An experimental study of electronic scanning by an antenna loaded with a circular array of ferrite rods

The measured performances of the antenna which consists of a circular array of 12 anisotropic ferrite rods, a truncated biconical horn, and a core wire of a coaxial cable at the center of the biconical horn are presented. The following are made clear. The transmitting pattern having a single big lobe and suppressed sidelobes is obtained by the effects of the appropriate ferrite anisotropy and of the interactions among the ferrite rods. The main lobe cannot be rotated continuously, but at intervals of about30degby gradually changing the axial magnetic fields applied to the respective ferrites; that agrees with what was expected by the two-dimensional theory. Reciprocity does not hold for this antenna: the receiving pattern coincides with the transmitting pattern rotated180deg. Hence, this antenna permits us to receive from a direction and simultaneously to transmit in a different direction. The frequency characteristics of the antenna including the input impedance are also shown and discussed.     

Feeding position dependent effects of Ag thick film EMC patch antenna due to Mn substituted Mg ferrite loading

The characteristics of Ag thick film electromagnetically coupled patch antenna due to Mn substituted Mg ferrite loading is reported. The effect of thickness of ferrite and feed position is also studied. Ferrite loading in the absence of external dc magnetic field provides additional resonance frequencies of the same antenna. The intrinsic magnetisation of the ferrite also seems to be contributing to the observed effects. The off resonance radiated output increases due to the ferrite overlay. The non-symmetries in the E plane pattern are enhanced due to the ferrite loading.     

Electromagnetic scattering by many gyrotropic cylinders of different kinds

Simultaneous matrix equations are first given for solving the problems of scattering by many homogeneous gyrotropic cylinders of different kinds. The numerical results are illustrated for two circular ferrite cylinders, elliptic and circular ferrite cylinders, two parallel linear arrays of circular ferrite cylinders, and a circular array of twelve circular plasma cylinders around a magnetic current source. It is indicated that a sharp main lobe of the linear arrays illuminated by anE-plane wave can be veered by a reversal of the applied static magnetic field, and that with a cyclic change of the dc magnetic fields applied to the circular array one can rotate the radiation pattern having a single big lobe with suppressed side lobes. Some discussions for electronic lobe switching and electronic scanning by gyrotropic cylinders are given. The effects of interactions among the cylinders are also discussed.     

Electronic lobe switching by 90° corner reflector antenna with ferrite cylinders

Simultaneous matrix equations are obtained for solving the problem of scattering by many different homogeneous ferrite cylinders located in front of a90degcorner reflector. The equations are based on the extended integral equations derived from the reciprocity theorem in the cylinders and on the method of images. After the problem of plane-wave scattering is treated, various radiation patterns for the corner reflector antenna with some circular ferrite cylinders are exhibited. From the latter numerical results the possibilities of one-lobe or two-lobe switching and lobe extinction by varying the dc magnetic fields applied to the cylinders become clear.     

一种介质埋藏异形微带八木天线的设计

为达到某重点项目性能要求,综合运用微带天线、八木天线和介质埋藏天线理论及设计方法,设计出了一种介质埋藏异形微带八木天线.该天线将传统八木天线的引向振子由一个改变为两个,形成“￥”形,用来规划波束方向和形成双波束;在天线贴片两旁增加“栅栏”,聚集了电磁波的辐射,提高了天线增益,同时还获得了较大的相对阻抗带宽.测试表明:在...     

Plane Waves Propagating in Chiral Plasma and Chiral Ferrite Media

Plane wave propagation in chiral plasma and chiral ferrite media is studied in kDB coordinate system. General wave equations and characteristic equations of plane waves propagating along an arbitrary direction in chiral plasma and in chiral ferrites are derived in simple formulations respectively. Four wavenumbers and their corresponding dispersion characteristics are resulted for propagation both along and normal to the biasing magnetic field. When plane wave with negative helicity propagates along the biasing magnetic field in chiral ferrites, backward waves emerge. However backward waves occur with both positive and negative helicities when propagating along the biasing magnetic field in chiral plasma.     

AI-SI法分析X波段机载雷达天线罩

采用口径积分-表面积分(AI-SI)算法,对带罩机载阵列天线进行了分析。雷达罩的介质反射是引起天线方向图副瓣抬升的主要原因,在传统的AI-SI法分析天线罩过程中没有考虑天线金属阵面对天线罩介质反射的影响,因此,带来较大的计算误差。为了避免上述问题,文中在分析带罩天线过程中,采用了理想源阵列加反射板模型。天线罩总的透射场为阵列天线的一次透射场与反射板产生的二次透射场的叠加。为验证算法的正确性,将AI-SI算法计算结果与CST软件仿真结果进行了比较,两者吻合较好。     

Far-field performance of linear antennas determined from near-fielddata

The main plane far-field radiation pattern of an antenna under test from the corresponding main plane near-field data, using a circular-line acquisition, is presented. The method is based on the reconstruction of equivalent magnetic currents (EMCs) using decoupled integral equations and one-dimensional source components. The resultant fast procedure is applicable to linear and quasilinear array antennas. Experimental data results and comparison with complete spherical acquisition and center-line acquisition are presented     

Small Low-Profile Loop Wideband Antennas With Unidirectional Radiation Characteristics

Small low-profile wideband loop antennas featuring unidirectional radiation characteristics are presented. Directive radiation characteristic is achieved by proper combination of fields radiated by symmetric and anti-symmetric current components supported by any loop antenna. Relative strengths of the symmetric and the anti-symmetric radiations change according to shape of the loop. Prototype loop antennas are fabricated and their impedance and radiation gain patterns are measured. The gain patterns show directive characteristics in both major planes. It is shown that the gain measured in the desired direction of maximum radiation exceeds the maximum achievable practical gain for omnidirectional antennas of the same dimensions over wide frequency band     

Ultrawideband Hybrid EBG/Ferrite Ground Plane for Low-Profile Array Antennas

The design and analysis of an ultrawideband and low-profile hybrid electromagnetic band-gap (EBG)/ferrite ground plane is presented for implementation with antenna systems in airborne foliage penetrating radar and EW applications. The hybrid EBG/ferrite ground plane consists of an EBG structure with a ferrite slab placed on top of the structure's perfect electric conductor (PEC) ground plane. Reflectivity and phase analyses show that the hybrid EBG/ferrite ground plane offers ultrawideband operation beginning in the 100s of MHz with one design version offering an operational bandwidth exceeding 22:1 starting at 170 MHz. Additionally, analysis of the hybrid ground plane implemented with dipole antennas verifies that the hybrid ground plane effectively produces uni-directional radiation for bi-directional radiating antennas. The designed hybrid ground plane is also simulated with Raytheon's long slot array antenna and the obtained results further verify its ultrawideband performance     

Conformal double exponentially tapered slot antenna (DETSA) on LCP for UWB applications

We discuss the use of a double exponentially tapered slot antenna (DETSA) fabricated on flexible liquid crystal polymer (LCP) as a candidate for ultrawideband (UWB) communications systems. The features of the antenna and the effect of the antenna on a transmitted pulse are investigated. Return loss and E and H plane radiation pattern measurements are presented in several frequencies covering the whole ultra wide band. The return loss remains below -10 dB and the shape of the radiation pattern remains fairly constant in the whole UWB range (3.1 to 10.6 GHz). The main lobe characteristic of the radiation pattern remains stable even when the antenna is significantly conformed. The major effect of the conformation is an increase in the cross polarization component amplitude. The system: transmitter DETSA-channel receiver DETSA is measured in frequency domain and shows that the antenna adds very little distortion on a transmitted pulse. The distortion remains small even when both transmitter and receiver antennas are folded, although it increases slightly.     

Performance and design procedure of dual parabolic cylindricalantennas

The radiation characteristics of dual parabolic cylindrical antennas are studied, and the dependence of the principal plane beamwidths and the peak cross-polarization on their geometrical parameters is determined. The antenna aperture is rectangular in shape and generates an elliptical beam pattern, with a beamwidth ratio that can be controlled by the main and subreflector focal lengths. The far-field patterns are determined by an extended aperture integration method that includes the contributions of the reflected and the main diffracted rays. It is found that the cross-polarization depends of the offset angle between the axis and the direction of the normal to the subreflector surface and can be minimized by optimizing the relative angle between the reflectors. Other pattern characteristics are controlled by the antenna geometrical parameters and the feed illumination. A procedure for the design of these antennas and the expressions for determining the reflector geometries are provided     

Radiation and scattering characteristics of microstrip antennas onnormally biased ferrite substrates

Radiation and scattering characteristics of microstrip antennas and arrays printed on ferrite substrates with a normal magnetic bias field are described. The extra degree of freedom offered by the biased ferrite can be used to obtain a number of novel characteristics, including switchable and tunable circularly polarized radiation from a microstrip antenna having a single feed point, dynamic wide-angle impedance matching for phased arrays of microstrip antennas, and a switchable radar cross section reduction technique for microstrip antennas. Results are obtained from full-wave moment method solutions for single microstrip antennas and infinite arrays of microstrip antennas. A cavity model solution for a circular patch antenna on a biased ferrite substrate is also presented, to aid in understanding the operation of these antennas     

Characteristics of aperture coupled microstrip antennas on magnetized ferrite substrates

The method of moments in the spectral domain is applied to the full-wave analysis of aperture coupled microstrip antennas in the case where the substrate of the antennas is a layered medium containing magnetized ferrites. The subsectional basis functions used in the analysis make it possible to handle patch antennas and coupling apertures with right angle corners of arbitrary shape. The numerical results obtained show that antennas on ferrite substrates fed by single microstrip lines can radiate both circular and linear polarization, the polarization state being dependent on the orientation of the ferrites bias magnetic field. For a given polarization state, the matching frequency band of the antennas can be tuned over a wide frequency range by adjusting the magnitude of the bias magnetic field. Also, the polarization state can be continuously tuned from circular to linear within the same frequency band by adjusting both the magnitude and the orientation of the bias magnetic field. Some measurements are presented in order to check the validity of the numerical algorithm developed.     

Control of the SAR Pattern Within an Interstitial Microwave Array through Variation of Antenna Driving Phase

The interstitial microwave antenna-array hyperthermia (IMAAH) system produces a pattern of specific absorption rate (SAR) that is nonuniform within a 2-cm square array driven in phase at 915 MHz. Theory and experiment show that the point of phase coherence (maximum SAR) can be shifted to a point where the SAR is small by changing the antenna driving phases. Rapid shifting makes the time-average SAR more uniform in the direction perpendicular to the antennas. In 95 percent of the antenna junction plane, the time-average SAR is constant within 10 percent.     

Improving radiation-pattern distortion of a patch antenna having a finite ground plane

This paper presents a very useful and yet simple method of improving the radiation-pattern distortion of a patch antenna having a finite ground plane. The improvement can be achieved by cutting out the edges of the finite ground plane. This produces a phase shift between the induced equivalent magnetic currents on the edges, thereby causing cancellation in the diffracted fields. We numerically and experimentally examined the effects for some typical patch antennas and confirmed that the ripples in the copolar E plane pattern could be eliminated by using this approach.     

Characteristics of switchable ferrite microstrip antennas

Switchable antennas consisting of microstrip elements with an in-plane biased ferrite cover layer are introduced. Their radiation and radar cross section (RCS) properties are examined through a full-wave moment-method analysis. For microstrip antennas with a ferrite cover layer, the presence of a decaying extraordinary wave in the ferrite layer can reduce or prohibit incident fields from reaching the antenna resulting in significant RCS reduction. For antenna radiation, most of the power will be converted into magnetostatic waves and little radiates into the air. Under such circumstances, the antennas are “off,” in the sense that they are effectively absent as radiators or scatterers. The aim of this paper is, through the use of an accurate full-wave analysis, to investigate the properties of the switchable microstrip antennas. Both the cases of strip dipoles and rectangular patches are analyzed. The effects of the cover-layer thickness, bias-field strength, and the existence of both ordinary and extraordinary waves on the switchable antenna properties are discussed     

准太赫兹波段角锥波纹喇叭天线的设计

波纹喇叭天线是20世纪70年代出现的用于微波天线的一种新型器件,它结构紧凑、加工方便、成本较低。不仅如此,它还是一种高效率的馈源,它的方向图具有低旁瓣、轴对称、交叉极化小等一系列优点,因而得到广泛的应用。文中介绍了准太赫兹角锥波纹喇叭天线的基本设计思想。设计了一种工作在140 GHz左右频段的E面波纹角锥喇叭天线。计算机模拟达到了相对于平壁角锥喇叭来说较小波瓣宽度,极低旁瓣电平,E,H面波瓣图趋同的效果。     

An antenna pattern measurement technique for eliminating the fieldsscattered from the edges of a finite ground plane

A novel antenna pattern measurement technique is presented to eliminate the effects of the finite ground plane and anechoic chamber wall reflections which significantly perturb antenna pattern measurements. This technique consists of the measurement of the edge-diffracted fields and their subsequent subtraction from the original pattern. A simple theoretical model is developed to introduce the subtraction technique, and comparisons are made which show the excellent agreement between theoretical (assuming an infinite ground plane) and `corrected' experimental antenna patterns. Experimental results are given for open-ended waveguide, microstrip patch, and monopole antennas mounted on circular and square ground planes of various sizes. Time gating techniques are illustrated as well     

一种低方向性的球形共形全向天线阵列设计

传统的球形共形天线阵列馈电网络复杂,每个天线单元需要单独馈电和控制相位,导致天线阵列效 率较低。文中提出了一种采用口径耦合馈电的单馈球面共形全向天线阵。为球形天线阵列设计了一个1 分30 的馈 电网络且直接集成在了阵列内部。这样可以通过一个端口给所有的天线单元馈电,从而降低了馈电的复杂度,提高 了天线效率。阵列的方向图在x-y 平面上是全向的。x-y 平面的增益变化小于1 dB,x-z 平面的半功率波瓣宽度约为 120°,实现了比传统全向更大的空间覆盖范围。天线的方向图最大增益为1 dBi。