二元喇叭天线阵列的互耦研究

通过同轴线给天线馈电的方式,采用细导线FDTD方法模拟同轴线,研究了同轴传输线口径处内、外场之间的耦合,并分析了二元TEM喇叭天线阵的耦合问题,通过对单一喇叭进行馈电计算了天线阵单元的自阻抗和互阻抗.结果表明.在所考虑的频段内自阻抗和互阻抗不随频率的变化而变化,具有很好的宽带性能.     

Modal analysis of waveguide antennas with arbitrary cross sections

An approach is given to analyze the modal coupling of open-ended waveguides with arbitrary cross sections located in a conducting screen. The presented theory enables the determination of reflection characteristics of a single waveguide, as well as the analysis of mutual coupling between elements in waveguide antenna arrays. The field inside each waveguide is expressed as a sum of the transverse-electric and transverse-magnetic modes and expressions for the mutual admittances of modes excited at the aperture are obtained using a direct integration method. From these expressions, the mode reflection and conversion coefficients are determined. Computed and measured results are presented. Furthermore, this approach has been used to design a new type of horn antenna with high return loss and equal radiation patterns in the two principle planes     

Cross coupling in a five horn monopulse tracking system

A model is developed which explains the observed effects of secondary pattern crosstalk in a five horn circularly polarized monopulse tracking system. The model predicts unstable operation and loss of track for sufficiently depolarizing targets as well as polarization dependent uncertainties in the angular location of off-axis targets. The cross coupling is characterized by two complex coupling coefficients between adjacent horns in the monopulse feed system. This characterization is assumed to be valid irrespective of whether the observed secondary pattern effects are the result of mutual couplings within the feed structure itself or caused by cross-polarized backscatter from the paraboloidal reflector. A "ridge" and "nonridge" polarization terminology is adopted which is physically related to the fact that the error horns in a five horn circularly polarized system are heavily ridge loaded for one linear polarization and not the other.     

互耦作用对MIMO系统信道容量的影响

简单概括了无线多输入多输出（MIMO）系统及其信道容量,应用矩量法分析了因互耦作用引起的天线阵各阵元辐射图的变化,进而应用已提出的射线追踪模型分析了一个4.4MIMO系统接收端阵元间距不同时互耦作用对信道容量的影响。仿真结果说明在接收端使用多天线,阵元间距不可能太大的情况下,考虑互耦作用后,在小阵元间距（d=0.4λ）时就可得到较大的信道容量。得出结论在接收端阵元间距较小的情况下,互耦是一个有利的因素,在系统分析和设计时可以有效地加以利用。     

Diagonal horn integrated with micromachined waveguide forsubmillimetre applications

The feasibility of coupling silicon micromachines rectangular waveguide to a modified diagonal horn antenna using a model at 110 GHz is demonstrated. The antenna patterns obtained are similar to those obtained with a standard diagonal horn. A method of reducing the on-axis cross polarization response of diagonal horns is also presented     

大型平面阵列天线散射场的快速计算方法

基于子阵思想,提出利用小型平面阵列中的各天线单元的散射场,来等效大型平面阵列中相似阵列环境下的各单元的散射场,进而利用叠加定理来计算大型阵列的总散射场.并通过公式推导,进一步简化了该方法的操作过程,将大型平面阵列的散射计算问题转化为四个小型平面阵列的散射总场计算问题,显著减小了计算量,同时避免了逐个计算单元场而带来的操作复杂度.计算结果与HFSS仿真结果基本一致,验证了方法的正确性.     

Scanning and impedance properties of TEM horn arrays for transientradiation

A general concept for ultrawide-band array design using interconnected transverse electromagnetic (TEM) horns is described. At high frequencies (wavelength small compared to unit cell dimensions), the mutual coupling between elements is small and, consequently, the input impedance depends only on the lattice dimensions and not on either scan angle or frequency. At low frequencies (wavelength large compared to unit cell dimensions), the mutual coupling is purposefully made large, by interconnecting the elements to maximize the low-frequency performance. This paper presents the results of analyses using a periodic hybrid finite-element approach to calculate input impedance and scanning performance of generic TEM horn arrays. The limiting case, the planar bicone, is shown to have the frequency-independent property of a self-complementary antenna, making it a useful case for establishing the effects of feed region geometry. Although it radiates bidirectionally, it has the interesting property that its broadside-scan frequency response in the array environment is absolutely flat up to the grating lobe onset limit. A TEM horn array is more unidirectional, but as a consequence suffers both oscillatory variations in the input impedance with frequency and increased limits on minimum achievable rise time     

一种可用于卫星导航抗干扰天线的降耦方法

针对基于功率倒置算法的空时自适应抗干扰技术中天线阵元间互耦误差严重恶化算法性能这一问题,分析比较了目前常见的应对解决方案,并提出一种新的可用于抗干扰卫星导航终端的天线阵列降耦方法。该方法通过在卫星导航抗干扰天线阵列中加载电磁谐振吸波器,降低天线阵元间互耦。实验数据表明,利用该方法可以使阵元间互耦降低10 dB,使抗干扰接收机最大抑制干信比提升5 dB。     

Linear array of woodpile EBG sectoral horn antennas

A technique is described for creating linear array antennas that conform to the natural stacking sequence of the woodpile electromagnetic bandgap (EBG) material. Each element in the linear array consists of a woodpile EBG sectoral horn antenna. The electromagnetic confinement mechanism within each horn antenna relies wholly on the 3-D EBG of the woodpile material. The array element has a typical sectoral horn pattern with a directional beam in one principal plane and a broader beam in the other. The bandwidth of the sectoral horn is almost equal to that of the defect EBG waveguide. Measured and theoretical results for radiation patterns, impedance bandwidth and gain of a sectoral horn antenna made from alumina are described, and theoretical results for a design made from silicon are presented. It is shown that the layer-by-layer nature of the woodpile EBG material enables sectoral horn antennas to be easily stacked together in the E-plane to create linear arrays. Analysis of the mutual coupling as a function of element separation and its effect on reflection coefficient are presented for a two-element linear array in silicon. Theoretical analyses for fixed and scanned beam linear arrays of silicon woodpile EBG sectoral horns are described and finite-difference time-domain results are compared with array theory. The fixed beam arrays are designed for high directivity while the scanned beam array enables wide angle beam steering through the use of parasitic array elements.     

Analysis of an octagonal micromachined horn antenna forsubmillimeter-wave applications

An analysis is presented of a new horn antenna, fabricated by a novel micromachining technique, that uses crystallographic etching of silicon and ultraviolet lithography of an ultra-thick photoresist (SU-8). The horn was found to have low cross-polarized field levels and a predicted Gaussian coupling efficiency of 92.5%. The horn shape is governed by the crystal planes of the silicon substrate and the thickness of the photoresist and has up to four independent design parameters that allow a wide range of antenna patterns. A design for the horn that yields symmetric beam patterns was investigated by computer analysis, microwave scale modeling, and measurements of a micromachined horn at 585 GHz. The major features of the 585-GHz beam patterns agree well with the computer-generated and scaled beam patterns. We have thus demonstrated a new micromachinable horn that has great potential for integration into array structures     

Integrated modeling of microwave food processing and comparison with experimental measurements.

This paper presents an integrated electromagnetic and thermal model for the microwave processing offood packages. The model is developed by combining the edge finite element formulation of the 3-D vector electromagnetic field in the frequency domain and the node finite element solution of the thermal conduction equation. Both mutual and one-way coupling solution algorithms are discussed. Mutual coupling entails the iterative solution of the electromagnetic field and the thermal field, because the physical properties are temperature-dependent. The one-way coupling is applicable when the properties are temperature independent or this dependence is weak. Mesh sensitivity and shape regularity for the edge element based formulation for computational electromagnetics are discussed in light of available analytical solutions for a simple wave guide. The integrated model has been used to study the electromagnetic and thermal phenomena in a pilot scale microwave applicator with and without the food package immersed in water. The calculated results are compared with the experimentally measured data for the thermal fields generated by the microwave heating occurring in a whey protein gel package, and reasonably good agreement between the two is obtained.     

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.     

A Novel Method for High-Power Thermal Vacuum Testing of Satellite Payloads Using Pickup Horns

This paper presents the development of a novel method for high-power thermal vacuum (TVAC) testing of satellite payloads using pickup horns (PUH). It describes the design, manufacture, and qualification results for a Ku-band pickup horn, followed by high-power thermal vacuum test results of a Ku-band satellite for fixed satellite service. Based on the successful demonstration of this method, a generic pickup horn (GPUH) - with improved performance over a large bandwidth, covering 7.0 GHz to 21.0 GHz - was developed for testing of X-band, Ku-band, and Ka-band satellite payloads. Detailed design and qualification aspects of the generic pickup horn are addressed, including measured results. This method has been successfully employed for high-power thermal vacuum testing of three different satellites at Lockheed Martin Commercial Space Systems (LMCSS), and is the planned testing method for all future payloads.     

Compact multimode horn with low sidelobes for global Earth coverage

A new multimode corrugated horn is described for full-Earth coverage from a geostationary satellite. The horn has low sidelobes, low cross polarization, and is compact. We outline the design of this horn and compare its performance with other circular horn types, including conventional single and multimode-corrugated horns and dielectric loaded horns. A design was fabricated and measured results are described for return loss, radiation patterns, and axial ratio. These measurements demonstrate excellent agreement with computer predictions using mode-matching software     

Parametric design and analysis of multiple-beam reflector antennas for satellite communications

This paper presents the parametric design and analysis of multiple-beam reflector-antenna systems employed for satellite communications. It is based on extending the earlier work of Rao (see IEEE Antennas and Propagation Magazine, vol.41, no.4, p.53-59,1999) by taking into account the efficiency of the horn and pointing error of the satellite in the design of the multiple-beam antennas (MBAs), and by analyzing the edge-of-coverage directivity and co-polar isolation (C/I) performance. Design and analysis equations are developed for the multiple-beam antennas using offset parabolic-reflector antennas by including various design parameters such as the number of reflectors, the number of frequency cells, the focal-length-to-diameter (F/D) ratio, the horn efficiency, and the pointing error. The analysis employs a quasi-Gaussian beam representation for the primary and secondary patterns in order to take into account the effect of the sidelobes. Results of the analysis given in this paper agree well with rigorous computations based on physical optics analysis of the antenna radiation. Design curves showing the impact of horn efficiency on the C/I performance of multiple-beam antennas are presented for various frequency-reuse schemes.     

Mutual induction and the effect of host conductivity on the EM induction response of buried plate targets using 3-D finite-element analysis

A finite-element analysis of electromagnetic induction (EMI) in the presence of multiple buried metal targets is undertaken for the purpose of unexploded ordnance (UXO) detection and discrimination. The effects of mutual coupling between metal targets and the host conductivity are shown to be important. At high frequencies, mutual coupling is strong, and effects of host conductivity are relatively minor. At lower frequencies near the resistive limit, EMI responses are very small, but the effect of host conductivity becomes important. This is due to the galvanic current flow in the host medium that dissipates charge accumulations on the host/target interfaces. Qualitative analysis of induced current patterns in metal targets demonstrates that mutual coupling is strongly affected by target orientation and skin depth. Rigorous forward modeling of EMI responses is essential to understanding UXO sensor signatures so that discrimination between live UXO items and harmless fragments and clutter may become possible.     

A mutual coupling study of linear and circular polarized microstrip antennas for diversity wireless systems

In this paper, an analysis of mutual coupling is presented to examine the benefits of orthogonal polarizations and patterns for adjacent microstrip antennas. The mutual coupling between two linear polarized antennas orientated in parallel polarizations (E and H plane) is reduced using low dielectric constant materials. The mutual coupling can be reduced an additional 20-35dB at the same inter-element spacing when adjacent elements are orientated in orthogonal polarizations, O plane. Similarly, the mutual coupling between two circular polarized antennas orientated in the parallel polarization is reduced using low dielectric constant materials. However, the reduction in mutual coupling between two circular polarized antenna elements orientated in the O plane is only an additional 1-6 dB. The mutual coupling between a linear polarized sum beam (1/2/spl lambda/) and difference beam (1/spl lambda/) antenna is reduced 20-35 dB below the case when using identical antennas only in the H- and O-planes. Compact two- and four-element multielement antennas with inter-element spacings less than 0.15/spl lambda/ are fabricated and the S parameters and radiation patterns are measured.     

阵列天线散射条件下的互耦校正

当阵列存在近场散射源时,互耦效应的分析和校正更加繁杂,这就导致了阵列互耦矩阵的参数化建模需要做进一步的扩展,使得互耦矩阵不再为方阵。然而现有的参数化互耦校正方法均假设互耦矩阵是一个具有特殊数学结构的方阵,对非方阵的互耦矩阵模型不适用。本文通过引入少量远离阵列且相互间隔较远的辅助阵元（互耦效应可以忽略）和方向未知的校正信源,提出了一种阵列天线散射条件下的互耦校正的参数估计算法。首先,推导了扩展后的非方阵互耦矩阵系数与方位依赖的幅相误差的等价关系;然后,对每次单源实验,得到校正源方位和各阵元方位依赖的幅相误差的联合估计,建立估计的幅相误差以非方阵互耦系数为参数的方程;最后,将多次单源校正得到的方程进行整合构建方程组,利用Tikhonov正则化方法求解不适定方程组实现互耦系数的有效估计,进而对阵列互耦进行校正。计算机仿真实验结果表明所提算法可以很好地解决阵列天线散射条件下的互耦校正问题,从而验证了算法的有效性。      

Mutual coupling on a cylindrical array of waveguide elements

This communication presents a modal approach for investigating mutual coupling on a cylindrical array of waveguide elements. Computed results are given in the form of element patterns and are compared with measured patterns.     

Phased array antenna calibration and pattern prediction usingmutual coupling measurements

A technique which utilized the inherent mutual coupling in an array to both calibrate and predict the radiation patterns of a phased-array antenna is investigated. The only restriction of the technique is that the ability to transmit and receive with pairs of the array elements is required. The theory associated with array mutual coupling and its relationship to both array calibration and array patterns is discussed. The design of a test bed phased-array antenna is covered. The mutual coupling technique (MCT) is used experimentally to calibrate the test array as well as to predict the array radiation patterns. It is shown that the results obtained by MCT are in good agreement with conventional far-field measurements