Canonical sources and duality in chiral media [antenna arrays]

The authors examine the characteristics of antenna arrays embedded in unbounded chiral media using the Green's dyadic for electric sources and the Green's vector for magnetic sources. The purpose is to bring to light the new characteristics of sources, both point and extended, which interact with this medium and to examine general characteristics of sources located in a medium with handedness. Very simple quality relations are presented that are characteristic of chiral media when the results are written in terms of the circular eigenmodes. Appropriate measures of chirality such as the chirality admittance and impedance and a dimensionless chirality factor are introduced as needed. It is shown that, in the far field, both point and extended sources, whether electric or magnetic, radiate two electromagnetic eigenmodes which are of opposing handedness. Sources that access only one of the eigenmodes of the medium are demonstrated. Several applications of the results and array performance in chiral media are noted     

A voltage-matching method for feeding antenna arrays

A method for feeding antenna arrays is presented. Each element of the array is connected with transmission line sections. The first two sections are connected to a common point where the voltage from both sections is the same. The common point is connected with a new transmission line which is also doing the same with the third section. The procedure is continued until the last common point will be connected to a single source. A formulation for the antenna currents as a function of the frequency is also given. Some examples show the applicability of the method     

A short design method for nonuniformly spaced antenna arrays

A design method is presented for symmetrical nonuniformly spaced linear arrays. Element positions are easily found if one element position is given. Instead of restricting the cosine functions in the array factor, a constraint is placed upon the arguments of the cosine functions. For an array of2Nelements, one obtainsN - 1equations inNunknowns, which can be solved sequentially instead of simultaneously. The array designs are not optimum, but the simplicity of this method will allow arrays to be designed quickly. These arrays could inturn be used as preliminary steps toward more rigorous studies.     

A semiblind method for transmit antenna arrays in CDMA systems

Using a transmit antenna array (TAA), the downlink beamforming is able to improve the performance of wireless communication systems. We propose a semiblind downlink beamforming method based on channel reciprocity of the wireless channels for code-division multiple-access (CDMA) systems equipped with TAA. In the proposed semiblind method, it is shown that the feedback delay can result in performance degradation under a time-varying fading channel environment. Hence, the performance of the semiblind method is satisfactory only when the maximum Doppler frequency is low or the feedback delay is not significant. To overcome this difficulty, the channel prediction is considered. Using the channel predictor, the semiblind method can provide a reasonable performance for a moderate maximum Doppler frequency (about a few hundred hertz). For theoretical performance analysis, upper, and lower bounds of the bit error probability under a fading channel environment are derived     

A combined full-wave BCG-FFT method for radiation of microstrip antenna arrays

A method of combining BiConjugate Gradient(BCG) with Fast Fourier Trans-form(FFT) to analyze the radiation of microstrip antenna arrays is presented, where the spatially discrete BCG-FFT for analyzing microstrip structure is used and the del operators on Green's functions are transferred from the singular kernel to the expansion and testing functions. The resultant equations are solved by using BCG method in which the matrix-vector product is evaluated efficiently with FFT. The calculated patterns are in good agreement with the measured data.     

A novel approach for focusing electron beams using low-cost ceramicgrid [field emitter arrays]

A low-cost ceramic grid was used as a stand-alone focusing electrode in field emitter arrays to obtain high brightness and small electron beam size. The ceramic grid with an array of 200-μm holes was made from DuPont 591 with low-cost equipment. Beam size is controllable by the voltage applied to the focusing grid. Light intensity profiles were measured and analyzed. The full width at half maximum (FWHM) of the light profile excited by electron emission from 30-μm wide field emitter arrays is 60 μm at 5000 V with 6 mm anode-cathode separation. At an anode voltage of 2000 V and gate voltage of 55 V, focusing is optimized at a focusing voltage of 30 V. Arc-free operation at 10 kV was achieved, thereby promoting improved phosphor efficiency. This focusing approach may lead to improve lifetimes for field emission displays and other vacuum microelectronic devices by significantly increasing the total vacuum volume and providing a means for improved getter utilization     

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     

A combined full-wave CG-FFT method for rigorous analysis of largemicrostrip antenna arrays

An accurate and efficient technique is presented for the analysis of large microstrip antenna arrays. The technique consists of an amalgamation of a spatially discrete scheme, consisting of the CG-FFT method and the complex discrete image (CDI) technique. The unique feature of this approach is the use of the spatially discrete CG-FFT for analyzing microstrip structures. The aliasing and truncation errors are thoroughly eliminated in this approach. In addition, the grad-div operators are transformed from singular Green's functions to differentiable expansion and testing functions by using Galerkin's procedure, thereby improving the accuracy and the rate of convergence. To show the accuracy and efficiency of this technique, a number of microstrip arrays, including a large microstrip reflectarray, have been studied. It is found that the simulations carried out using this technique are in very good agreement with measurements     

DOA estimation for noninteger linear antenna arrays with moreuncorrelated sources than sensors

We investigate direction-of-arrival (DOA) estimation involving nonuniform linear arrays, where the sensor positions may be noninteger values expressed in half-wavelength units, with some number of uncorrelated Gaussian sources that is greater than or equal to the number of sensors. We introduce an approach whereby the (noninteger) co-array is treated as the most appropriate virtual array when considering an augmented covariance matrix. Since such virtual arrays have an incomplete set of covariance lags, we discuss various completion philosophies to fill in the missing elements of the associated partially specified Hermitian covariance matrix. This process is followed by the application of an algorithm that searches for a specific number of plane wavefronts, yielding the minimum fitting error for the specified covariance lags in the neighborhood of the completion-initialized DOA estimates. In this way, we are able to resolve possible ambiguity and to achieve asymptotically optimal estimation accuracy. Numerical simulations of DOA estimation demonstrate a close proximity to the Cramer-Rao bound     

Synthesis method of series-fed microstrip antenna arrays

A method for non-uniformly spaced series-fed rectangular microstrip array synthesis is given. By this approach the problem of patch array design turns out to be slot array synthesis. The resulting equivalent configuration gives the necessary parameters for the microstrip array geometry. Applications on Taylor, Bayliss and shaped-beam patterns show the validity of the method     

一种利用相控天线阵综合扇区波束的方法

提出一种利用遗传算法优化得到的阵列天线综合扇区方向图的方法，并分析了其性能及对误差的敏感度。该阵列可用于TD-SCDMA系统实现分扇区技术和波束赋形技术的结合使用。     

The point objective function for optimization of side lobes of linear antenna arrays

A new form of objective function is suggested for the problems of point optimization of complex radiation patterns of discrete antenna arrays. The function takes the properties of individual antenna radiators and the antenna array phase characteristic into account. Several examples of various antenna arrays help consider some properties of the point objective function and peculiarities of application of optimization of side lobes’ level using this function.     

一种考虑互耦的脉冲天线阵列快速计算方法

基于有源单元方向图思想,提出了一种可用于计算脉冲天线阵列时域辐射场的快速方法.该方法在考虑单元间互耦的情况下,将大型阵列的时域辐射场计算问题转化为一个小型阵列的计算问题,大大地减少了计算量.采用文中的阵列综合方法,结合有限积分法软件,仅对一个5×5元阵列进行模拟,即可推算出大型阵列的远场方向图,其计算时间不超过全波模拟时的十分之一.计算结果与仿真软件的仿真结果吻合较好,验证了方法的正确性.     

一种考虑互耦的脉冲天线阵列快速计算方法

基于有源单元方向图思想, 提出了一种可用于计算脉冲天线阵列时域辐射场的快速方法.该方法在考虑单元间互耦的情况下, 将大型阵列的时域辐射场计算问题转化为一个小型阵列的计算问题, 大大地减少了计算量.采用文中的阵列综合方法, 结合有限积分法软件, 仅对一个5×5元阵列进行模拟, 即可推算出大型阵列的远场方向图, 其计算时间不超过全波模拟时的十分之一.计算结果与仿真软件的仿真结果吻合较好, 验证了方法的正确性.       

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.     

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.     

A new optimization technique for adaptive antenna arrays

An adaptive nulling algorithm for adjusting the array weights under the soft constraint of the weight norm being very much less than 1 or equal to 1, based on the measured correlations between the array and element outputs, is described. The algorithm can be regarded as an extension of the constrained least-mean-square algorithm. It is derived from the same concept of signal and noise subspaces defined in the multiple signal classification (MUSIC) algorithm. One of the unique features of the present algorithm is that the number of the iterations required to adapt the array weights to form nulls is exactly equal to the number of interferers     

A horn-reflector antenna for high-performance submillimetre-wave imaging arrays

We have developed an antenna for high-performance submillimetrewave imaging arrays. The antenna comprises a corrugated horn with an off-axis paraboloidal reflector at its aperture. The corrugated horn is machined directly into two halves of a split aluminium block. This approach avoids electroforming and is compatible with E-plane circuit technology. The resulting antenna is light weight and is ideal for space applications. For compatibility with submillimetre-wave optics, the the behaviour has been calculated by using Gaussian-Hermite modes, and the integrity of the theory has been verified by modelling the behaviour of a 17GHz antenna. The manufacturing procedure has been investigated by machining and testing a horn-reflector antenna for 450–500GHz. Our next step is to extend the technique to 1THz.     

A decorrelating detector for use with antenna arrays

This paper addresses the problem of synchronous CDMA communications when, due to bandwidth limitations, signature waveforms have relatively large correlations. A receiver which uses the multiple received signals available from an antenna array is proposed and its performance analyzed. This receiver may be interpreted as a multichannel extension of the decorrelating detector and therefore shares its immunity to near-far effects. The receiver uses the discrimination afforded by the antenna array to effectively reduce the correlation between users' transmitted signals thereby avoiding the reduction in performance which occurs in the single channel decorrelator when signature correlations become significant.This work was supported by the National Science Foundation under Grant MIP-9202081. This paper was presented in part at the International Conference on Communications, ICC'94, New Orleans, Louisiana.