Analysis of an EHF aplanatic zoned dielectric lens antenna

Zoned dielectric lenses, designed for wide-angle scanning characteristics, are serious contenders to reflector systems for multiple-beam communications and radar applications at EHF frequencies. An analysis is presented in which the zoned lens is approximated by an ideally thin spherical shell (phase transformer) in evaluating the phase aberrations in its aperture plane which are caused by off-axis scanning and deviations from the design frequency. Those results are used to produce a set of universal curves which predict the decrease in directive gain of the lens as a function of scan angle and frequency. Gain and radiation pattern measurements on a90 lambdazoned dielectric lens show agreement with these predictions and with ray-tracing and geometric optics calculations. This study establishes the validity of the spherical shell analysis as a means for rapid estimation of lens parameters for specific system requirements.     

An experimental completely overlapped subarray antenna

A completely overlapped subarray antenna was designed, fabricated, and tested to demonstrate its broad-band, low sidelobe, wide scan angle performance. It uses time delay steering at the inputs to a transform feed, which illuminates a phase-shifter steered objective lens. The transform feed is a Rotman lens and the objective is a cylindrical bootlace lens, both of which are parallel plate waveguide cavities with coaxial probe elements. The signal bandwidth goal of 20 percent (8.1-9.9 GHz) at55degscan was met easily, however, achieving the peak sidelobe goal of - 30 dB proved more difficult because of internal reflections in the Rotman lens beamformer. A brief summary is presented of the completely overlapped subarray antenna (COSA) concept to explain the detailed design of our experimental model. Antenna pattern and S-parameter measurements illustrate the operating principles, the difficulties encountered, and the results achieved.     

Optical technique for broadbanding phased arrays

An optical method for broadbanding a phased array is considered. A narrow band feed-through aperture lens comprised of pick-up elements, radiating elements, and360degtype phase shifters is fed by a small feed array with an intervening passive lens. The lens has fixed frequency-sensitive properties. The feed array has variable time delay compensators which are selected in accordance with the desired scan angle in the far field. Using geometrical optics, design formulas are derived that relate bandwidth and scan angle to the minimum number of variable time delayers. To demonstrate performance, diffraction theory is used to calculate patterns, sidelobe levels, and efficiencies as a function of bandwidth and scan angle out to50degscan for several aperture sizes. In the worst cases, the optical system provides somewhat less gain than the comparable constrained subarray antenna; however, it always provides much better sidelobe levels.     

Modeling and Characterization of Microstrip-to-Coaxial Transitions

A simple circuit model for the transition from a Iossy microstrip to coaxial line has been developed on an experimental basis. The proposed model can be used to predict accurately the insertion loss and insertion phase over a wide frequency range. Since explicit formulas for the model element values are given, these elements, representing the parasitic of the transitions, can be taken into account very easify when the microstrip is used as a test fixture for measuring the parameters of solid-state devices. The practical use of the model has been examined for several Z/sub 0/=50-omega lines on both Epsilam-10 and 99-percent alumina substrates with standard SMA coaxial connectors.     

硫系玻璃在长波红外无热化连续变焦广角镜头设计中的应用

针对市场上现有红外广角镜头大多采用定焦结构且缺乏无热化设计的现状,根据光学变焦系统的设计原理,设计了一种有效焦距范围为10~24 mm（变倍比为2.4:1）、视场角变化范围为34~90、工作波段为8~12 m、F/#为2.8的无热化连续变焦广角镜头。考虑到红外镜头多用在温度变化较大的使用环境中,系统设计选用了硫系玻璃NBU-IR2（Ge20Sb15Se65）以及常规红外材料锗（Ge）和硫化锌（ZnS）制备的六片镜片,通过合理分配各个镜片的光焦度及其空气间隔等参数,在连续变焦设计的基础上实现了无热化的光学设计效果。实验结果显示,系统在-40~60℃的温度范围内均可实现品质良好的红外热成像效果,调制传递函数全视场范围内均大于0.25。系统结构较为紧凑简单、质量较轻,仅在一片硫系玻璃镜片上设计了一处非球面,可有效控制光学系统的加工成本。整体设计适用于车载夜视等应用领域。     

A quantitative study of Luneberg-lens reflectors

Luneberg-lens reflectors, which provide passive wideband and wide-angle radar-signature augmentation, have been widely used in small military target drones, decoys, and marine vessels. Due to the difficulty of fabricating inhomogeneous dielectrics with a continuously varying index, Luneberg lenses are usually constructed with multilayered step-index dielectrics. This paper presents a quantitative study of a practical design of a three-layer Luneberg-lens reflector for C- and X-band operations. Extensive wideband and wide-angle measurements were carried out for this lens with three different cap reflectors, as well as for the lens alone without any reflector. A comprehensive numerical analysis, using the finite-element method combined with boundary integral equations, was also conducted. This was done to support the measured data and to provide additional insight for a better understanding of the performance and the limitations of the Luneberg-lens reflector than could be achieved with the traditional ray-optics method. The effect of reflector size is discussed, and the limitation of three-layer design is demonstrated. It has also been shown that very accurate material parameters must be ascertained so as to achieve the level of accuracy commonly desired in the computational electromagnetic codes applied to inhomogeneous dielectrics. The excellent agreement between the numerical and measured data indicates that this full-wave Maxwell solver can be used to explore the design limits and optimize designs for this type of lens reflector.     

Procedure for correct refocusing of the Rotman lens according toSnell's law

A procedure is derived for proper refocusing of a dielectric-filled Rotman lens with beam port locations determined according to Snell's law. The theoretical performance of such a lens is compared with that of a conventional design at wide scan angle and the design equations for correct refocusing of the refracting lens derived. The approach provides an alternative lens configuration which may give a wider field of scan, at a given focal length, for lenses fabricated in microstrip or stripline. The presence of grating lobes in the lens is discussed     

利用相移条纹相位解调的广角镜头畸变校正

文中提出了一种基于相移条纹图相位分析的广角镜头畸变校正方法。首先,用大尺寸液晶平板显示器显示四幅相移量为π/2的余弦条纹图作为校正模板。然后,用广角镜头相机拍摄该校正模板,获得四幅畸变条纹图,使用四步相移算法解调径向畸变条纹图的相位分布。由于经广角镜头成像的图像中心区域几乎无畸变,利用图像中心无畸变的相位值进行数值拟合得到径向无畸变条纹图的相位分布,作为求解径向畸变相位的基准,也就是径向畸变相位分布可以根据径向畸变条纹图的相位分布与径向无畸变条纹图相位分布相减得到,再将畸变相位转换成实际的畸变量。提出的方法不需要通过特征点或特征线确定畸变模型,可以直接计算畸变图像中每个像素点的畸变量。实验结果表明,提出的方法简单、有效,具有广泛应用价值。     

Performance of probe-fed microstrip-patch element phased arrays

The performance trends for large phased arrays with probe-fed microstrip-patch elements are discussed, with primary consideration given to single-probe (unbalanced) feed for rectangular grid arrays with rectangular patch geometry. The effects of substrate thickness and permittivity, patch dimensions, and element spacing are examined. Pronounced surface- and leaky-wave effects that tend to limit the scan volume are found. Interaction between the patch resonance at broadside scan and the leaky-wave resonances leads to an E-plane scan-bandwidth tradeoff. In the H-plane scan a transverse electric (TE)-type guided wave resonance is found that becomes pronounced when the H-plane dimension is a large fraction of the H-plane element spacing. This leads to a limitation of the H-plane patch dimension in the rectangular grid arrays. An element design procedure is proposed and illustrated for an element suitable for wide-angle scan over a ±5% frequency band     

Optimum optical limited scan antenna

An optical limited scan antenna system is considered for applications such as spot coverage of a small portion of the earth from a satellite. The optimum criterion relating aperture efficiency, number of control elements, and angular coverage is revisited briefly. The optical scheme advocated utilizes a bootlace aperture lens, a generalized Luneberg lens focused to the near field, and a small array of active elements. The operation of the system is described first in terms of geometrical optics and elementary diffraction principles. The subarray viewpoint is then developed using simplified diffraction concepts. These results form the basis of a design procedure for the synthesis of high performance limited scan systems. An accurate solution necessary for the analysis of small antennas is developed using a modal decomposition and the wave equation. Numerical computations for a case of practical interest verify the expectation of near optimum performance.     

Multibeam antennas with polarization and angle diversity

A 10-GHz discrete cylindrical lens array with multiple beams is designed and characterized as a receiving angle-diversity array for wireless communications in a multipath environment. The array also has dual-orthogonal polarization and therefore built-in polarization diversity. The array is designed for wide-angle scanning between -45° and 45° and measured scanning patterns are presented. The polarization isolation between the two channels is about 30 dB at boresite and about 10 dB for a 30° scan angle. The addition of the lens array at the very front end of a link shows significant reduction of multipath fading peak-to-null ratio     

A VLSI Implementation of Barrel Distortion Correction for Wide-Angle Camera Images

Wide-angle cameras are widely used in surveillance and medical imaging applications nowadays. Images captured by wide-angle lens suffer from barrel distortion which means that the outer regions of the image are compressed more than the inner one. A low-cost high-speed VLSI implementation for barrel distortion correction is presented in this brief. In our simulation, the proposed circuit can achieve 200 MHz with 45 K gate counts by using TSMC 0.18 $mu{hbox {m}}$ technology. Compared with the previous distortion correction design, our circuit requires less hardware cost and achieves faster working speed.      

一种基于压控移相技术的低成本相扫天线

研制了一种基于铁电体压控移相技术的低成本相扫天线阵列,该天线采用空间馈电透镜型式,省去复杂的馈电网络,减少移相器/TR组件数量,能显著降低相控阵天线的制造成本。介绍了空馈铁电体透镜相控阵天线系统的组成及其特点。对透镜天线关键部件的设计作了详细阐述,给出了12列铁电体空馈透镜天线阵列的实验结果,结果表明:在X波段,研制的铁电体透镜天线阵列在10%频带内可实现天线波束±45°的电控扫描,各扫描状态的输入驻波比小于1.4。     

共轴双反射光学天线系统的优化设计

本文介绍一个共轴光学天线系统的计算机自动优化设计软件,此软件可使设计者方便、快速地设计各种优化的共轴双反射镜系统。     

Design trades for Rotman lenses

The foundation of a satisfactory Rotman lens design is geometric. The effects of seven design parameters (focal angle, focal ratio, beam angle ratio, maximum beam angle, beam port curve ellipticity, array element spacing, and focal length/λ) on the shape, and on the geometric phase and amplitude errors of a Rotman lens are described. The advantage of beam port shaping to reduce phase error, and of pointing port horns at the opposite apex (instead of normal to the curve) to reduce off-axis beam amplitude asymmetries, are shown numerically. A design procedure for selecting these parameters is given, and a calculation of lens gain is presented     

基于V型谐振腔的热稳定性分析

为了提高V型谐振腔的热稳定性,采用了图解分析法,将V型折叠腔等效为腔内含有一个透镜的共轴球面腔。同时考虑到晶体热透镜效应,结合多元件光学谐振腔的等价腔分析法,将等效后腔内含透镜组的多元件球面腔近似等价为腔内不含透镜的共轴球面空腔。对V型腔等价后的共轴球面空腔的稳定性进行了理论计算和仿真分析。结果表明,当总腔长为75mm、折叠角为0.15π左右时,谐振腔具有最宽的热稳定范围;此时若增益介质与折叠镜的间距为28mm,则谐振腔能适应的最小热透镜焦距可达12mm。这一结果体现了谐振腔关键参量对热稳定性的重要影响,对激光腔型稳定性的优化设计具有一定的指导意义。     

Analysis of phased array lenses

An equivalent network representation of a feedthrough lens array, which takes into account mutual coupling between the array elements, is presented. The model is employed to predict performance characteristics, which include element mismatch, peak voltage loading of the phase shifters, element currents, and transmitted power. Both analog and digital phase shifters are treated in the analysis. It is shown that, irrespective of the type of phase shifter, the mismatch from element to element at a fixed scan angle is not identical. This variation is explained in terms of the multiple reflections that take place between the two surfaces of the lens. Further, as a function of scan angle, the element mismatch for a digitally phased array lens does not vary in a smooth manner but exhibits a decided ripple.     

An Optimum Current Mirror Ratio for Low Phase Noise LC–VCO

A design technique for a low phase noise inductor- capacitor voltage-controlled oscillator (VCO) using an optimum current ratio between the oscillating core and the bias circuit is proposed. Conventionally, it is preferred that the current in the oscillating core is maximized to reduce the phase noise. In this letter, however, we find that an optimum current ratio exists for low phase noise for a given power budget. To find the optimum ratio, a theoretical analysis is performed and verified by a prototype VCO using a 0.13 $mu{rm m}$ CMOS process. Based on the analysis and the measured data, the optimum ratio is shown to be 2 $sim$ 3.      

Coaxial feeds for high aperture efficiency and low spillover of paraboloidal reflector antennas

Coaxial feeds produce an approximate sector-shaped pattern, an almost optimum pattern of a feed for high aperture efficiency and low spillover of paraboloid antennas. Such a coaxial feed consists of a central circular waveguide which is surrounded by one or more conductors with circular cross sections. Theoretical and experimental investigations on coaxial feeds excited by H11modes have shown that the first ring yields the highest increase in the aperture efficiency of paraboloid antennas illuminated by them. Measurements performed on paraboloid antennas illuminated by a coaxial feed with only one ring yielded aperture efficiencies of 68 to 75 percent for angular apertures of the paraboloidal reflector of100degto160deg. Circularly symmetric patterns in conjunction with almost linearly polarized aperture fields can be achieved by multimode coaxial feeds. The values for the aperture efficiency, which are calculated for paraboloid antennas illuminated by multimode coaxial feeds, nearly reach the theoretical optimum. The measured values are 68 to 80 percent. In addition, the multimode feeds produce very little cross polarization.     

Design of Rotman lens for beamsteering of 94 GHz antenna array

The design and development of a Rotman lens for operation at 94 GHz which feeds an antenna array for beamsteering applications is presented. The construction is completely realised in waveguide technology. The lens consists of 15 beam ports covering a scan range of /spl plusmn/23.3/spl deg/ in steps of 3.3/spl deg/ and 10 array ports connected via phase compensating transmission lines to a linear antenna array. Experimental results are compared with theoretical calculations.