The cylindrical antenna as a probe for studying the electrical properties of media

When a base-driven cylindrical monopole (or center-driven dipole) is immersed in an arbitrary medium, the electric and magnetic fields on its surface depend not only on its length and radius but also on the effective conductivity and permittivity of the medium. These fields can be explored and measured with small probes designed to travel along the cylindrical surface of the antenna. The interpretation of the observations depends on the availability of a general theory that correctly describes the distributions of current and charge on the conductor. The results of a new theory that is valid for electrically thin monopoles up to5lambda/8(dipoles up to5lambda/4)in length over all practical ranges of conductivity and permittivity of the ambient medium, including those characteristics of under- and overdense cold plasmas, are described together with their experimental verification.     

宽频带粗振子平板反射器阵列天线技术研究

采用Hall6n积分方程分析了粗振子阵列天线的驻波特性,以及反射板尺寸变化对增益、前后比的影响,给出了一种垂直极化工作、水平面主波束约105°的二单元宽带粗振子阵列天线的优化设计实例。在一个倍频程内,天线增益不小于11dBi,电压驻波比小于2,前后比大于22dB。曲线图和数据表对于粗振子阵列天线优化设计具有一定的参考价值。     

Effect of the imperfect flat Earth on the vertically polarizedradiation of a cylindrical reflector antenna

The radiation of a circular cylindrical reflector antenna in the presence of imperfect flat Earth is treated in an accurate manner. The boundary value problem is formulated in terms of a full-wave integral equation converted to the dual-series equations and then regularized by using analytical inversion of the static part. The resulting Fredholm second-kind matrix equation is solved numerically with guaranteed accuracy. The feed directivity is included in the analysis by using the complex source-point method. Various antenna features, which include the overall directivity, efficiency, gain, and radiated and absorbed power fractions have been calculated and compared with the free-space antenna characteristics. They show some phenomena not predicted by approximate techniques     

菲涅尔区修正圆柱面天线的聚焦场特性

在圆柱面上进行一维菲涅尔区相位修正结构设计,可以构成一类新型的点源馈电透镜天线。该文用辅助源法导出该透镜天线对任意斜入射平面波形成的聚焦场分布,分析了其聚焦性能及偏轴扫描特性。     

Radiation characteristics of an infinite dielectric-coated axiallyslotted cylindrical antenna partly embedded in a ground plane

The radiation characteristics of an axial slot on a dielectric-coated conducting circular cylinder embedded in a semi-circle in an infinite ground plane (GP) are examined. The boundary-value method is employed to obtain the solution with the aid of the partial orthogonality of the trigonometric functions. The resulting dual infinite series involved in the solution is then truncated to generate numerical results. The geometry considered here is important because it can be implemented on the body of any mobile communication system. Moreover the GP adds a new parameter to the slotted dielectric-coated conducting circular cylindrical antenna and can be used in beam shaping and to enhance the antenna performance     

On scattering of the fields of cylindrical and plane waves by compact lossy-metamaterial structuress

The article presents a rigorous solution to the problem of scattering of a cylindrical (or plane) wave by cylindrical metamaterial structures of various geometries. Negative refraction of a plane wave is shown, and total internal reflection for such structures is studied. Masking of a perfectly conducting cylinder placed in a metamaterial cylinder in the geometric-optics shadow is demonstrated.     

Subtraction of edge-diffracted fields in antenna radiation patterns for simulation of infinite ground plane

A measurement technique is introduced to simulate the radiation pattern of an antenna mounted on an infinite sized ground plane. The edge diffracted fields from a finite ground plane are measured and then subtracted from the total field to yield only the direct radiation from the antenna that would be present if the antenna were mounted on an infinitely large ground plane. Comparisons with theory are also presented.<>     

Broadband probe-fed patch antenna with a W-shaped ground plane

A new design of a broadband probe-fed patch antenna with a W-shaped ground plane is presented. The W-shaped ground plane is obtained by bending the conventional planar ground plane into an inverted V-shape, seen in the resonant direction of the patch antenna and then adding proper flanges at the two straight edges of the bent ground plane. The proposed design is applicable to the patch antenna with a planar radiating patch with a thin air substrate. With the use of the proposed W-shaped ground plane, the required probe-pin length in the substrate remains small, although the effective substrate thickness is significantly increased, resulting in a much wider operating bandwidth. Also, by choosing proper dimensions of the W-shaped ground plane, the antenna gain for frequencies over the obtained wide bandwidth is enhanced, compared to the conventional patch antenna with a planar ground plane. In addition, the cross polarization is also reduced for the proposed design and the cross-polarization level (XPL) in the H-plane pattern can even be better than that of a conventional probe-fed patch antenna with a thin air substrate     

Driving-point impedance of a linear cylindrical antenna

A new approach is presented for evaluation of driving-point impedance, requiring only one component of the dyadic Green's function through replacement of the equivalent surface magnetic current at the aperture by an equivalent volume polarisation current. The analysis is applied to a cylindrical antenna at a general position between parallel plates.     

An experimental and theoretical study on the circuit properties of a cylindrical antenna in a hot lossy plasma

Experimental results on the input impedances and the current distributions of cylindrical antennas of various lengths in a large volume of hot lossy plasma are presented. A relatively simple theory based on an integral equation and a grid antenna model is developed. The theoretical results are in good qualitative agreement with the experiments. The theory is also compared to theories of some other researchers. Because of its simplicity, the present theory may prove useful in practical applications.     

Current distribution on a cylindrical antenna in a plasma

A general solution for the current distribution on a cylinder in a cold magnetoplasma has been obtained. It is complicated, but for practical applications several simplifications occur. We present an outline of this solution and a sample of results.     

On the aperture field of a solid cylindrical antenna

The situation of a solid cylindrical antenna excited by a narrow circumferential gap is considered, and an approximation which is realistic, simple, and very accurate is obtained for the aperture electric field.     

一种超宽带地板开槽单极子天线的设计

研制了一款超宽带印刷单极子天线。通过在接地板和单极子贴片底部开槽,展宽了天线频带,改善了天线带内特性,提高了天线增益。采用HFSS软件进行仿真,对天线模型参数进行优化,达到最佳设计效果。结果表明,改进后的天线-10 dB阻抗带宽为2.2~14.6 GHz,比原不开槽天线的-10 dB阻抗带宽增加了7.2 GHz。天线实现了小型化超宽带的同时,在整个超宽带匹配频段内,具有良好的驻波和方向图特性,在超宽带设备中有着很好的应用前景。     

Surface fields and near fields of a linear antenna

In a variational impedance formulation, antenna trial functions are modified to satisfy the edge conditions of diffraction theory. For a half-wave antenna, this provides a charge distribution with experimentally verified linear portions. The linearity of the charge distribution appears to be correlated with near-field fluctuations of the antenna.     

Near fields of a linear antenna

The near fields of a strip antenna in free space have been computed by modifying a variational-impedance formulation. Current distributions, which vary linearly with distance near the ends of the antenna, excite strong tangential electric fields on the antenna surface. Such surface fields are avoided by choosing the axial antenna current to vary in proportion to the square root of the distance from the antenna ends. This modification of the antenna current is not necessary, however, for field calculations at distances comparable to the antenna width. The fields parallel to the antenna surface decrease with increasing distance from the antenna near the driving point and the antenna ends, but are found to increase in an intermediate range.     

Diffraction of plane and cylindrical waves by a cylindrical metamaterial shell with a negative refractive index

The problems of scattering of plane and cylindrical waves by a cylindrical metamaterial shell are solved rigorously. The influence of the geometric dimension of the shell, the value of the negative refractive index of the metamaterial medium, and the location of the cylindrical wave source on the near (far) field structure is investigated. It is shown that, in the quasi-opticl region, a caustic with one cusp is formed inside an electrically thick shell and whispering-gallery waves or standing waves are formed in between the facets of an electrically thin shell. It is found that, in the resonance region, reactive (surface) fields with substantial amplitudes are observed near the boundaries of a thin shell.     

The RCS of a cylindrical array antenna coated with a dielectric layer

The scattering properties of dielectric coated waveguide aperture antennas mounted on circular cylinders are investigated. Both the single element antenna and the array case are treated. The array antenna consists of 4 /spl times/ 32 rectangular apertures placed in a rectangular grid on the surface of an infinitely long circular cylinder. The problem is formulated in terms of an integral equation for the aperture fields which is solved with the method of moments using rectangular waveguide modes as basis and test functions. An efficient uniform asymptotic technique is used to calculate the excitation vector and the backscattered far-field. The asymptotic solution is valid for large cylinders coated with thin dielectric layers away from the paraxial (i.e. near axial) region. A similar asymptotic solution is used to calculate the mutual coupling in the nonparaxial region. For the self coupling terms and for the mutual coupling in the paraxial region a planar approximation is used with a corresponding spectral domain technique. Numerical results are presented as a function of frequency, angle of incidence, cylinder radius, and electrical thickness of the coating.     

A shaped dual-reflector antenna with a tilting flat subreflectorfor scanning applications

A scanning dual-offset reflector antenna using the simple motion of a flat subreflector to illuminate different parts of a shaped main reflector is presented. A particular case having a 20-degree linear field-of-view (for a DBS application) with a 30λ aperture diameter is explored. The main reflector surface is shaped to minimize the phase aberrations across the field-of-view. Once the main reflector surface is designed, the subreflector parameters are determined to ensure optimum focusing across the field-of-view     

Radiation characteristics of a cavity-backed cylindrical gap antenna

The input impedance and the equatorial radiation patterns of a VHF cavity-backed cylindrical gap antenna are derived and compared with experiments. The experiments generally support the computations, provided that the gap dimension is neither larger than about 1/100 of a wavelength, nor so thin that mechanical tolerances in the feed design become important. The results show that the tuning, impedance bandwidth, and the radiation patterns of this antenna can be controlled very accurately by adjusting the internal radius and height of the cavity. Salient points of this antenna are its wide-band characteristics (10-percent bandwidth), its pattern circularity, and particularly the fact that it can be made an integral part of a space vehicle.