Phase scanning of one-dimensional pattern

A method of determination of phase function required for scanning a one-dimensional pattern is presented. Analysis reveals that the one-dimensional pattern is produced in the meridian plane of a two-dimensional aperture by application of nonlinear phase in the directions along and parallel to this plane. Scanning is produced by application of a linear phase progression in the perpendicular direction. The slope of the linear phase progression is different for different positions along the direction of nonlinear phase distribution. Expressions giving the variation of this slope along the length of the array for various amplitude distributions and desired radiation patterns are derived.     

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。     

Scanning of cosecant beams generated by a tilted planar array ofnonisotropic radiators

A method of scanning a one-dimensional shaped pattern generated by a tilted circular planar array of nonisotropic elements is presented. A method of synthesis of phase function for a desired cosecant pattern and specified amplitude distribution for excitation of the elements of the array is presented. The phase distribution required in the perpendicular direction for retaining the beam shape in the scanned plane is determined. Computed results on the phase distribution and radiation pattern are presented. The appropriate correction is applied to get a better agreement between the realized and desired patterns in this scanned position of the beam     

Circular aperture pattern synthesis from collapsed equivalent line-source distributions

A novel circular aperture pattern synthesis technique is presented, which enables a linear line-source distribution to be converted to a rotationally symmetric circular aperture distribution, of which any /spl phi/-cut radiation pattern is ideally the same as the principal plane pattern of the line-source distribution. Line-source pattern synthesis techniques are numerous and versatile and the technique presented here allows these techniques to be applied to circular apertures as well. This new synthesis method is most compatible with line-source distributions which have zero edge illumination.     

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.     

Traveling wave arrays of mismatched elements

Normal design practice for traveling wave arrays assumes that radiating elements cause negligible mismatch to the transmission line feed. This assumption cannot be made for tightly coupled or largely reactive radiating elements. An analysis is given for calculating element resistances and spacings which will produce an aperture distribution with the desired amplitude and linear phase in the presence of internal multiple reflections along the transmission line. The method leads in general to variable element spacing. Two examples of arrays designed on this basis are given.     

Phase synthesis of antennas for a given radiation pattern in oneplane using piecewise linear aperture phase distribution

A phase-only method for the synthesis of planar aperture antennas for a given complex radiation pattern in one plane is reported. The problem is reduced to determining an appropriate aperture phase distribution in the form of a ruled function and solved for apertures with rectangular shape and an arbitrary amplitude distribution and for apertures of arbitrary shape and amplitude distribution. This method can be used for controlling the pattern of phased-array antennas. Results of computer modeling are presented     

隙缝馈电平面阵天线

正 (一)基本要求 合成孔径雷达原理样机需要一部工作在X波段,发射水平极化波的扇形波束天线。天线的波束宽度沿飞机航向(E平面)约1,垂直于航向(H平面)为9,增益为30 dB;或在H平面上于11的波束宽度内,将波束赋形为CSC2()为波束宽度),增益为27dB。天线的结构要适于作侧视安装。 (二)方案选择 满足以上条件的天线方案有三类:(1)以线阵作照射器,柱形抛物面作反射器的复合天线;(2)以线阵作辐射器,外加有一定张角的两块板构成线阵喇叭形天线;(3)平面     

Theory of the directional pattern of a pyramidal horn

A method is presented for calculating the directional pattern of a pyramidal horn antenna from first principles by diffraction theory. It is based on first finding the field in the plane of the aperture, both inside and outside the physical aperture. This is then transformed to find the far-field pattern. The field in the aperture plane is made up of contributions from the primary wave reaching the aperture, whose phase surfaces are assumed to be spherical, edge waves propagating in the plane of the apertures and edge waves that have been reflected from inside the horn. The edge waves traveling in the plane of the aperture are the main object of interest. They propagate not only perpendicular to the edges, but also diffract parallel to the edges because of the finite length of the edges. By taking this fully into account, a directional pattern over the whole forward hemisphere can be predicted for any given frequency from the geometry of the horn. For a particular horn the principal cuts agree with direct measurements made at the National Physical Laboratory, Teddington, UK, to within about 4 dB (except near deep minima)     

表面误差对反射面天线电性能的影响

 针对反射面天线存在的误差问题,建立了包含系统误差和随机误差对电性能影响的数学模型.该模型根据表面误差与口径面相位分布的关系,利用口径法得到功率方向图.通过对模型分析可知,随机误差对方向图各个方位产生影响;系统误差产生栅瓣,且栅瓣的位置和电平取决于变形情况.最后将模型应用到8米口径的抛物面天线中,收到了满意的结果,验证了文中模型和方法的正确性.     

Design of line-source antennas for sum patterns with sidelobes of individually arbitrary heights

A design method is presented for the determination of continuous line sources which will yield sum patterns consisting of a narrow main beam and sidelobes whose individual heights can be adjusted to any arbitrary specification. The method is based on a generalized Taylor pattern which is perturbed in successive iterations until the desired pattern results. For practical cases the convergence is rapid, and an economical computer program of general applicability has been written which will terminate when the desired pattern has been achieved within a specified tolerance, at which point a final pattern and aperture distribution are printed out. The theory is illustrated by several cases of practical interest.     

基于阿基米德螺线的稀布面阵综合方法

提出一种基于改进遗传算法的稀布面阵综合的新方法。该方法通过对阿基米德螺线参数的合理设置,确保了阵元在沿阿基米德螺线的轨迹分布时依然能够满足阵元数约束、孔径约束和最小阵元间距约束,从而将稀布面阵的优化问题转化为非对称线性阵列的稀布问题,这就大大降低了问题的复杂程度。仿真实验结果证明了该方法的有效性。     

Synthesis of offset dual reflector antennas transforming a given feed illumination pattern into a specified aperture distribution

The problem of transforming a given primary feed pattern into a desired aperture field distribution through two reflections by an offset dual reflector system is investigated using the concepts of geometrical optics. A numerically rigorous solution for the reflector surfaces is developed which realizes an exact aperture phase distribution and an aperture amplitude distribution that is accurate to within an arbitrarily small numerical tolerance. However, this procedure does not always yield a smooth solution, i.e., the reflector surfaces thus realized may not be continuous or their slopes may vary too rapidly. In the event of nonexistence of a numerically rigorous smooth solution, an approximate solution that enforces the smoothness of the reflector surfaces can be obtained. In the approximate solution, only the requirement for the aperture amplitude distribution is relaxed, and the condition on the aperture phase distribution is continued to be satisfied exactly.     

Efficient and accurate method for calculating and representingpower density in the near zone of microwave antennas

A method for computing and exhibiting Fresnel-region fields radiated by microwave antennas that uses plane-wave scattering matrix analysis is presented. Near-fields are calculated by numerically integrating the complex far-field antenna pattern. The predicted near fields are exhibited as relative power density contours lying in a longitudinal plane bisecting the antenna's aperture. With spatial-coordinate scaling, each set of contours becomes a function of the relative aperture distribution and the electrical size of the antenna. If the electrical diameter is much larger than any normalized transverse coordinate of interest, the contour set becomes invariant with respect to antenna size. The coordinate normalization can produce contours applicable to any antenna with the same relative aperture distribution, regardless of antenna size     

An improved thinning method for density tapering of planar array antennas

A thinning method is presented to realize the desired aperture distribution in a planar array antenna with elements fixed on an array lattice. In this method elements to be excited are determined by quantizing cumulative weights which are calculated from the desired aperture distribution. At first, this method is applied to density tapering on orthogonal axes of a planar array. Radiation patterns of the planar array determined by this method are compared with those by the desired amplitude distribution, and the results show good coincidence. Next, this method is extended to density tapering on four axes, that is, orthogonal and diagonal axes of a planar array. Moreover, this method is applied to density tapering with multi-amplitude level elements in order to enhance directive gain of thinned array. Lastly, a rectangular planar array was fabricated, and its radiation patterns were measured. Measured results were in good coincidence with calculated ones, and the usefulness of this method was verified.     

A synthesis procedure for coated reflector antennas

A procedure is presented for the synthesis of coated axially symmetric reflector antennas to provide specified far-field radiation patterns. The technique stems from ray tracing from the feed to the aperture plane via reflection from the reflector surface. The coating profile required to attenuate the aperture fields is determined based on the reflection of plane waves from metal-backed slabs. The procedure involves two steps. Initially the thickness required to produce the proper magnitude aperture distribution is obtained. Then the reflector is shaped to adjust the phase across the aperture. This procedure is demonstrated in the design of a -40 dB Taylor pattern. Comparison of the results with those obtained using a moment method formulation revealed good agreement between the two formulations     

Generating a plane wave with a linear array of line sources

Creating a plane wave across an antenna under test is important for accurate antenna measurements. This paper optimizes the location and weightings of an array of line sources in order to approximate a plane wave at a given location in space. The amplitude and phase ripples across a desired test aperture are optimized to be much less than that of a uniform array with the same number of elements. Results are presented for a nine-element array with optimized amplitude and phase weights, with optimized weights and spacing in the x-direction, and with optimized weights and spacing in the x and z directions. The optimized approximate plane wave is a significant improvement over a uniform array or a single line source.     

Scattering from apertures in infinite ground planes using FDTD

A scattered field version of FDTD for scattering from an aperture in an infinite ground plane is presented. In this formulation the fields reflected from the infinite ground plane are computed analytically, not as FDTD scattered fields. This is necessary to eliminate scattering from the edges of the ground plane, where it is terminated at the FDTD outer boundary. Also, the fields scattered by the ground plane are usually of much higher amplitude than the desired aperture-scattered fields. In this formulation these fields need not be absorbed by the FDTD outer boundary. This provides more accurate calculation of low amplitude scattering from the aperture. The formulation can include materials in the aperture and on both sides of the infinite ground plane. For example, scattering from an aperture antenna with a dielectric cover backed by an aperture filled with lossy dielectric can be computed with this formulation     

Circularly polarized feed for cylindrical parabolic reflector antennas

The feed design described is a linear array of crossed dipoles above a ground plane. The radiation patterns of the longitudinal and the transverse dipoles are made equal by parallel longitudinal rods, referred to as beam forming rods or beam matching rods. When used as a circularly polarized feed for an offset parabolic cylinder antenna, aperture efficiencies (spillover included) as high as 0.89 are potentially available if the field distribution along the array is uniform. The beam patterns of the feed were computed both by the method of moments and the geometrical theory of diffraction and are compared with patterns measured on a model at 1.5 GHz. A method of matching the impedance for both linear polarizations is proposed using parallel impedance matching rods.     

Radiation pattern of a test reflector antenna from near-fieldmeasurements over focal region of a coupled lens or offsetreflector

A novel scheme has been investigated by which the radiation pattern of a test reflector antenna is determined by rescaling a plot of the electric field distribution in the focal plane of a large lens or in the offset focal plane of a large offset reflector placed in front of the transmitting antenna under test. The major advantage of the technique is that it permits a direct plot of the desired radiation pattern from near-field amplitude data without requiring any phase measurements. The test method is simpler and the test data more accurate than for pervious test methods