Microstrip disk antennas, Part I: Efficiency of space wave launching

A theoretical study on the problem of surface wave excitation of microstrip disk antennas is presented. The cavity model with magnetic sidewalls and dyadic Green's functions in stratified media is used to obtain the radiated fields in an integral form. Lossless media are assumed such that there is no cross coupling between the powers in the space (P_{SP}) and surface (P_{SU}) waves. The separate contributions of these two powers is examined. With the assumption thatP_{SU}does not contribute to the main radiation patterns of the antenna an efficiency of space wave launching and a corresponding antenna directivity are defined. Values of efficiency and directivity as functions of the dimensions of the antenna and for two values of dielectric constants of the substrate are shown. Agreement of these results with some of the available data is observed. It is worth noting thatP_{SU}may correspond to an appreciable portion of the total radiated power.     

Space wave radiation efficiency of a wraparound antenna and theeffect of surface wave radiation due to the dielectric substratetruncation

A theoretical study of the problem of excitation of surface waves in wraparound microstrip antennas is presented. The surface waves are obtained by using a contour integral in the complex plane. The surface-wave energy loss in the antenna truncation region is partially radiated and interfaces with the space wave. The radiation efficiency and the effect of the dielectric substrate truncation of the antenna radiation pattern are shown as functions of antenna dimensions and for two values of substrate dielectric constants     

Microstrip disk antennas, Part II: The problem of surface wave radiation by dielectric truncation

The far zone fields radiated from a microstrip disk antenna with a truncated dielectric layer were obtained using the cavity model with magnetic side walls, the dyadic Green's functions are stratified media, and the integral representation analysis of the fields in the complex plane. It is shown that the truncation of the dielectric is responsible for the ondulations observed in the radiation patterns of these antennas and that they result from the interference of the space wave fields with those radiated as a consequence of the incidence of the surface wave into the truncation region. It is suggested that this interference problem may be alleviated by truncating the dielectric as far as possible from the antenna elements and by using lower values of dielectric thickness to disk radius ratiosd/a, and of dielectric relative permittivitiesepsilon_{r}.     

Asymptotic Green's function of a surface magnetic current elementon a perfect electric conductor plane covered by a lossy dielectricsubstrate

Published analyses of radiation modeling for slot structures on dielectric substrate are empirical or numerical. This paper proposes exact analytical asymptotic expressions of the far-field Green's functions of a surface magnetic current element on a perfect electric conductor plane covered by a lossy dielectric substrate of finite thickness. From these expressions, the radiation pattern of both the space wave and surface wave far away from an arbitrary shaped-slot antenna structure can be calculated, provided the source distribution across the slot is known. The potentials used in the analysis are defined and their boundary conditions are expressed. The Helmholtz equation is solved in the Laplace domain and the solutions are transformed into the space domain using the inverse Hankel transform and steepest descent method. The influences of the substrate thickness and dielectric constant are analyzed using the calculated expressions. The model is validated by comparison with surface wave and space wave measurements and with numerical results obtained from a commercial electromagnetic simulator     

Probe compensated near-field measurements on a cylinder

A new method is developed for determining the farfield pattern of an antenna from probe compensated near-field measurements over the surface of a right circular cylinder enclosing the antenna. The method is derived by first expanding both the field radiated by the antenna and the field radiated by the measurement probe, when it is used as a transmitter, into cylindrical wave expansions. The Lorentz reciprocity theorem is then used to solve for the field radiated by the antenna from the probe output voltage. It is shown rigorously that the antenna pattern can be determined independently of the characteristics of the measurement probe provided that certain calibration data are known. A method for determining these data from the measured far field radiated by the probe is described. It is shown that the necessary numerical integration can be performed with the fast Fourier transform algorithm. Experimental results are presented to validate the theory and to demonstrate its practicality from a measurement and computational viewpoint.     

Surface wave fields and power in millimeter wave integrated dipole antennas

In this paper simple closed form expressions of surface wave fields for microstrip dipoles on grounded substrates are presented. The surface power, radiated power and radiation efficiency are calculated. It is shown that the radiation efficiency decreases with the increase of substrate electrical thickness. Hence new type antennas are needed to radiate millimeter wave because of the effect of the surface waves in substrate.     

A planar triangular monopole antenna for UWB communication

A planar triangular monopole antenna (PTMA) is presented for high-frequency structure simulator ultra-wideband (UWB) communication. The high-frequency structure simulator three-dimensional electromagnetic solver is employed for design simulation. A printed PTMA has been realized by using the FR-4 printed circuit board substrate. The measured voltage standing wave ratio is less than 3 from 4 to 10 GHz. In the UWB communication frequency range, the measured phase distribution of the input impedance is quite linear and the H-plane patterns are almost omni-directional. The Kirchhoff's surface integral representation was adopted in the developed finite-difference time-domain code to compute the far field distributions from the near filed ones in time-domain. This is to investigate the radiated power density spectrum (PDS) shaping to comply with FCC emission limit mask. The effect of various source pulses (first-order Rayleigh pulses with /spl sigma/ of 20, 30, and 50 ps) on the radiated PDS shaping is also studied.     

Spectral domain analysis of wall admittances for circular and annular microstrip patches and the effect of surface waves

Wall admittances for circular and annular ring microstrip antennas have been determined, including the effect of the substrate. The magnetic current model is used and the analysis is carried out in Hankel transform domain. The final expressions for wall admittances are obtained in integral form. The contributions of the surface wave to the wall conductances have been determined by evaluating the integrals near the singularity using the singularity extraction technique. The radiation conductance has been determined by simple integration. The value of wall susceptance, obtained in this paper, agrees well with Kirchhoff's equivalent extension formula. A closed form expression for wall susceptance for theTM_{1n}mode has been obtained by curve fitting the numerical values. The effect of the substrate on wall admittance has been found to be significant for higher order modes and is shown to explain the measured input impedance of an annular ring microstrip antenna.     

表面波放电狭缝天线辐射电磁场的三维数值分析

针对平板型表面波放电等离子体源,建立了表面波放电狭缝天线辐射电磁波模型,对狭缝天线辐射电磁场分布进行了三维数值计算,并与表面波电磁场进行对比分析,讨论了平板型表面波放电机理。结果表明:整个狭缝天线阵激发的电磁场是每个狭缝天线激发电磁场的线性叠加;狭缝天线阵直接激发的电磁场强度在临近波导壁面处很大,并且随着空间距离的增大迅速衰减;狭缝天线阵直接激发和表面波的电场均远大于各自的磁场,分析电、磁场对带电粒子的力作用时可以忽略磁场力的作用;表面波电磁场远大于狭缝天线阵直接辐射的电磁场,强电磁场范围也远大于狭缝天线阵直接激发的强电磁场范围,等离子体有增强电磁场强度、扩大强电磁场范围的作用。     

Optimal Characteristics of an Arbitrary Receive Antenna

Several fundamental questions about the operation of receiving antennas are addressed, such as “Why does a receiving antenna scatter an incident field?” and “Under what conditions does a receive antenna capture all of the available incident power?” A new method is described by which the received power can be maximized for an arbitrary receiving antenna. The technique is first illustrated for two-dimensional infinite receiving arrays of electric and/or magnetic dipole elements, which result in simple plane waves for the scattered (re-radiated) fields. Optimal results (for maximum received power) are derived for several cases, and it is established that half the available incident power may be received by an array of electric (or magnetic) elements in free space, and that all available incident power may be received by an array that combines electric and magnetic elements, or one that incorporates a ground plane. Next, an arbitrary finite three-dimensional antenna enclosed by a mathematical spherical surface is treated using spherical vector wave functions. It is shown that half the available incident power can be received by such an antenna consisting of either TM or TE only elements, while all available incident power can be received when both TM and TE elements are used. It is also shown that the absorption efficiency for any optimal arbitrary antenna is 50%.      

Radiation characteristics of a source in a thin substrate mountedover a dielectric medium

The radiation pattern of a line source is calculated for the case in which the source is lying on the top or the bottom surface of a lossless dielectric substrate that is mounted on the top of semi-infinite dielectric medium. It is found that in both cases the pattern along the interfaces has a null; that the pattern in the upper semi-infinite medium has a single lobe; and that the pattern in the lower semi-infinite medium has many lobes, the number of which varies with the substrate thickness. In both cases, the power radiated into the lower medium is more than that radiated into the upper medium. Applications of this calculation to remote sensing, microstrip antenna technology, and antenna arrays are discussed     

High resolution three-dimensional microwave imaging of antennas

A procedure for imaging antenna currents that uses a relationship between the radiated far-field hemisphere and the Fourier transform domain of the source current density distribution is presented. The technique is applied to an array of two orthogonal waveguides, a slotted waveguide array and a reflector antenna. In each case the radiated far-field hemisphere is inverted to produce a high-resolution volumetric image of the antenna currents. Polarization discrimination is demonstrated as is the ability of the technique to `see behind' blockages by defocusing the foreground. It is shown that accurate distribution is available from the reconstructed image. Selective editing of the Fourier domain of the current distribution is performed to suppress unwanted artifacts in the reconstruction     

Shorted elliptical patch antennas with reduced surface waves on two frequency bands

In this paper, a study on the surface waves emission of a shorted annular elliptical patch (SAEP) antenna is presented. This radiator is constituted of an annular elliptical patch having the inner border shorted to the ground plane. The surface wave field excited by the SAEP antenna has been evaluated considering an equivalent magnetic current distribution flowing onto the outer boundary of the patch. It will be demonstrated that the dimensions of the outer elliptical contour can be chosen in such a way that the excitation of the TM/sub 0/ surface wave mode is suppressed on two frequencies. This characteristic makes possible the design of SAEP antennas with reduced surface wave (RSW) emissions on two frequency bands. To validate this result both numerical simulations and measurements will be presented. In particular, it will be shown that when the RSW-SAEP is considered the field strength within the substrate undergoes a faster decay resulting in a reduced mutual coupling in dual band array applications. Furthermore, the effective reduction of the surface waves power minimizes the scattering from the ground plane edges leading in smoother radiation patterns.     

时域天线阵列半功率波束宽度计算

对于冲击雷达系统中的时域天线阵列,提出点源近似模型,用来计算时域超宽带天线阵列辐射瞬态电磁脉冲的场方向图以及辐射波束的半功率波束宽度。采用点源近似模型计算的半功率波束宽度和CST仿真结果一致,并和实验测试结果吻合得很好。实验表明,阵列辐射瞬态电磁脉冲具有波束聚焦特性,点源近似模型可以作为一种简便的方法,对时域天线阵列的参数进行分析。     

Time domain analysis of patch antennas in a magnetized plasma bythe spatial network method

The near field of a patch antenna in a magnetized plasma is simulated by use of the spatial network method, which is a three-dimensional time domain simulation method. Two fundamental cases are examined in the radiated field: where the direction of the constant magnetic field is perpendicular to the patch plane, and where it is parallel. Results show that radiation characteristics of patch antennas in a magnetized plasma are different from those in free space. It was also confirmed that the Faraday effect is shown in the near field when a perpendicular constant magnetic field is applied to the antenna. In this analysis, the free boundary condition is approximated by terminating the volume with the free space characteristic impedance. A stricter model is necessary, if a reflectionless boundary is to be realized     

基于SIW的多波束CTS阵列天线设计

文中设计了一款基于基片集成波导(SIW)的毫米波高增益多波束连续横向枝节(CTS)阵列天线,它通过切换馈电端口实现多波束功能。该天线整体结构简单,采用印刷电路板工艺实现。天线主要包含馈电喇叭、平面波转换结构以及辐射结构三个部分,由三层基板构成。馈源为基于SIW的馈电喇叭,并在口径处添加匹配结构以提高其辐射性能;平面波转换结构由SIW抛物面和渐变耦合槽组成,可将馈电喇叭辐射出的柱面波转换为幅度服从泰勒分布的平面波进而为CTS阵列馈电,因此天线具有低副瓣的特性;辐射结构为1×8的CTS阵列,通过优化缝隙宽度以保证每个单元辐射出相等的能量。天线工作在30 GHz,通过切换馈电端口可在±20°范围内实现波束切换,天线测试结果与仿真结果吻合,验证了设计的合理性。     

Sub-THz Photonic-Transmitters Based on Separated-Transport-Recombination Photodiodes and a Micromachined Slot Antenna

We demonstrate a novel photonic transmitter, which is composed of a low-temperature-grown GaAs (LTG-GaAs)-based separated-transport-recombination photodiode and a micromachined slot antenna. Under femtosecond optical pulse illumination, this device radiates strong electrical pulses (4.5-mW peak power) without the use of a Si-lens. It can be observed in the Fourier transform infrared spectrometer spectrum of radiated pulses that a significant resonance, with a peak power of approximately 300 muW, occurs at 500 GHz, which corresponds to the designed resonant frequency of the slot antenna. The saturation problem related to the output terahertz power that occurs with the traditional LTG-GaAs-based photonic-transmitters when operated under high external applied electrical fields (>50 kV/cm) has been eliminated by the use of our device     

Network modeling of an inclined and off-center microstrip-fed slotantenna

This paper describes a general method for analyzing a microstrip-fed slot antenna with a view to developing an improved network model featuring an inclined and off-center slot. The network model consists of an ideal transformer, a radiation conductance, and extended slotlines terminated by short circuit. The transformer turn ratio can be calculated by combining the reciprocity theorem with the spectral-domain immittance approach. The radiation conductance is determined by the radiated power from the slot in the forms of space and surface waves in the spectral domain. Then network models corresponding to several variations of the antenna are described and the series impedances are computed. The computed results using the network model are compared with the rigorous solution and measurements and good agreements are obtained     

高频强场源对天馈系统的电磁耦合效应仿真

为获得天馈系统附近给定设备内部可能引起的电磁干扰的估计值,从而优化天馈系统的设计参数,采用COMSOL中的磁场模块,模拟完整天馈子系统在受到外部电磁场作用而激发出的电场强度和电流密度。模型空间采用无限元域截断,感应电流主要分布在天馈子系统固体的内外表面,其值一般在650 A/mm2左右,天馈子系统固体内部的感应电流小于6 A/mm2。对于壁面较薄的区域,固体内部的感应电流亦较大。仿真结果表明,天馈子系统对于外界辐射电磁源的偶合电磁效应主要集中在固体部分的表面,从而引起信号的改变,对误码率的作用较大。     

Transmitter-to-Antenna Power Transfer Under Unmatched Conditions

One phase of the electromagnetic compatibility program is the determianation of the electromagnetic energy actually radiated into space by an antenna. Methods have long been established, or proposed, for measuring the power output of a transmitter, the antenna impedance, and the antenna-radiation pattern. However, very little definitive work has been published regarding the methods for computing the transmitter energy coupled to the antenna and radiated at harmonic and spurious frequencies. It is the purpose of this paper to reduce to a simple form the equations for determining the power absorbed by an antenna connected through a coaxial transmission line to a transmitter. Most discussions of transmission-line-power transfer assume the matched conditions so universally desired at the operating frequency. When harmonic and spurious frequencies are considered, both the transmitter and the antenna are likely to be poorly matched to the transmission line and to each other. This paper points out what measurements need to be made and gives the functional relations necessary to compute the power radiated under unmatched conditions. Since the actual power coupled to the antenna in a given instance may be critically dependent upon the exact length of transmission line, some means must be available to take this into account. The expressions derived give the maximum and minimum power that will be absorbed, and also give the probability that any specified intermediate power will be exceeded if a random choice of transmissionline length is used.