Design of cavity-backed slot antennas using the finite-differencetime-domain technique

A cavity-backed slot antenna is thought to be one of the most suitable elements for the wireless transmission of microwave energy. A design technique is developed for the cavity-backed slot antenna using the finite-difference time-domain (FDTD) method. The technique is effective in characterizing antenna performance such as the input impedance and the far-field pattern since it takes into account the geometry of the feeder as well as the cavity. We present a method that overcomes difficulties when the FDTD method is used to design the antenna. Moreover, we discuss how to determine the calculation parameters used in the FDTD analysis. Several numerical results are presented, along with measured data, which demonstrate the validity, efficiency, and capability of the techniques. The paper proposes a new prediction method for the frequency characteristics of the cavity-backed slot antenna, which applies computational windows to time-sequence data. It is emphasized that windowing the slow decaying signal enables the extraction of accurate antenna characteristics. We also discuss how to estimate the antenna patterns when we use a sinusoidal voltage excitation     

An Efficient FDTD Model for Resistively Loaded Cylindrical Antennas With Coaxial Lines

A full coarse-grid based finite-difference time-domain (FDTD) model is proposed for an efficient analysis of resistively loaded cylindrical antennas driven by coaxial feed lines. In the case of the electrically thin resistive antenna, the thin-wire approximation is applied to the near fields around the antenna. The resistive antenna is equivalently represented by a series connection of piecewisely lumped resistors along the antenna axis. And the coaxial line is replaced by an equivalent source over the feed aperture of the line. Then the corresponding FDTD update equations make it possible to implement the full coarse-grid model without additional grid refinements for the antenna and the feed line. The transient reflected feed voltage and the input impedance of resistive antennas are calculated numerically and compared with those of a full fine-grid.      

Low Profile Miniaturized Planar Antenna With Omnidirectional Vertically Polarized Radiation

A novel miniaturized cavity-backed composite slot loop antenna (CBCSLA) with low profile and omnidirectional radiation similar to a short dipole is presented. The antenna displays vertical polarization while having less than lambda/100 dimension in height. The geometry of the antenna is inspired from a small magnetic loop which is realized using a slot configuration on metallic ground. Since a small slot loop antenna cannot be impedance matched, a composite geometry is devised that acts like as a small slot loop and can easily be impedance matched using this configuration. The diameter of the CBCSLA can be made as small as lambda/10 or smaller. The feeding mechanism is designed in a manner to create a circumferentially-constant current distribution around the composite loop while effectively matching to a 50 Omega coaxial feed from the antenna center. Additional methods are discussed to further enhance the bandwidth and achieve a dual-band response. The antennas are designed, fabricated, and measured. It is shown that despite their small lateral dimension and extremely small height, the miniaturized cavity-backed slot loop features extremely well input impedance match, uniform radiation pattern, low cross-polarization levels and expected gain.     

应用于Wi-Fi频段的背腔式缝隙天线设计

采用波导反射模型分析了背腔深度对缝隙天线辐射特性的影响, 通过仿真计算, 确定了当背腔深度等于四分之一波导波长时, 金属背腔会使缝隙天线的输入电阻加倍, 但对输入电抗产生影响较小, 根据以上仿真结果, 提出了一种有效的背腔式缝隙天线的输入阻抗电路模型, 分析了馈电位置和缝隙长度对天线谐振点的影响, 为缝隙天线的多频点设计提供了理论依据.结合仿真工具, 设计了两类工作于Wi-Fi频段的背腔式缝隙天线:第一类天线工作于室外2.4 GHz频段; 第二类天线可以同时工作于2.4 GHz和5.2 GHz频段.最后, 对天线的S₁₁系数进行了实测, 实测与仿真结果基本一致.     

A simple feed model that reduces time steps needed for FDTD antennaand microstrip calculations

The finite-difference time-domain (FDTD) method is being widely applied to antenna and microstrip calculations. One aspect of this application is accurately and efficiently modeling antenna and microstrip feeds within the constraints of the FDTD approximations. Several relatively straightforward approaches have been suggested, including gap and frill feeds. More complicated approaches, which involve including the coaxial feed cable in the FDTD calculation space, have also been suggested. A related aspect is the desirability of reducing the number of time steps required for the FDTD calculations to converge, especially for transient excitation. We illustrate that for many geometries a simple gap model with an internal source resistance provides accurate results while greatly reducing the number of time steps required for convergence     

背腔式窄缝天线在有耗介质中的特性

本文利用矩量法与并矢格林函数相结合,研究了背腔式窄缝天线在有耗介质中的特性。对于矩阵单元的双重级数,采用泊松求和公式改善了级数的收敛性;对于矩阵单元的二重积分,分别采用积分中值定理及椭圆积分予以简化。本文的数值结果分别给出了有耗介质及天线结构参数对输入阻抗的影响,为天线设计提供了依据。     

微带线-槽线馈电缝隙等角螺旋天线设计

被动雷达导引头为探测与跟踪目标可采用宽带等角螺旋天线,针对降低等角螺旋天线剖面,该文提出一种低剖面背腔式微带线-槽线馈电缝隙等角螺旋天线。微带线-槽线巴伦(Balun)中渐变微带线将同轴线激励的不平衡电场最终转化为槽线处平衡电场。实测结果表明,该缝隙等角螺旋天线实现了1:9的电压驻波比(VSWR)带宽,良好的辐射方向图与圆极化特性。在天线背面加入高度仅有0.05L(L为最低工作频率所对应自由空间中波长)的反射腔,腔内放置矩形环状吸波材料,有效拓展了天线低频段带宽。测试结果表明带有反射腔的缝隙等角螺旋天线实现了1:6.4的电压驻波比带宽,天线增益大于4 dB,良好的圆极化与方向图特性。平面化、一体化的馈电方式与低剖面反射腔有效降低了缝隙等角螺旋天线剖面,测试结果验证了该文所提出的微带线-槽线巴伦馈电缝隙等角螺旋天线设计方法的有效性。     

Optimization of bow-tie antennas for pulse radiation

Resistively loaded bow-tie antennas are considered as radiators for temporally short, broad-bandwidth pulses. Analysis is by the finite-difference time-domain (FDTD) method. The geometrical details of the antenna and the resistive loading along the antenna are chosen to optimize this antenna for pulse radiation. Theoretical results for the reflected voltage in the coaxial feed line and the time-varying radiated electric field are compared throughout with experimental measurements. The optimized, resistive bow-tie antenna is shown to radiate a pulse that more closely resembles that of the excitation than is radiated by a metallic bow tie of comparable size. Issues involving the use of the FDTD method for modeling fully three-dimensional antennas are also discussed. These issues include the use of a simple feed model and the staircasing of the edges of the antenna     

Radiation of High-Gain Cavity-Backed Slot Antennas Through a Two-Layer Superstrate

The radiation of cavity-backed slot (CBS) antennas through a two-layer superstrate is studied in this paper. A novel transmission-line model is proposed to explain the gain-enhancement effect of the superstrate on cavity-backed slot antennas. Experimental result showed that a single cavity-backed slot antenna can achieve a high gain of 16.7 dBi through a properly designed superstrate, and this gain-enhancement property is valid for array configurations, as well. A rotationally arranged four-slot array, covered by the superstrate, is also investigated, to demonstrate that good circular polarization and high gain can be obtained from the superstrate-covered slot antennas.     

Theoretical and experimental study of the input impedance of thecylindrical cavity-backed rectangular slot antennas

The authors study the input impedance of a cylindrical cavity-backed slot antenna based on mode matching and the complex Poynting theorem. Two cavity-backed slot antennas were fabricated to verify the theory. The numerical results agree very well with measurements. Two resonant frequencies were found from the input impedance. One resonant frequency is attributed to the rectangular slot and the other is due to the cavity. The slot length controls the first resonant frequency and has a much stronger effect on the input impedance at the antenna operating frequency as compared with the cavity length     

一种新型 SIW 背腔缝隙天线的研究

介绍了一种新型基片集成波导背腔六边形缝隙线极化天线。背腔缝隙天线是一种技术成熟的天线类型,但是笨重的体积限制了传统金属腔体缝隙天线的发展。基于基片集成波导结构的背腔缝隙天线以其低损耗、高功率容量、高增益 以及易集成等诸多优点而备受关注。文中设计了一款基于基片集成波导加开六边形缝隙的背腔天线,通过CST软件仿真,并制作了天线实物进行测试。天线的中心工作频率为10 GHz,增益为4. 87 dB,带宽为147 MHz。     

Network model for strip-fed cavity-backed printed slot antenna

An equivalent network for the strip-fed cavity-backed slot antenna is derived. The model is based on some physical insight into the problem. The various parameters of the network are derived from the experimental data on the input reflection parameter of the antenna. This model gives an insight into the strip-slot-cavity coupling and hence the working of the structure. It is also useful for predicting the performance of such practical antennas.     

Theory and experiment of the hemispherical cavity-backed slotantenna

The hemispherical cavity-backed slot antenna is studied theoretically and experimentally. The exact magnetic field Green's function of the cavity is derived rigorously and expressed in a form convenient for numerical computation. The moment method is used to find the equivalent magnetic current in the slot and, hence, the input impedance of the antenna configuration. The effects of the cavity size, of the slot length, and of the slot offset on the input impedance are studied and very good agreement between theory and experiment is obtained. The variation of the magnetic current around the slot and cavity resonances are discussed. Comparisons between the rigorous solution and the single-mode theory are given and the limitation of the single-mode theory is discussed     

背腔式槽阵的谱域法

本文运用谱域法和传输线概念建立背腔式槽阵的本征方程，在窄槽情况下，与文［３］的本征方程相同。导出天线基本参数如功率传输系数，输入电压驻波比。品质因素，辐射场以及方向性系数的表达式，并以功率传输系数为例进行了数值计算。     

The input admittance of the rectangular cavity-backed slot antenna

The input admittance of the rectangular cavity-backed slot antenna is investigated. The slot is assumed narrow so that the voltage distribution in its aperture is sinusoidal. Equations which represent the input admittance of this slot, backed by a rectangular cavity in which a single propagating wave is assumed to exist, are given. Calculations based on these representations are compared to available measured data. As the depth of the cavity increased the resonant frequency decreased and the bandwidth became narrower. Input admittance curves as a function of electrical slot length are also presented for several size cavities.     

SIW cavity-backed circularly polarized square ring slot antenna with wide axial-ratio bandwidth

In the proposed work, Substrate Integrated Waveguide (SIW) cavity-backed circularly polarized slot antenna for wideband operation is proposed. A square-ring-slot is etched on the top of the SIW cavity, used for radiation To generate the circularly polarized (CP) wave, the slot is placed slightly offset from the centroid of the cavity. By finely optimizing the antenna dimensions, it exhibits a wide axial-ratio (AR) bandwidth of 789 MHz (7.1%) ranging from 10.64 to 11.45 GHz. Moreover, the radiating slot is excited by an SIW based feed by an inductive window, which lead to a wide impedance matching over 1.74 GHz ranging from 9.92 to 11.67 GHz. Due to the SIW cavity-backing structure, the antenna offers unidirectional radiation patterns while maintaining a low-profile and planar compatibility. To validate the proposed design, the antenna is fabricated and experimentally tested in terms of reflection coefficients, AR, gain, and radiation patterns. The simulated and measured results reveal good mutual agreement. Moreover, the proposed antenna is very useful for wideband applications operating in X-band (8–12 GHz)     

小型化八边形基片集成波导背腔缝隙天线

提出一款新颖的W波段八边形基片集成波导(SIW)背腔缝隙天线。相较传统的缝隙天线，具有体积小、易加工、Q值高、成本低等优点，且易于成阵。通过调节天线背腔缝隙的长度、宽度，以及SIW腔体的尺寸优化天线的辐射特性，通过电磁仿真软件HFSS对模型进行仿真优化，确定了天线的最优结构。仿真实验结果表明，所设计的天线相对带宽约4.5%，方向性优良，中心频率点谐振深度<-31 dB，天线最大增益达到5 dBi，满足设计要求，验证了设计的正确性。所设计的SIW背腔缝隙天线拓宽了数字通信的可用频谱，是一种新的尝试，可为以后的研究提供新的参考思路。     

A note on the impedance variation with feed position of a rectangular microstrip-patch antenna

The variation with feed position of the input impedance of a rectangular patch antenna is investigated theoretically. Two different feed types are examined: an inset microstrip line, and a coaxial probe. The finite-difference time-domain (FDTD) technique is used for the calculations. Numerical results are compared with published measurements and other theoretical models.     

Analysis of the open-ended image NRD guide using FDTD

Simulation is an indispensable means of designing antennas, especially when the evaluation of the antenna characteristics using theoretical analysis is complex or not very accurate. This work proposes an open-ended image nonradiative dielectric (NRD) guide antenna and presents its characteristics obtained using the finite-difference time-domain (FDTD) method. The key features of the FDTD implementation are discussed, particularly the simple and convenient approximate three dimensional modeling of the coaxial feed cable and the excitation probe that were used. The characteristics of the antenna that were determined are the return loss and absolute gain frequency characteristics and the E- and H-plane radiation patterns. Experimental results are used to verify the characteristics obtained using FDTD and are found to be in good agreement.     

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.