Extremely low-profile helix radiating a circularly polarized wave

It is shown that the combination of low pitch and a small number of turns realizes a low-profile helix as a radiating element of circular polarization. A two-turn helix of 4° pitch angle shows a bandwidth of 12% for a 3 dB axial-ratio criterion. The numerical results presented lead to new aspects of a low-pitch helix as an effective radiating element     

不均匀磁等离子体的隐身机理——圆极化电磁波的碰撞吸收

研究了圆极化电磁波在不均匀磁等离子体的传播和吸收。讨论了不均匀磁化等离子体片对平行于磁场方向传播的左、右旋圆极化电磁波的碰撞吸收,计算了不同条件下衰减率。计算表明,当电磁波的频率接近电子碰撞频率时,磁等离子体对电磁波的吸收达到最大值。当入射电磁波的频率很低时,不均匀磁化等离子体中磁撞对雷达波的吸收非常小。当入射电磁波频率较高时,等离子体的碰撞对入射电磁波的衰减很有效。     

Diffraction by an infinite dielectric cylinder due to a normally incident cylindrical wave

The asymptotic value of the electric field diffracted by an infinitely long dielectric cylinder due to a normally incident cylindrical wave is computed by the geometrical theory of diffraction and shows excellent agreement with previous experimental results as well as the exact solution.     

Diffraction of an H-polarized electromagnetic wave by a circular cylinder with an infinite axial slot

A comparison of three methods of solution for the problem of scattering and diffraction of a transverse electric (TE) polarized plane wave by an infinite circular cylinder having an infinite axial slot is presented. In one method of solution, the aperture field integral equation (AFIE) method, the fields in and around the cylinder are found from the apertureE-field and the Green's functions for the interior and exterior of a cylinder. In the other two methods, the fields are determined from the surface current, which is obtained by solution of theH-field integral equation (HFIE) or theE-field integral equation (EFIE). The field in the aperture of the cylinder is found from the three methods, and the advantages and disadvantages of each method of solution are discussed. In addition, it is also shown that for shell thickness less than 1/20 of a wavelength, the aperture fields do not differ signifcantly from those of an infinitely thin shell cylinder.     

A crank-line array antenna radiating a circularly polarized wave

An array antenna composed of crank-line elements is investigated on the basis of the element current distributions determined by the method of moments. A technique of gradually increasing the antenna height above the ground plane is adopted to enhance the gain. It is found both numerically and experimentally that a gain of approximately 30 dB is obtained with an axial ratio of less than 3 dB over a frequency bandwidth of 2.5%     

Equally spaced monopole-notch array antenna for circularly polarized wave

Experimental results of a circularly polarized antenna composed of two pairs of monopole-notch arrays arranged orthogonally on a conical conducting plate are described. This antenna can be designed by a simple design procedure, and it provides excellent performance characteristics as a broad-band circularly polarized antenna.     

Axial ratio of an antenna illuminated by an imperfectly circularly polarized source

A method for determining the axial ratio of an antenna illuminated by an imperfectly circularly polarized source is described. This method requires measurements of the right- and left-handed amplitude components and their relative phases for both the receiving and transmitting (or source) antennas. From these measured data and, of course, the theory of power transfer between the source and receiving antennas, an algorithm is derived for the actual axial ratio of the receiving antenna. Illustrative results showing the effects of the phase angle are presented.     

Scattering by an infinite circular dielectric cylinder coating eccentrically an elliptic dielectric cylinder

Scattering of a plane electromagnetic wave by an infinite circular dielectric cylinder coating eccentrically an elliptic dielectric one, is under consideration. Both E and H polarizations are treated for normal incidence. The electromagnetic field is expressed in terms of both circular and elliptical-cylindrical wave functions. Using proper transformation theorems between the field expressions in different coordinate systems, for the satisfaction of the boundary conditions, we obtain two infinite sets of linear nonhomogeneous equations for the expansion coefficients of the field. In case of small values of h=k/sub 2/c/2, where c is the interfocal distance of the elliptic cylinder and k/sub 2/ the wavenumber of the dielectric coating, the former sets of equations provide, by truncation, semianalytical expressions of the form S(h)=S(0)[1+gh/sup 2/+O(h/sup 4/)] for the scattered field and the various scattering cross sections. The coefficients g are independent of h. Graphical results for the scattering cross sections are given for various values of the parameters.     

Broadband circularly polarized CPW-fed slot antenna array for millimeter wave application

A broadband and circularly polarized 1×4 linear antenna array composed of CPW-fed slot elements for millimeter wave application is discussed. Through a special short-circuiting stub perturbation method, the circular ring slot element achieves circular polarization and a broad bandwidth. Through a parallel feeding network, the array achieves a broad impedance bandwidth of 19% with VSWR?2 and CP bandwidth of 18.4% with AR?3 dB and has a peak gain of about 6.8 dB.     

Operation of a circularly polarized ring laser

Although there has been a large amount of experimental work published on the operation of the ring laser, nearly all of it was concerned with lasers operating in linearly polarized modes. In this paper the operation of a ring laser using the 1.153-μm wavelength transition of the He-Ne mixture in a cavity with no polarization constraint is reported. It was found that the two traveling waves operated in the same sense as circularly polarized modes and that there was no measurable coupling between the traveling waves via the amplifying medium, although there was still locking induced by coupling through cavity imperfections.     

A circularly polarized short backfire antenna excited by an unbalance-fed cross aperture

An unbalance-fed cross aperture is developed to excite a short backfire antenna (SBA) for circular polarization. The cross aperture consists of two orthogonal H-shaped slots with a pair of capacitive stubs and is fed by a single probe that forms an unbalanced feed with a shorting pin. It is demonstrated that the cross-aperture-excited SBA can achieve an axial ratio (/spl les/ 3 dB) bandwidth of 4.2% with a voltage standing wave ratio (VSWR) bandwidth of 6.5% (VSWR<1.2) and a gain of 14 dBi. The antenna structure is described and the simulation and experimental results are presented. The mechanisms for impedance matching and circular-polarization production are analyzed.     

Scattering by an infinite circular dielectric cylinder coatingeccentrically an elliptic metallic one

The scattering of a plane electromagnetic wave by an infinite-circular dielectric cylinder, containing eccentrically an elliptic metallic one is considered. The electromagnetic field is expressed in terms of both circular and elliptical-cylindrical wave functions, connected with one another by well-known expansion formulas. Translational addition theorems for circular cylindrical wave functions are also used for the satisfaction of the boundary conditions in the dielectric cylinder. When the solution is specialized to small values of h=k₁c/2, with k₁ the wavenumber of the dielectric cylinder and c the interfocal distance of the elliptic conductor, semianalytical expressions of the form S(h)=S(0)[1+gh²+O(h ⁴)] are obtained for the scattered field and the various scattering cross sections of this configuration. Both polarizations are considered for normal incidence. Numerical results are given for various values of the parameters     

Transient currents on a cylinder illuminated by an impulsive plane wave

An analytical and numerical study of the transient current density induced on a perfectly conducting circular cylinder has been carried out. Both TE and TM incident plane waves with impulsive time dependence are considered. Complete closed form expressions for the TE and TM current density at all points on the cylinder and for all time values are obtained by a functional interpolation of both large and small time asymptotic solutions. The complete expressions should he useful in future transient radar scattering problems for approximating the transient current behavior on portions of a complex scatterer. The numerical results are presented in the form of "snapshots" of the current density at specific instants of time. The results are interpreted in terms of specular reflection and creeping waves. The creeping wave pulses are seen to be a continuation of pulses generated on the illuminated surface; their propagation into the shadow region is a highly dispersive phenomenon. The natural mode spectrum is seen to have both discrete and continuous components with the response at very large times determined by the latter.     

基于X波段的高功率圆极化反射阵列天线全波分析研究

传统圆极化反射阵列天线分析方法对天线辐射特性等方面分析的不足,导致在天线全波分析时精度较低,为此,提出了基于X波段的高功率圆极化反射阵列天线全波分析方法.首先研究圆极化反射阵列天线的工作原理,采集相关参数,然后根据参数进行反射阵列天线相位分布、辐射特性、口径效率和单元间距四个方面进行分析.通过仿真实验测试设计阵列天线的...     

Gain improvement of circularly polarized array antenna usinglinearly polarized elements

A novel gain improvement method for a circularly polarized array antenna consisting of linearly polarized elements is proposed. It is verified that the gain of a circularly polarized array antenna can be increased by adjusting the array arrangement of the individual linearly polarized elements. The gain of a multiring array antenna consisting of the above mentioned circular array can also be increased by properly combining the directions of the linear polarization of the individual circular arrays. The gain improvement of the single-circular array antenna and the two-ring array antenna using the proposed method are verified by the measured results     

Single-feed circularly polarized equilateral-triangular microstripantenna with a tuning stub

Novel circular polarization (CP) designs of single-feed equilateral-triangular microstrip antennas are proposed and experimentally studied. The proposed CP designs can easily be achieved by loading a narrow tuning stub at the triangle tip or at the center of the bottom edge of the triangular patch. Moreover, by embedding a cross-slot of equal slot lengths in the triangular patch, a compact CP operation can easily be obtained, with an antenna size reduction up to about 22%, as compared to the CP design of a regular triangular microstrip antenna without cross-slot at a fixed frequency     

A circularly polarized small-size microstrip antenna with a crossslot

An antenna with a low profile, small size, and a light weight is required in mobile satellite communications. A new, circularly polarized small-size microstrip antenna using a proximity coupled feed method is proposed. A simple configuration based on a cross slot with unequal slot lengths on a circular patch is adopted to realize a small-size element antenna. The proposed antenna has no 90° hybrid coupler for circular polarization. The measured results verify the circular polarization, and the antenna radius was reduced by about 36% by using the slot lengths which are nearly equal to the diameter of the circular patch antenna. Good impedance and axial ratio characteristics have been obtained     

Scattering by an infinite cylinder coated with an inhomogeneous and anisotropic plasma sheath

The problem of the interaction of an incidentHwave with an infinite conducting cylinder coated with an inhomogeneous and anisotropic plasma sheath is treated analytically. Numerical results for the farfield pattern of the scattered field as well as the backscattering cross sections are presented for various interesting ranges of the parameters involved. Detailed discussion of the effects of the impressed static magnetic field, the sheath thickness, and the density and profile of the plasma sheath on the scattered wave is also presented. A parabolic electron density profile is assumed.     

Radiation of circularly polarized microwaves by a plane periodic structure of Ω elements

Transformation of the electromagnetic-wave polarization by a 2D grating of metal Ω elements is studied theoretically and experimentally. The electric dipole moment and magnetic moment excited by a linearly polarized incident wave in a single Ω element are determined. The parameters of an Ω element that are optimal for radiation of a circularly polarized wave are calculated. A 2D grating consisting of Ω elements with optimal parameters is fabricated, and the obtained theoretical results are verified experimentally.     

Planar circularly polarized microstrip antenna with a single feed

A novel circularly polarized (CP) microstrip antenna is introduced. The antenna is fed with a single coaxial probe and the structure is planar. The CP bandwidth is much larger than available single-probe microstrip antennas and the CP radiation quality is excellent over the entire upper hemisphere