the mutual coupling coefficients are then determined and numerical results for a four-element phased array hyperthermia system are computed and presented for different waveguide applicator sizes and settings     

Microstrip antenna phased array with electromagnetic bandgap substrate

Uniplanar compact electromagnetic bandgap (UC-EBG) substrate has been proven to be an effective measure to reduce surface wave excitation in printed antenna geometries. This paper investigates the performance of a microstrip antenna phased array embedded in an UC-EBG substrate. The results show a reduction in mutual coupling between elements and provide a possible solution to the "blind spots" problem in phased array applications with printed elements. A novel and efficient UC-EBG array configuration is proposed. A probe fed patch antenna phased array of 7/spl times/5 elements on a high dielectric constant substrate was designed, built and tested. Simulation and measurement results show improvement in the active return loss and active pattern of the array center element. The tradeoffs used to obtain optimum performance are discussed.     

一种低成本星载宽角扫描相控阵天线设计

设计了一种工作于X 频段的星载圆极化相控阵天线。相控阵天线单元的馈电探针与连接器进行了一体化设计,消除了焊点,提高了阵面的可靠性;同时阵列单元周围加载金属腔体结构,降低了单元间的耦合,展宽了天线波束,提高了阵列的扫描增益;阵面为全金属结构,可实现相控阵的均温性与内部热量的辐射,阵面自身具有较强的空间抗辐照能力,同时也能对相控阵内部的有源器件提供良好的辐照屏蔽。相控阵有源组件和合成网络采用瓦片架构,具有轻量化和低剖面的特点。所设计相控阵天线具有±60°宽角扫描能力和4%的工作带宽。     

Theoretical and experimental study of monopole phased array antennas

A theoretical and experimental investigation of the mutual coupling in large two-dimensional periodic planar phased arrays of thin cylindrical monopoles is addressed. A plane wave representation of the active input impedance is used to analyze an infinite array of monopoles. A finite array analysis is used to compute the center element gain pattern and input impedance as a function of the array size and element position. The center element gain pattern is shown to have omnidirectional vertical polarization with a null on-axis and peak gain in the vicinity of50degfrom broadside. Measurements of the element gain pattern and mutual coupling for a 121-element passively terminated monopole square lattice array are shown to be in good agreement with the theory. The results of the infinite array analysis are compared to theoretical and experimental data in the literature for hexagonal lattice arrays.     

基于小型阵列试验的相控阵单元互耦特性研究

相控阵天线辐射单元的互耦特性对天线整体性能有着重要影响,而互耦与具体单元形式相关,因此模型复杂, 难以精确计算和预测。在阵元的小型阵列试验过程中,采用互耦测试的方法,对准八木振子、微带贴片、Vivaldi 单元 等几种典型宽带相控阵单元的互耦特性进行了实验研究,结果表明互耦对不同类型的单元影响大不相同,对单元特性 不仅有传统认为的负面作用,还可能有改善性能的作用,分析结果可供相控阵天线设计时参考;同时,利用测试数据 分析了小型试验阵列的规模对结果的影响,提出了小型阵列的规模依据。     

Arrays of horizontally polarized loop-fed slotted cylinder antennas

Measured center element gain patterns, voltage standing-wave ratio (VSWR), and mutual coupling for passively terminated arrays of horizontally polarized loop-fed slotted cylinder antennas over a ground plane are given. A seven-element hexagonal array is investigated in detail. The element gain pattern is shown to have a null at broadside with omnidirectional coverage along a constant cone angle from broadside. Maximum gain occurs close to50degfrom broadside which provides for wide-angle phased array scanning capability. The antennas are also configured in a linear array geometry, to investigate mutual coupling effects on the element gain pattern as the number of elements is varied. The element gain pattern is shown to converge for a relatively few number of elements and there is no indication of undesired blind spots.     

Experimental results of 144-element dual-polarized endfiretapered-slot phased arrays

Two 9×8×2 (144 element) dual-polarized endfire tapered-slot phased arrays have been built. Measured data for mutual coupling coefficients and scan-element patterns are presented. Also, element resonances, predicted by numerical infinite-array analysis are examined. The dimensions of the two arrays are identical. They differ in that plated-through vias have been repositioned to eliminate element resonances. One array was expected to operate from 1.0 to 4.6 GHz and the other from 1.0 to 5.9 GHz. It was found that, at low frequencies, the central elements are heavily affected by the finiteness of the arrays due to strong mutual coupling between array elements. Extrapolation of the observations indicates that a tapered-slot phased array, designed for wide-angle scanning, should be comprised of at least 30-40 rows and columns of elements to obtain low-frequency performance that is comparable to infinite-array predictions. In spite of the smallness of the array, predicted-element resonances could be identified by examination of the phase of the mutual coupling coefficients. Based on these observations, the plated-through vias are adequate to remove element resonances     

低互耦星载相控阵天线设计

介绍了一款工作于Ku频段的低互耦星载相控阵天线的设计方法, 采用在阵列单元周围加载金属腔体的方式降低阵列单元之间的互耦效应, 从而改善相控阵天线的方向图扫描特性.针对相控阵天线在二维±60°范围内低副瓣波束扫描的特点, 对5×5子阵和16×16阵列进行了研究, 验证了阵列的互耦降低方法的有效性和电性能.研究结果表明:相控阵单元间互耦小于-16 dB, 而相控阵单元在15.1~16.8 GHz电压驻波比小于2, 相对带宽11%;在频率为f₀±500 MHz范围内, E面3 dB波束宽度大于98°, 5 dB波束宽度大于113°, H面3 dB波束宽度大于113°, 5 dB波束宽度大于122°.在仿真设计的基础上, 研制了子阵天线试验样机, 测试结果与设计结果吻合良好, 证明了降低互耦方法的有效性, 天线单元方向图满足在±60°范围内波束扫描的要求, 可应用于相控阵雷达系统.     

有源相控阵天线的近场校准

为实现对相控阵天线的校准,降低幅相误差和阵元失效对天线性能的影响,提出了一种考虑互耦效应的近场校准方法。在利用近场扫描法完成逐一通道校准的基础上,使用旋转矢量法进行二次校准。在应用旋转矢量法（ REV)时,为使被测信号的变化明显,将大规模相控阵天线分为中间、边缘区域进行分区校准。通过二次校准可判定阵元是否失效,提高相控阵天线的幅相一致性;通过分区校准减小阵元间互耦的影响,缩短校准时间。仿真结果表明：此方法用于大型相控阵的校准具有较高的准确性,可改善校准结果。     

两种应用于宽带阵列天线的阵列单元

介绍了两种应用于宽带相控阵中的阵列单元,分析了每种天线的性能和优点,对天线单元进行了充分的设计、仿真和优化,仿真结果与实测结果基本一致。组成9×9的阵列,并对阵列中单元进行测量,对测量数据进行处理。结果显示出良好的宽带特性,具有较低的互耦等优点,可应用于三坐标雷达系统。     

超低副瓣偶极子相控阵互耦的研究＊

本文首次提出了从网络定义出发求偶极子阵列天线单元间互阻抗的方法,然后提出了用互阻抗矩阵来补偿单元间互耦的方法。计算结果表明:在扫描角不太大的情形下,用本文提出的互耦补偿方法是有效的。并在此基础上讨论了互耦对单元上电流分布规律的影响以及对副瓣电平的影响,为实现超低副瓣相控阵提供了详细的分析依据。     

On the empirical optimization of antenna arrays

Empirical optimization is an algorithm for the optimization of antenna array performance under realistic conditions, accounting for the effects of mutual coupling and scattering between the elements of the array and the nearby environment. The algorithm can synthesize optimum element spacings and optimum element excitations. It is applicable to arrays of various element types having arbitrary configurations, including phased arrays, conformal arrays and nonuniformly spaced arrays. The method is based on measured or calculated element-pattern data, and proceeds in an iterative fashion to the optimum design. A novel method is presented in which the admittance matrix representing an antenna array, consisting of both active and passive elements, is extracted from the array's element-pattern data. The admittance-matrix formulation incorporated into the empirical optimization algorithm enables optimization of the location of both passive and active elements. The methods also provide data for a linear approximation of coupling as a function of (nonuniform) element locations, and for calculation of element scan impedances. Computational and experimental results are presented that demonstrate the rapid convergence and effectiveness of empirical optimization in achieving realistic antenna array performance optimization.     

An affordable millimeter-wave beam-steerable antenna using interleaved planar subarrays

Design and fabrication aspects of an affordable planar beam steerable antenna array with a simple architecture are considered in this paper. Grouping the elements of a phased array into a number of partially overlapped subarrays and using a single phase shifter for each subarray, generally results in a considerable reduction in array size and manufacturing costs. However, overlapped subarrays require complicated corporate feed networks and array architectures that cannot be easily implemented using planar technologies. In this paper a novel feed network and array architecture for implementing a planar phased array of microstrip antennas is presented that enables the fabrication of low-sidelobe, compact, beam-steerable millimeter-wave arrays and facilitates integration of the RF front-end electronics with the antenna structure. This design uses a combination of series and parallel feeding schemes to achieve the desired array coefficients. The proposed approach is used to design a three-state switched-beam phased array with a scanning width of /spl plusmn/10/spl deg/. This phased array which is composed of 80 microstrip elements, achieves a gain of >20 dB, a sidelobe level of <-19 dB and a 10-dB bandwidth of >6.3% for all states of the beam. The antenna efficiency is measured at 33-36% in X band. It is shown that the proposed feeding scheme is insensitive to the mutual coupling among the elements.     

相控阵天线及其功率合成方法分析

相控阵天线是当前干扰设备研究领域的重要设备之一。在介绍相控阵天线特点及构成的基础上,重点分析了通道的相位不一致性、天线的驻波导致的反射损耗、阵列单元间的互耦、天线阵的合成效率等诸因素对相控阵功率合成效率的影响,并就达到一定的干扰功率进行了初步设计。     

基于FFT的相控阵雷达校准方法

相阵控天线由于单元间互耦,器件的制造,组装误差,老化,热变形和组件更换的影响而产生幅相误差,必须进行校准和补偿。文中提出一种新的校准方法,先在相同的频率和环境条件下分别进行ＦＦＴ外校准和初次ＦＦＴ内校准确定内外场校正系数,然后在雷达使用期间只需作天线ＦＦＴ内校准就可获得理想的精度,用一２４单元实验阵列对此作了实验验证。此方法具有低设备量和高校准精度,适用于一维,二维相控阵雷达,尤其适合于机载或地面     

约束优化实现超低副瓣相控阵的多阶振幅量化

利用约束非线性最优化方法研究超低副瓣相控阵激励振幅的量化综合问题,通过对相控阵天线优化模型加入适当的约束条件,实现了二维可分离超低副瓣相控阵天线多阶振幅量化和单元间互耦的直接修正,该方法适用于各种形式相控阵天线的量化综合,最后给出了一些计算结果。     

A DFT-based UTD ray analysis of large finite phased arrays on a grounded substrate

A discrete Fourier transform (DFT)-based asymptotic high-frequency, uniform geometrical theory of diffraction (UTD) ray solution is developed to describe, in closed form, the collective field produced by large finite phased arrays of printed antenna elements on a grounded material substrate. Such a DFT-UTD ray analysis yields useful physical insights into the large array radiation and scattering mechanisms. This is in contrast to the conventional array element-by-element summation for the radiated field which lacks the above useful properties. In the present work, any realistic arbitrary array current distribution, i.e., in the presence of array mutual coupling, is represented by a DFT expansion so that each term in the expansion becomes a simple uniform array distribution with a linear phase, which then directly facilitates the development of the asymptotic UTD ray solution. Furthermore, another significant advantage of the DFT is that for most practical array excitations, only a relatively few DFT terms remain dominant in the expansion and are sufficient to provide reasonably accurate results. Some numerical examples are presented to illustrate the utility of this collective DFT-based asymptotic UTD ray solution for large array fields.