CHARACTERISTICS OF CAVITY-BACKED NARROW SLOT ANTENNA IN A LOSSY MEDIUM

Cavity-backed slot antenna;Lossy medium;Moment method;Dyadic Green'sfunction     

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     

Analysis of hemispherical cavity-backed slot antenna

The input impedance of the hemispherical cavity-backed slot antenna is investigated theoretically and experimentally. The mode-matching method and moment method are used to find the Green's function of the cavity and the equivalent magnetic current of the slot, respectively. The effects of slot length and cavity radius on the input impedance are studied     

Size reduction of cavity-backed slot antennas

A technique for reducing the dimensions of the cavity of a cavity-backed slot antenna (CBSA) is presented, which facilitates proper fabrication and integration of miniaturized slot antennas on multilayer substrates. This is accomplished by replacing the solid metal around the traditional slot antennas with a specific metallic pattern that can be viewed as a series of parallel strip lines placed around the slot antenna. This metallic pattern is then modified by designing the parallel strips in a compact fashion to reduce the overall antenna dimensions and obtain a reduced-size CBSA. It is shown that, for a simple straight slot antenna, the overall occupied volume of the modified cavity backing the slot antenna can be reduced by more than 65% without affecting the high radiation efficiency of the antenna. A number of traditional cavity backed slot antennas and the proposed modified CBSAs are designed, fabricated, and measured. The reduced-size CBSAs show a very low input VSWR, low cross-polarized radiation levels, and high radiation efficiency. Despite their small ground plane size, the proposed cavity backed slot antennas have front-to-back ratio (FTBR) values in the range of 6-7 dB.     

General solutions of the narrow strip (and slot) integral equations

Analytic solutions of the integral equations for the current induced on a narrow conducting strip are obtained by two methods. One method follows from an expansion of the strip current in a series of Chebyshev polynomials while the other is based on a special power series expansion. In the former, Fourier-type coefficients, depending on integrals of the excitation, are derived while in the latter the coefficients depend upon derivatives of the excitation. From knowledge of the strip current simple expressions for the far-zone scattered field are derived. Explicit results are given for plane wave excitation. The solution methods apply to the equations for the narrow slot in a planar conducting screen.     

Analysis of a cavity-backed annular slot antenna with one pointshorted

Analysis of a cavity-backed annular slot antenna with one point shorted is performed experimentally and theoretically. Resonance frequencies, bandwidths, and radiation patterns are studied with respect to slot width, cavity depth, and slot shorting position. In the theoretical analysis, the method of moments is applied to find the magnet current on the slot, and the Green's function for the field inside the cavity has been newly derived. By selecting a slot shorting position, circular polarization, and a bandwidth of more than 10%, the voltage standing-wave ratio (VSWR) ⩽2 for the input impedance is obtained     

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.     

Experimental study of the impedance of cavity-backed slot antennas

The impedance of a simple open slot antenna was measured as a function of frequency and was then compared with the theoretical values obtained through Babinet's principle from the known values of the admittance of its complementary antenna, the strip dipole. A careful experimental study was then made of the impedance of the same slot with several different cavity backings. The impedance was found both as a function of frequency and of the various parameters of the cavity, namely, the cross-sectional size of the cavity, the medium filling the cavity, and the type of termination of the cavity.     

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     

Theoretical and experimental results of guided wavelength of a slot on a low-permittivity substrate

In the letter theoretical results for the guided wavelength and characteristic impedance of different slots are given for a substrate of relative permittivity ?r = 2.17. A formula is given for the first parameter. A comparison of theory and experiment, according to a model of a transmission-line applied to the slot, is presented.     

Theoretical modeling of cavity-backed patch antennas using a hybridtechnique

A hybrid technique that combines the method of moments (MoM) and the finite element method (FEM) to analyze cavity-backed patch antennas is presented. This technique features the use of FEM in solving the electromagnetic field distribution in the cavity and the use of MoM in solving integral equations outside the cavity. The results of MoM and FEM are combined through the continuity conditions on the boundary of the cavity. Due to the flexibility of FEM, complex cavities filled with inhomogeneous media can be analyzed by this technique. The results obtained by this hybrid technique are compared to the finite difference time domain (FDTD) results and good agreement is found     

Theoretical and experimental study of modified coupled strip coupler

A numerically efficient full-wave analysis of a modified coupled microstrip structure useful for the design of high directivity coupler sections is reported. The effect of the dispersion on the performance of the coupler is considered. An automatic design procedure has been implemented and experimental results are included.<>     

加载多层介质谐振器的宽带背腔缝隙天线设计

提出并设计了一种工作于X波段的新型宽带背腔缝隙天线,通过在缝隙外侧加载多层介质谐振器,有效扩展了天线带宽并显著提高了天线增益.设计的天线中心频率为10 GHz,-10 dB回波损耗带宽约为40％;带内增益5～9.5 dBi,比未加载多层介质谐振器的背腔缝隙天线提高2～3 dB.实测结果同设计结果基本吻合,有效验证了该设计的正确性.     

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 mathematical model for the impedance of the cavity-backed slot antenna

A mathematical model is derived that relates the impedance of a cavity-backed slot antenna to that of an identical slot which is free to radiate on both sides of a large ground plane. The model, which utilizes empirical constants from a previous experimental investigation, provides a continuously variable function of frequency and cavity depth for the impedance of a cavity-backed slot of fixed length and cavity cross section. This function is then compared with previously found experimental values and two theoretical solutions, one using a variational method and the other using the complex Poynting theorem.     

The method of induced magnetomotive forces for many-element cavity-backed slot radiators

The method of induced magnetomotive forces is used for solving the problem of distribution of equivalent magnetic currents in an antenna-waveguide structure of the “two-slot resonant diaphragm—rectangular resonator—radiating slot” type on the end face of a semi-infinite rectangular waveguide. The numerical and experimental investigations of this system are performed and the plotted electrodynamic characteristics are presented. Original Russian Text ? M. V. Nesterenko, V. A. Katritch, 2007, published in Izvestiya VUZ. Radioelektronika, 2007, Vol. 50, No. 4, pp. 68–76.     

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。     

The equivalent radius of a narrow conducting strip

By means of a simple and direct analytical procedure, it is confirmed that the equivalent radius of a narrow conducting strip is one-fourth its width. The analysis proceeds from the integral equation for the surface current density induced on a conducting cylinder of general cross section and its incorporates knowledge of the current density induced on a narrow strip. Explicit expressions are given for the total axial current induced on the narrow strip and for its echo width.     

Scattering by a narrow perfectly conducting infinite strip in a gyroelectric medium

The scattering of a plane electromagnetic wave of wave-numberkby a perfectly conducting infinite strip of width2ais investigated for the case in which the surrounding medium is gyroelectric. The gyroelectric axis is assumed to be parallel to the edges of the strip. The problem is formulated in terms of an integral equation whose solution is obtained in the form of a series in powers ofka. Expressions for the far-zone fields and the first two terms in the series for the total scattering cross section are obtained.     

Measurement of electromagnetic fields near a monopole antennaexcited by a pulse

To observe transient radiation fields, a technique for reconstructing electromagnetic (EM) waveforms using the complex antenna factor (CAF) have been developed. However, the CAF is originally defined assuming plane wave incidence, while the waveforms are measured in a vicinity of the radiating source. In order to examine the reconstruction technique using the CAF in the near-field measurements, the EM fields radiated from a monopole antenna excited by pulsed input voltage was reconstructed and compared with calculated results. For the geometry of the experiment, the waveforms of the reconstructed and calculated EM fields have shown good agreement. Therefore, the reconstruction technique using the CAF can be used for similar dimensions or at a greater distance when sufficient sensitivity is provided