Comparison of mutual coupling compensation to dummy columns in adaptive antenna systems

Compensation for mutual coupling in antenna arrays by matrix multiplication is compared to the use of dummy elements. A least squares estimation of the coupling matrix is made, including co- and cross-polar coupling. We show that compensation for measurements off the phase center is important as well as a proper assumption of the ideal element pattern. We study the performance of a dual polarized patch array with respect to far-field phase error, signal-to-interference reduction, and cross-polarization level. In all aspects, the performance of the compensation method exceeds or equals the use of dummy elements.     

一种新型极化捷变有源微带天线阵

本文提出了一种新颖的极化捷变放大器型有源微带天线阵,只要在馈电端电控单一有源电路就能实现整个微带天线面阵极化的捷变和信号的放大.利用角馈方形微带贴片设计了一副具有高隔离度和低交叉极化的新颖16元双极化面阵,并分析了天线阵的共极化和交叉极化方向图.介绍了有源电路的设计.该电路利用一专用电控移相器,通过改变场效应管(FET)栅极的直流控制电压,电控两极化端口间的0°或90°相差,实现天线阵由线极化到圆极化的捷变.低噪声放大器(LNA)不仅使有源天线增益提高12-14dB,而且改善了天线的驻波比带宽和隔离度.文中给出了无源双极化阵和有源阵的实验结果,证实了理论的有效性.     

Polarization-agile microstrip antenna array using a single phase-shift circuit

A novel polarization-agile microstrip antenna array is proposed, in which the polarization agility from linear to circular polarization for the whole array is realized easily by controlling a single phase-shift circuit. Using the corner-fed square patch element, a new 16 element dual-polarized array with high isolation and low cross-polarization is designed and analyzed by the extended multiport network method. A special FET phase shifter circuit is created, where 0/spl deg/ or 90/spl deg/ phase shift between dual ports is electrically switched. Experimental results are presented to verify the theory, and measured circularly-polarized radiation patterns show a boresight axial ratio of 0.5 dB. Another experiment that connects a low noise amplifier together with the phase-shift circuit is also introduced, realizing both polarization agility and power amplification with one active circuit.     

Performance and design procedure of dual parabolic cylindricalantennas

The radiation characteristics of dual parabolic cylindrical antennas are studied, and the dependence of the principal plane beamwidths and the peak cross-polarization on their geometrical parameters is determined. The antenna aperture is rectangular in shape and generates an elliptical beam pattern, with a beamwidth ratio that can be controlled by the main and subreflector focal lengths. The far-field patterns are determined by an extended aperture integration method that includes the contributions of the reflected and the main diffracted rays. It is found that the cross-polarization depends of the offset angle between the axis and the direction of the normal to the subreflector surface and can be minimized by optimizing the relative angle between the reflectors. Other pattern characteristics are controlled by the antenna geometrical parameters and the feed illumination. A procedure for the design of these antennas and the expressions for determining the reflector geometries are provided     

Iterative least-squares synthesis methods for conformal arrayantennas with optimized polarization and frequency properties

An iterative least-squares synthesis technique is presented for the optimization of the element excitation in conformal array antennas. This method allows the designer to have predefined goals for the shaped radiation pattern over a selected frequency band and for the polarization properties of the array. Linear or circular polarization can be used in the synthesis. Different kinds of synthesis goals can be set, whereby the copolarization or cross-polarization properties of the array are weighted or a narrowband or wideband design is sought. The amplitudes of the element excitations can be fixed. Several synthesis examples are presented for an array on a sphere with circular polarized elements. Broad-band and low cross-polarization designs are included     

Corner-fed microstrip antenna element and arrays for dual-polarization operation

A systematic study on the dual-polarized corner-fed microstrip antenna element and arrays with thin single-layer structure is presented. The impedance matrices and S-parameters of the element and arrays are investigated by the proposed extended multiport network method (EMNM). The co- and cross-polarization patterns are also analyzed. It is shown that this kind of antenna element has an isolation about 10 dB higher than that of a conventional edge-fed square patch. A series of new dual-polarized arrays of corner-fed patches have been designed and analyzed based on the EMNM. The experimental results of five arrays indicate that these arrays achieve an isolation of 27/spl sim/38 dB with a maximum of higher than 28/spl sim/58 dB and cross-polarization level of lower than -23/spl sim/ -30 at boresight, which are substantially better than those of similar dual-polarized arrays of edge-fed patches. All theoretical results are in good agreement with experimental ones.     

Planar Radiating Oscillator Using Butterfly-Shaped Patch Element and Spatial Power-Combining Array

A planar radiating oscillator using a butterfly-shaped patch element is described. To obtain an injection-locking range that can be changed and low cross-polarization, we used a butterfly-shaped patch. The patch element was able to change the injection-locking range while maintaining low cross-polarization, and two types of patch were compared. As one application, we designed and fabricated 1x2, 2x1 and 2x2 spatial power-combining arrays by using radiative mutual coupling. The 2x2 array was successfully operated with a single-bias supply without using a 3-D (three-dimensional) Fabry-Perot cavity. An equivalent isotropic radiated power of 2.5 W was measured at X-band.     

Reducing grating lobes due to subarray amplitude tapering

Subarray amplitude tapering is a simple, lower cost method to generate low sidelobes in an antenna's far-field pattern. Unfortunately, this simple technique also generates unwanted grating lobes. Placing the exact amplitude taper at the element outputs produces the desired far-field pattern, but the feed architecture is complicated and expensive. An alternative to these two techniques is described. A trade-off exists between sidelobe performance and simplicity of design. This trade-off consists of amplitude tapering the subarray outputs and the element outputs in such a way that the element amplitude tapers are identical for every subarray. In this way, the amplitude taper approximates the desired taper much better than subarray tapering alone, yet all the subarrays are identical. Thus, the feed design remains very simple.     

频率分集均匀圆阵MIMO雷达距离依赖波束形成

均匀圆阵(UCA)与多输入多输出(MIMO)雷达的结合可在具备UCA雷达主要优点的同时兼有MIMO 雷达的优势。然而,UCA-MIMO雷达的波束形成与距离无关,该特点限制了其抑制特定距离干扰的性能。文中提出频率分集UCA-MIMO雷达距离依赖波束形成方法。该方法中UCA的每个阵元发射具有微小频率步进的不同频率,从而远场的信号积累与距离有关,进而波束形成依赖于距离。仿真实验表明了该方法的有效性。     

一种提高交叉极化隔离度的16元微带阵列天线

在现代通信中,特别是卫星通信,有时需要比较高的交叉极化隔离度。对于传统的微带阵列天线来说,由于其馈电网络与阵元均处于同一侧,不仅会产生互耦,影响增益,并且交叉极化隔离度也不能满足广大用户的要求。在此提出一种新型的馈电结构,旨在提高其交叉极化隔离度。从仿真中可以看出,交叉极化隔离度能达到40 dB以上,为实现更大型微带阵列天线网络做出一定的理论实践和工程指导。     

交叉极化及副瓣约束的任意阵列最优方向性综合

本文根据给定的期望极化方向,定义了扫描波束的期望主极化和交叉极化方向,并进一步给出了主极化方向性系数的定义,它可以更为准确的表征天线集中辐射主极化分量的程度.在没有副瓣约束和交叉极化约束的条件下,给出了任意阵列主极化方向性系数最优解的解析表达式.并且,在含副瓣约束、零陷约束以及交叉极化约束的条件下,我们发展了一种基于凸优化的高效数值综合方法,实现多约束条件下的主极化方向性系数的优化.数值阵列综合结果表明了本文所提出的最优主极化方向性系数解析解的正确性,以及这种可以综合考虑副瓣约束、零陷约束和交叉极化约束的数值方向性优化方法的有效性.     

A shaped single reflector offset antenna with lowcross-polarization fed by a lens horn

A novel compact primary-fed offset reflector antenna with the potential of radiating circular as well as elliptical beams with low cross-polarization, is proposed. The reflector is fed by a horn with a phase-correcting lens in the aperture. Compared to the dual-reflector offset antenna, the concept is easier to assemble and mechanically more robust. The antenna has been synthesized and analyzed by computer programs resulting from modifications of corresponding PO programs for dual-reflector offset antennas. The synthesized antenna exhibits similar cross-polarization, side-lobe level, and aperture efficiency as those of dual-reflector offset antennas, although the one-to-one correspondence between zero cross-polarization and conformal mapping from the feed to the aperture, is not exactly valid for this approach     

Four-core fiber-based bending sensor

A novel four-core fiber-based bending sensor has been proposed. The four-core fiber is used as the sensing element, the four cores of the fiber act as a four-beam interferometer, and the far-field interferogram grids with periodical distributions are formed on the fiber output end. Since the phase difference is a function of the radius of curvature, the change of the radius of curvature shifts the far-field interferometric grid pattern. A low-coherence laser diode with wavelength of 650 nm is adopted to illuminate the fiber, and the interferogram pattern in the far-field is recorded by a CCD camera. The relationship between the far-field grid pattern intensity distribution and the radius of curvature is established theoretically and confirmed experimentally.     

Novel active FET circular patch antenna arrays for quasi-opticalpower combining

This paper discusses two-dimensional planar arrays of weakly coupled active circular patch antennas suitable for quasi-optical power combiners. A novel radiating element that has low cross-polarization is described. A two-dimensional array analysis was developed to address radiation pattern and phase problems. Equivalent isotropic radiated power levels of 1.5 W for a two by two FET array and 3.8 W for a two by four FET array have been obtained at X-band     

准光学馈电系统设计与分析

针对遥感卫星对于多频段、多极化探测的应用需求,设计了一套毫米波辐射计天线前端准光学馈电系统,可以实现54 GHz和183 GHz两个频段、H/V双线极化、4个通道同时接收电磁辐射信号,完成地球大气温湿度的有效探测。通过对馈电网络进行仿真建模和分析计算,可以验证馈电系统的输出参数完全满足设计指标要求,最后通过对原理样机各通道远场辐射参数的实验测试,包括照射半张角、交叉极化水平、波束效率等,测试与仿真结果一致,有效地验证了准光学馈电系统设计方案的合理性与可行性。     

基于衍射光栅的远场焦斑测量新方法

提出一种基于一维线衍射光栅的焦斑重构和远场测量新方法,从理论上分析了新方法在拓展测量仪器动态范围、提取远场焦斑高频旁瓣信息的有效性及方法的适用条件。基于实验室现有的一套远场测量系统平台及自行设计的一维线衍射光栅,以远场环围能量(PIB)曲线作为检验新方法有效性的指标,通过数值仿真和实验相结合考察了新方法的有效性,并从准确测量远场焦斑质量的角度探讨了不同减阈值的去噪方式对焦斑重构结果的影响,对结果进行了分析讨论。     

微带线馈电的宽带单层贴片天线

微带贴片天线已广泛应用于雷达系统,文中介绍了一种新型背腔式单层微带贴片天线,辐射贴片采用微带线馈电,为增加工作带宽,提供了两种不同的贴片形状,第一种是E形贴片,仿真及测试结果表明,此种单元在驻波比优于2的条件下可实现45%的阻抗带宽,但该单元的波瓣带宽较窄。为抑制交叉极化,通过在E形贴片上开四个槽,得到了第二种改进的E形贴片。该单元可实现14%的频带内驻波比优于1.5,同时交叉极化优于-15dB。对C波段8×16单元实验小阵的测试结果表明,该天线在17.9%的频段内具有良好的交叉极化性能及较高的工作效率。     

Ice depolarization of the COMSTAR beacon at 28.56 GHz during low fades and correlation with radar backscatter

Radar correlation with significant ice depolarization events accompanied by low copolarization fades of the 28.56-GHz COMSTAR beacon signal are described for an experimental program at Wallops Island, VA. Using a Faraday switch at the front end of the receiver, the copolarization and cross-polarization levels of the 28.56-GHz beacon signal are sequentially monitored. A nearby high resolutionS-band radar pointing along the Earth-satellite path monitors the simultaneous ice and rain reflectivity. Excellent correlation is noted between the cross-polarization events and relatively large and extended ice reflectivities along a segment of the Earth-satellite path at altitudes near and above the 0°C isotherm. The radar and receiver data strongly suggest the cross-polarization mechanism is due to a hailshaft which intersects the path at altitudes well below the 0° isotherm. Since the intervening ice results in a cross-polarization signal which either adds or subtracts to the cross-polarization antenna residual, a method is described to remove the residual from the resultant measured cross-polarization level, without employing a phase measurement. Cumulative, month-of-year and time-of-day statistics associated with the depolarization signals are established.     

中心波长及脉宽对能量叠加光束远场的影响

多束激光的远场叠加对于提高远场靶面能量是一种有效的方法,单元光束的参数的变化对于远场合成光束都会产生影响。为了分析脉冲激光参数控制对远场能量分布的影响,利用夫琅禾费衍射积分公式导出了4束普通脉冲高斯光束合成的远场光强的解析式,并整理了激光中心波长和脉宽的改变对远场叠加后能量分布的影响之间的具体关系。通过MATLAB的数值模拟,结果表明:当光束的中心波长减小或者脉冲宽度减小时,远场能量向中心轴上汇聚,远场轴上光强增加。当轴上光强相对于理想中心波长和脉宽的远场轴上光强的变化率小于5%,中心波长变化率最大不能超过7.89%,或者脉宽变化率最大不能超过91%,因此,中心波长的变化对于远场光强分布的影响比脉宽更大。     

On the cross polarization of asymmetric reflector antennas for satellite applications

It is well known that focussed, axial symmetrical reflector antennas collimate the co- and cross-polar components of the primary field separately, i.e., the reflector does not create a contribution to the cross polarization of the far-field. By a simple extension of a classical physical argument it is demonstrated that this separability does not depend on the symmetry of the antenna, and that it, therefore, holds even for off-set fed reflectors. A new mathematical formulation of the collimation is derived in which this is shown. Yet the separability does depend on how the co- and cross-polar fields are defined, and the cross polarization of feeds for asymmetric reflectors is discussed in detail in the light of this. It is further suggested how to design low cross polarization feeds for off-set fed antennas. As a consequence of the separate collimation such feeds will lead to low cross-polarization of the secondary fields. Two simple examples are treated. The only limitations of the results are those due to the application of the aperture field version of the physical optics approximation.