Radiation pattern synthesis for circular aperture horn antennas

A set of radiation pattern functions, suitable for synthesis of radiation patterns from circular aperture horn antennas, is obtained by assuming an aperture distribution consisting of the fields of cylindrical waveguide modes. A technique is presented for using a linear combination of the radiation pattern functions to approximate a desired radiation pattern. Linear combinations of the radiation pattern functions resulting in maximum secondary gain, when used to illuminate a paraboloidal antenna, are obtained empirically. Using spherical wave theory, maximum performance theoretically obtainable from an antenna is derived as a function of the aperture size of the feed system; the feed efficiency resulting from these theoretical limits on performance is compared to the feed efficiency of patterns obtainable from circular aperture horn antennas, and to experimental results of attempts to realize optimum circular aperture horn patterns.     

基于泰勒分布线阵特殊旁瓣技术的研究

提出了基于泰勒加权分布线阵特殊旁瓣要求的设计方法,其波束图是由给定的旁瓣级要求来设计的泰勒分布波束图,在实际需要的特殊旁瓣要求上,设计满足了要求的最窄波束宽度波束图。给出了相应的参数设计,并证明该设计能在要求的最大旁瓣级上获得最大阵增益。借助计算机对线阵进行波束图设计。结果表明,使用该方法设计的波束图能满足特殊旁瓣要求和最大阵增益。     

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.     

Analysis and synthesis of axial field patterns of focused apertures

It is shown that the axial field pattern of an aperture focused in the Fresnel region can be synthesized in the same manner as the angular pattern of an aperture in the Fraunhofer region. The aperture distribution which achieves a specified axial pattern is related to the aperture distribution of the specified pattern in the far field through a simple variable transformation. Therefore all analysis and synthesis techniques for far-field patterns can be applied to Fresnel region axial patterns of focused apertures.     

Design of planar arrays to obtain efficient footprint patterns withan arbitrary footprint boundary

An antenna pattern synthesis technique is presented that permits the design of planar antenna arrays with footprint patterns of a specified boundary. This technique is applicable to planar arrays of a wide variety of grid structures and can produce patterns with controlled ripple and sidelobe levels. The approach involves two steps: the first consists in stretching the pure real-continuous aperture (an extension of circular Taylor distributions, developed by Elliott and Stern [1990]) into a distribution with a boundary that is inversely proportional to the flat-top beamwidth; the second is the minimization of a cost function (the square of the difference between the resulting power pattern and the desired one) using the Fletcher-Powell method. A square footprint, produced by a rectangular grid (obtained by sampling this distribution) with the corner elements appropriately removed, is presented as an illustration of the method     

A one-parameter circular aperture distribution with narrow beamwidth and low sidelobes

A one-parameter circular aperture distribution is developed which provides an optimum compromise between narrow beamwidth, low sidelobes, and low apertureQ. The pattern is a modifiedJ_{1}(x)/x, analogous to the Taylor one-parameter modified sin(x)/xline source distribution. Sidelobe envelope taper is essentially that of a uniformly excited circular aperture; hence the aperture is lowQ. The aperture distribution which is rotationally symmetric is given by a modified Bessel function of zero order. Like all high efficiency distributions, it has a pedestal. All antenna quantities, sidelobe ratio, beamwidth, aperture efficiency, and edge taper, are uniquely related to the parameterH. A table of these quantities is given for sidelobe ratios up to 50 dB. A typical pattern and several distributions are graphed. This new distribution allows tradeoff studies to be made against any design quantity, with all other quantities determined through the one-parameter.     

Synthesis of multireflector antennas by kinematic and dynamic raytracing

A technique for synthesizing reflector surfaces that transform a known input ray-field (e.g., the radiation field of a feed) to a desired output ray-field (e.g. an aperture distribution) is presented. The synthesis problem is reduced to solving linear equations by local biparabolic expansions of the reflector surfaces. Because the solution is easier to control, this is advantageous compared to existing techniques based on solving nonlinear differential equations. The condition to obtain low cross polarization can therefore be readily included, and the requirements for an exact solution to exist can be found clearly. The latter has been the subject of discussion in the literature for several years. The synthesis technique is applied to a shaped-offset dual-reflector antenna and to the proposed dual-reflector feed of the spherical reflector antenna in Arecibo. In both cases circular and elliptical apertures are considered     

椭圆口径天线的一种新的设计方法

利用口径坐标变换，比较了圆口径和椭圆口径天线方向函数的差异，得出了将圆口径分布方向图特性映射到椭圆口径的条件，并将圆口径天线最佳综合方法圆Taylor综合应用于椭圆口径天线的设计。将这一条件应用于椭圆离散阵设计，给出了设计实例，比较了连续圆口径分布与椭圆离散阵的特性，扩展了椭圆阵列的常规设计方法。     

Optimum aperture monopulse excitations

A unified formulation of the optimization of monopulse antenna performance indices for a specified sidelobe envelope function and/or specified nulls of the pattern is presented. The performance indices considered are beam efficiency, gain factor, and angular sensitivity factor of rectangular and circular apertures. The unconstrained optimization of beam efficiency result in an integral equation, the solutions of which are prolate spheroidal wave functions for rectangular aperture and hyperspheroidal wave functions for circular aperture. These functions reduce, respectively, to Legendre and Zernike polynomials in the case of gain factor and angular sensitivity factor. The double orthogonality properties of these eigenfunctions are used for constrained optimization. The results obtained by this technique for the near-in sidelobes constrained at a uniform level are shown to be in agreement with the earlier works. The method is applicable for other aperture surfaces such as elliptical, ellipsoidal, and spherical.     

Synthesis of the antenna pattern for a radiating slot in a metal cylinder

The synthesis of a prescribed far-field pattern by means of a radiating slot in a perfectly conducting infinite circular cylinder is considered. The narrow circumferential slot and the infinite axial slot are studied in detail. In either case, the problem is to find the distribution of the electromagnetic field in the aperture that yields a radiation pattern that is the best mean-square approximation to a given pattern, under certain constraints. Various quality factors for cylindrical modes are discussed, and a detailed comparison with the synthesis problem for a planar aperture is performed. It turns out that Rhodes' synthesis method has no equivalent in the cylindrical case, and that the best admissible mean-square approximation to a given pattern may be a very poor approximation in amplitude. However, an iteration scheme is developed in which the phase approximation is sacrificed for the sake of substantially improving the amplitude approximation. Numerical results based on such a scheme are displayed, for prescribed omnidirectional and sectoral patterns.     

Scanning of sector and cosecant beams generated by a circular aperture

A method of scanning a one-dimensional shaped pattern generated by a circular aperture is presented. It is shown that the desired beam shape can be retained in the desired scan plane by superposing on the nonlinear phase distribution applied along and parallel to the meridian plane, a linear phase progression along the perpendicular direction. Analysis carried out using the stationary phase method of evaluating the integral reveals that the gradient of the linear phase progression is a function of position along the meridian plane of the aperture. Expressions for the phase functions are derived. Computed results on the phase distribution and the radiation pattern are presented.     

Arbitrary footprint patterns obtained by circular apertures

The proposed quasi-analytical method undertakes the shaping of a desired footprint as a composition of several /spl phi/-symmetric circular Taylor patterns exhibiting flat-topped beams. The final pattern is obtained after sampling the obtained circular aperture for circular grid planar arrays. A square and a rectangular footprint pattern, both radiated by a planar array with 1246 elements, demonstrate the performance of the technique.     

航管二次雷达发射天线方向图综合

该文介绍航管二次雷达(SSR)发射天线方向图综合的新方法,这种方法以有源相控阵天线为基础。利用带底座的Cosine口径幅度分布综合出所需的定向方向图,辐射用于询问的P1和P3脉冲。在上述口径幅度分布基础上,利用驻相法获得所需的口径相位分布以综合出方位上全向的方向图,辐射用于询问旁瓣抑制(ISLS)的P2脉冲。省去了单独辐射P2脉冲的天线和相应设备。     

Synthesis of amplitude-phase distribution and shape of a planarantenna aperture for a given power pattern

The problem of synthesis of an optimum shape of a planar aperture and optimum amplitude-phase distribution over this aperture corresponding to a given power pattern is considered. The functional, which ensures minimization of the mean-square deflection of the magnitudes of the given pattern and of the synthesized one in the area of the main lobe and minimization of the sidelobes, is used as the optimization criterion. The problem of determination of the optimum functions of the shape or a planar aperture and of the excitation over this aperture is reduced to the determination of solution of the system of two nonlinear integral equations. The numerical algorithms of solution of these equations are based on utilization of the method of successive approximations and the Newton-Kantorovich method. The numerical results of synthesis of partial power patterns with rectangular and triangular outlines are presented     

基于量子微粒群的综合孔径圆环阵排列方法

稀疏天线阵列设计是综合孔径微波辐射计的一个重要研究内容。圆环阵因其可实现(u,v)平面基线零冗余、结构简单以及共形、波束旋转对称等特点而备受关注。针对均匀圆环阵UV覆盖不均匀的问题,提出基于量子微粒群优化(QPSO)的综合孔径圆环阵排列方法,以改善圆环阵的UV覆盖。该方法引入量子行为的搜索机制,并设计一种新的圆环阵优化目标函数;与现有方法相比,该方法在提高全局搜索效率的同时,大大降低计算复杂度,且能更好地度量圆环阵UV覆盖的均匀程度。数值仿真结果验证了本文方法的有效性。     

Coarray synthesis with circular and elliptical boundary arrays

An elliptical boundary aperture is a collection of points lying on an ellipse from which energy is transmitted and/or received. An important special case is the circular boundary aperture. When these apertures are used with beamforming to produce a narrowband image of a far-field source, the corresponding point spread function (PSF) is characterized by high sidelobes. The concept of the coarray of an imaging system is used here to develop techniques which synthesize the effect of a more desirable PSF with an elliptical boundary aperture. Techniques are given for use in active imaging of spatially coherent sources, as well as passive imaging of spatially incoherent sources. Discrete arrays and continuous apertures are considered separately. The approach shows that the PSF synthesis problem can be solved in many more ways than previously recognized, and this fact is exploited to develop procedures which have a least-squares optimality property.     

Near Field Analysis of the Modal Scattering at Radiating Apertures

A rigorous method for the determination of the modal scattering at radiating apertures is presented. Near-field boundary conditions to be satisfied on the outer surface of the conducting structure containing the aperture (e.g. a horn antenna) are completely taken into account. The resulting scattering matrix of the radiating aperture can be integrated into any mode-matching technique as a termination for the cascaded structure commonly used to match the aperture to the exciting waveguide. The method is based on a multiple-multipole expansion of the electromagnetic field outside the radiating object in conjunction with a point-matching technique. Horn antennas with elliptical and circular apertures have been analyzed using the suggested method. Excellent agreement with measurement results has been achieved for both the radiation pattern and the aperture scattering parameters.     

The unifying role of the coarray in aperture synthesis for coherentand incoherent imaging

Systems of two-dimensional (2-D) imaging arrays and apertures are considered from the point of view of their performance in the imaging of spatially incoherent as well as coherent source distributions. Such systems find applications in radar, sonar, and ultrasound imaging, as well as in applications such as seismology and radio astronomy. For linear imaging techniques related to beamforming and based on the Fourier transform relationship between the source distribution and the aperture plane measurements, the point spread function of the system completely characterizes its performance. This function is determined by the geometry of the physical aperture or array as well as the weighting that can be applied to measurements. It is shown that the introduction of the concept of coarray, both for receive apertures in incoherent imaging and for transmit/receive systems in reflection-mode coherent imaging, provides a convenient and elegant framework within which many apparently isolated techniques for point-spread function or aperture synthesis can be understood. In addition to this unifying role, coarray concept gives new insight into the aperture synthesis process, which allows interesting new imaging techniques to be developed, especially in coherent imaging     

Synthesis of shaped line-source antenna beams using pure realdistributions

Shaped line-source antenna beams can be synthesised by introducing complex roots in a Taylor line source distribution to achieve null filling in the shaped region. Optimisation of these roots and others allows individual control of the amplitude of ripples and the heights of unshaped sidelobes up to any specified order. The corresponding continuous aperture distribution can be made pure real by appropriate root-pairing, which makes the results applicable, via sampling, to resonantly spaced linear arrays     

A radiometric antenna gain calibration method

A radiometric method is presented for measuring the power gain of a microwave antenna. It is particularly applicable to horns with gains in the range 20-45 dB, and an absolute uncertainty (3sigma) of less than 0.1 dB is achievable in favorable cases. An absorbing screen with a circular aperture is placed in the far-field of the test antenna. The diameter of the aperture is chosen to subtend an angle much smaller than the main lobe of the radiation pattern of the test antenna. Then two sheets of microwave absorber (one at ambient temperature and the other cooled to the boiling point of liquid nitrogen) are alternately placed first behind the screen aperture and then, for normalization, across the aperture of the test horn. The ratio of the antenna temperature differences measured with a sensitive microwave radiometer is proportional to the effective antenna solid angle, and thus its directivity. Corrections must be applied for near-field effects, diffraction at the screen aperture, partial resolution of the screen aperture by the main lobe of the test antenna pattern, and ohmic losses. A comparison of black disk measurements using a large conical horn at 86 GHz with theoretical calculations confirms the accuracy of this gain calibration technique.