New exponential TEM horn antenna with binomial impedance taper

In this paper a new ultra wide band exponential transverse electro-magnetic (TEM) horn antenna with binomial impedance taper is presented. The binomial distribution is used for the impedance taper along the length of the proposed antenna. Using binomial distribution for the impedance taper causes the antenna to have minimum VSWR and flat gain in a wide frequency band. The proposed antenna was manufactured and its performance was compared with the antennas of the same size with exponential, Klopfenstein and triangular impedance tapers. Measurements show that the antenna has VSWR less than 2 in the frequency band from 3 to 15 GHz and less than 2.5 from 2 to 16.3 GHz. Having very good directional pattern and flat gain in a wide frequency band are significant characteristics of this new proposed antenna.     

Scanning and impedance properties of TEM horn arrays for transientradiation

A general concept for ultrawide-band array design using interconnected transverse electromagnetic (TEM) horns is described. At high frequencies (wavelength small compared to unit cell dimensions), the mutual coupling between elements is small and, consequently, the input impedance depends only on the lattice dimensions and not on either scan angle or frequency. At low frequencies (wavelength large compared to unit cell dimensions), the mutual coupling is purposefully made large, by interconnecting the elements to maximize the low-frequency performance. This paper presents the results of analyses using a periodic hybrid finite-element approach to calculate input impedance and scanning performance of generic TEM horn arrays. The limiting case, the planar bicone, is shown to have the frequency-independent property of a self-complementary antenna, making it a useful case for establishing the effects of feed region geometry. Although it radiates bidirectionally, it has the interesting property that its broadside-scan frequency response in the array environment is absolutely flat up to the grating lobe onset limit. A TEM horn array is more unidirectional, but as a consequence suffers both oscillatory variations in the input impedance with frequency and increased limits on minimum achievable rise time     

变阻抗TEM喇叭天线设计中末端端口阻抗问题的研究

恒阻抗TEM喇叭天线的上、下板之间的间距、板的宽度沿天线轴向呈线性渐变,且喇叭天线的驱动端口、末端端口的宽高比相同。与恒阻抗TEM喇叭天线不同,指数渐变型TEM喇叭天线上下极板之间的间距沿轴向呈指数渐变。研究发现,当指数渐变型TEM喇叭的极板宽度采用不同的渐变形式时,极板宽度线性变化型TEM喇叭天线的驻波比最佳,主射方向远场脉冲峰峰值最大。当天线轴向长度、末端端口高度一定时,天线主射方向远场脉冲峰峰值随着天线末端端口宽度的增大而增大;当末端端口宽度达到一定值时,脉冲峰峰值达到最大值,继续增大末端端口宽度,脉冲峰峰值减小;当天线主射方向远场脉冲峰峰值达到最大值时,天线末端端口阻抗值为215Ω。     

Dispersion characteristics of ring line through the conformal mapping approach

Dispersion characteristics of EH/sub 11/ and EH/sub 21/ modes in open ring lines are theoretically calculated using conformal mapping applied to a three dimensional problem. The validity of the solution is tested by comparison with experimental data.<>     

TEM传输室多层介质支撑特性阻抗的数值分析

采用边界元法分析了芯板支撑对TEM传输室特性阻抗的影响.介绍了建模方法,以及边界元法计算多介质区域特性阻抗的基本思想.计算结果表明:芯板支撑对特性阻抗的影响比较显著,随材料介电常数的不同,影响值一般为2～5Ω左右.测量结果与计算结果基本吻合.提出的数值计算方法有助于TEM传输室的设计.     

TEM喇叭天线设计与实验

设计了一种带有机玻璃天线罩的地平板结构横电磁波(TEM)喇叭接收天线,通过对馈入结构和辐射特性的理论分析初步确定关键结构尺寸,然后利用CST建立天线真实模型,完成相关结构参数的仿真优化,实现了快脉冲的较小馈入反射,时频特性良好。最后的天线测试结果表明,该TEM喇叭天线输入阻抗56 Ω,有效高度0.024 m,传递函数在3 GHz以内保持稳定,具备较好的时域保真度和馈入反射特性,适于作为超宽带接收天线。     

Accurate estimation of characteristic impedance of coaxial transmission-line problems by the eigenfunction approach

Accurate numerical results are presented for regular polygonal coaxial transmission lines with inner central circular conductor using an eigenfunction approach and a successive integration method of boundary condition satisfaction. Just two-term solutions are found to yield high accuracy. The results for equilateral triangular section are found to be superior to those reported in literature.     

复杂截面同轴线特性阻抗、截止波长的计算

应用静电场的观点和导波传输理论,用有限元法（FEM）分别计算了各种复杂截面同轴线特性阻抗、截止波长。计算结果表明,该方法计算精度高,通用性强,简便易行,可以用于传输线工程问题的设计和计算。     

A design study for the basic TEM horn antenna

In this paper, a design study was performed for the basic TEM horn antenna. In the theoretical model, care was taken to avoid the problems associated with the use of gap sources when calculating the reflection coefficient and input impedance of the antenna. All numerical calculations were made with a program based on the method of moments, and the accuracy of the numerical calculations was established with measured results for selected antennas. The transverse electromagnetic (TEM) horn antenna is a popular broadband antenna. The basic antenna has a simple design consisting of two triangular plates and a feeding structure. The horn is described completely by only three variables: /spl alpha/, /spl beta/, and s. /spl alpha/ is the angular width of each plate, /spl beta/ is the angular separation between the two plates, and s is the length, measured from the drive point to the corner of the plate. The geometry of the basic TEM horn antenna does not require a particular choice of a feeding method.     

UWB TEM HORN ANTENNA FOR THE ASPHALT PAVEMENT INVESTIGATION简

A simple Ultra-WideBand （UWB） exponentially-tapered Transverse ElectroMagnetic （TEM） horn antenna is presented for the asphalt detection based on Ground Penetrating Radar （GPR） In order to reduce the reflections from the antenna aperture, some absorbing material is loaded on the outer surface of the conductor. Comparing with the traditional TEM horn antenna, the proposed antenna has a small size and a large impedance bandwidth. Simulated and measured results show that the proposed TEM horn antenna has a low Voltage Standing Wave Ratio （VSWR） below 2 over the whole band from 0.35 GHz to 12 GHz, good radiation characteristics, and small late-time ringing, which can perfectly meet the requirements of the GPR application.     

Accurate analysis of TEM horn antennas for pulse radiation

In the past, various approximate theoretical models have been used to analyze TEM horn antennas. Because of the limitations of these approximate models, there has been, to date, only qualitative agreement of measurements for TEM horn antennas with the predictions of the theories. The finite-difference time-domain (FDTD) method is used to accurately analyze TEM horn antennas for pulse radiation. First, the metallic triangular-plate TEM horn antenna is considered. Computed results for the reflected voltage in the feeding transmission line and the time-varying radiated electric field are shown to be in very good agreement with new experimental measurements. Graphs of the electric field in the space surrounding the antenna (magnitude of field plotted on a color scale) are used to give a physical insight into the process of radiation. Next, the method is used to analyze two TEM horns that were previously designed for pulse radiation. The geometry and electrical properties of these antennas are more complicated than for the metallic, triangular-plate horn. One has shaped metallic plates with a resistive termination at the open end; the other has plates whose resistance varies continuously along their length. The computed results for these antennas are compared with previously made experimental measurements     

Characteristic impedance of a rectangular double-ridged TEM line

The characteristic impedance of a TEM transmission line, shaped as a double-ridged rectangular coaxial line, is analyzed in this paper as the customary transversal static problem. This type of transmission line is useful, for example, as a part of a cascaded transition between a double-ridged waveguide and a coaxial line. The solution of the transversal problem is achieved by dividing the cross-sectional region into distinct, separable regions, each one being characterized by closed-form Green's functions relating the flux function to the electric field. Surface-type integral equations are then formulated over the boundaries between the regions. Solution of these equations via the method of moments (MoM's) using the Galerkin choice yields the results for the characteristic impedance as a function of cross-sectional dimensions. Convergence of the solution is also studied     

Two-dimensional mapping of impedance magnetocardiograms

A new method for measuring two-dimensional (2-D) impedance magnetocardiograms (I-MCGs) and magnetocardiograms (MCGs) above the heart simultaneously, has been developed. The I-MCG's and MCG's signals are recorded by using a superconducting interference device (SQUID) system. To measure the I-MCG and MCG signals, four first-order gradiometers with an 18-mm diameter and a 50-mm baseline were used. The SQUIDs are driven by a flux-locked-loop circuit with a frequency range higher than that of an ac-current (40 kHz) with constant amplitude passed through a subject. The output of the circuit is filtered through two circuits: one for measuring the I-MCG signals and one for measuring the MCG signals. The I-MCG signals are obtained by demodulating the magnetic field, which is detected by the gradiometers, at the frequency of the ac current. As a result, the I-MCG signal reflects the change in spatial distribution of conductivity caused by the movement of the heart muscle and blood volume. A contour map of the 2-D I-MCG signals showed the largest signals occur above the right ventricle and right atrium. In a corresponding current-arrow map, it was found that the large current arrows occurred above the right side of the right ventricle. Furthermore, it was found that the systole and diastole timings obtained from the first-derivative I-MCG signal and the phonocardiogram were different. These results show that primitive 2-D I-MCG signal can provide much physiological information on the circulatory movement of the heart.     

The calculation of the characteristic impedance of microstrip

Results from calculations of Z _c of microstrip from a formula proposed by Kumar et al. are discussed and compared with other theoretical and practical results.     

Calculation of characteristic impedance of planar structures using coupling and decoupling of hybrid modes in the spectral domain

A new techniue based on the spectral domain method for calculating the characteristic impedance of planar dispersive structures with multilayer dielectric substrates is presented. The coupling and decoupling of LSE and LSM modes are introduced so that the calculation of whole power in the considered structure bcomes very easy and fast. Numerical results are presented for some complex structures.     

Accurate radiation and impedance characteristics of horn antennas-amoment-method model

A moment-method-model for horn analysis is presented. The generalized reflection matrix of the aperture is determined using the spectral Galerkin method. The reflection matrix is then combined with the generalized scattering matrix of the horn to yield the input return loss and the aperture fields of the horn. It is shown that the model can predict the radiation characteristics more accurately than the models commonly used in practice     

指数渐变TEM喇叭辐射脉冲波形畸变分析

指数渐变TEM喇叭沿主轴方向长度一定时,主射方向上辐射脉冲峰峰值随口径高度递增,当辐射脉冲峰峰值到达最大值后,辐射脉冲峰峰值随着口径高度递减,并且辐射脉冲波形发生畸变。为了分析响应波形畸变原因,基于等效开路传输线模型给出指数渐变TEM喇叭脉冲响应的近似表达式,并且结合指数渐变TEM喇叭内部的电磁能量流动过程修正辐射脉冲表达式。理论分析表明,指数渐变TEM喇叭辐射脉冲由两个分量叠加而成,并且这分量之间存在的相对时延与高度渐变线的相对变化率正相关,过大的相对时延会使辐射脉冲的波形发生畸变,从而导致辐射脉冲峰峰值小于同尺寸线性渐变TEM喇叭的辐射脉冲峰峰值。利用电磁仿真软件得到相同尺寸的指数渐变TEM喇叭与线性渐变TEM喇叭的辐射脉冲波形,通过二者之间的对比验证理论分析的正确性。     

Measurements of the characteristic impedance of coaxial air linestandards

A method for electrically measuring the characteristic impedance of coaxial air line standards is described. This method, called the gamma method, determines the characteristic impedance of a coaxial air line from measurements of its propagation constant and capacitance per unit length. The propagation constant is measured on a network analyzer, and the capacitance per unit length is measured on a capacitance bridge at 1 kHz. The measurements of characteristic impedance with the gamma method are independent of any dimensional measurements. Measurements of the characteristic impedance using the gamma method are compared to theoretical predictions from dimensional measurements. Test results are shown for 14 mm, 7 mm, and 3.5 mm coaxial air lines     

Elemental mapping of DNA chains by energy-filtering TEM

DNA chains were detected by phosphorus mapping based on energy-filtering transmission electron microscopy (EF-TEM). The three-window method and the image-merging system were used to make phosphorus-mapping images. It was impossible to observe DNA chains without the image-merging system, because of the low signal levels of single images. It became easy to assign DNA molecules when the typical superstructure of plasmids was preserved. To preserve the structure during specimen preparation, rapid-freezing and freeze-drying methods were used. Mapping images can be obtained only when carbon-supporting films are extremely thin, as thick supporting films weaken the signals. The thickness of the supporting film, which was estimated to be < 2 nm, was the most important factor in this study. In the three-window method, the calculation to remove the background absolutely includes a few errors, because the precise spectrum was not observed. To obtain higher quality mapping images, several improvements in the hardware are suggested.