Theory and Experiment of an Aperture-Coupled Hemispherical Dielectric Resonator Antenna

A hemispherical dielectric resonator (DR) antenna using aperture coupling for excitation is studied both theoretically and experimentally. The reciprocity method is used to formulate the problem. The exact magnetic field Green's function due to the equivalent magnetic current in the slot is derived rigorously, and it is presented in a form which can be evaluated very efficiently. Moment method is used to solve the magnetic current from which the input impedance of the antenna configuration is obtained. The equivalent radius of the slot is used so that simple formulae developed for the cylindrical dipole can be applied directly. The effects of the slot's length, the slot's position, and the slot's width on the broadside TE₁₁₁ mode input impedance are studied, and reasonable agreement between theory and experiment is obtained     

一种适用于波束扫描的宽带低剖面介质谐振器天线

近年来,为解决传统介质谐振器天线（dielectric resonator antenna, DRA）体积庞大等问题,新颖的低剖面DRA如介质贴片天线和平面介质天线被提出并迅速成为研究热点. 然而,现有的低剖面DRA设计要么平面尺寸较大（>0.5λ₀×0.5λ₀）,要么带宽较窄（<10%）,限制了它们的实际应用. 文中提出了一种具有小型化平面尺寸的宽带低剖面DRA. 本天线采用介质贴片设计,顶部为高介电常数的介质贴片,中间为低介电常数的介质基板,底部为缝隙馈电结构. 缝隙馈电结构可激励起介质贴片谐振器的基模TE₁₁₁和高次模TE₁₃₁两种工作模式,这两种模式的场分布在贴片边缘部分存在基模场强较弱而高次模场强较强的显著区别. 本设计巧妙地利用了该区域的模式场强区别,通过略微增加贴片边缘部分高度来显著影响高次模谐振频率而轻微影响基模谐振频率,从而将高次模TE₁₃₁的谐振频率迅速下拉并与基模TE₁₁₁的谐振频率靠近合并,在不增大介质贴片平面尺寸的前提条件下获得宽带工作效果. 本天线的三维尺寸为0.35λ₀×0.35λ₀×0.08λ₀ (λ₀为中心频率处的空气中波长),线极化实物案例测试结果表明该天线具有18.5%的?10 dB阻抗带宽以及7.3 dBi的最大增益. 该天线平面尺寸小,适用于具有波束扫描功能的阵列天线设计;且提出的设计理念还可进一步拓展应用于圆极化天线设计.     

Analysis of dielectric-resonator antennas with emphasis onhemispherical structures

An overview is given for the development of dielectric-resonator antennas. A detailed analysis and study of the hemispherical structure, excited by a coaxial probe or a slot aperture, is then given, using the dyadic Green's functions pertaining to an electric-current source or a magnetic-current source, located in a dielectric sphere. The integral equation for a hemispherical dielectric-resonator antenna (DRA), excited by either a coaxial probe or a slot aperture, is obtained. The integral equation is solved using the method of moments. The antenna characteristics, such as input impedance, radiation patterns, directivity, and efficiency, are computed numerically, around the resonant frequency of the TE₁₁₁ mode (the HEM₁₁ mode for cylindrical coordinates). The computed input impedance is compared with numerical and experimental data available in the literature     

FDTD analysis of probe-fed cylindrical dielectric resonator antenna

The finite-difference time-domain (FDTD) method is employed to analyze a probe-fed cylindrical dielectric resonator antenna. Numerical results for the input impedance and radiation patterns of the dielectric resonator (DR) antenna operating in HEM_11δ mode are presented and compare favorably with measurements. The effects of various parameters on the characteristics of the DR antenna are studied. Fabrication imperfection effects and the cross-polarization characteristics of this type of DR antenna are also investigated for the first time     

Complex resonance and radiation of hemisphericaldielectric-resonator antenna with a concentric conductor

The probe-fed hemispherical dielectric-resonator antenna (DRA) with a concentric conductor is studied theoretically in this paper. Using the mode-matching method, the exact Green's functions for evaluation of the input impedance and radiation patterns are found, with the functions presented in computationally efficient forms. The moment method is used to determine the probe current and, hence, the input impedance as well as the radiation patterns. The results are verified by special cases available in the literature. In this paper, the effects of the conductor radius, dielectric constant, probe length, and probe displacement on the input impedance are investigated. The theory is very general and, by taking appropriate limits, can be used to study the solid DRA and the conductor-loaded wire antenna. To aid the DRA design engineer, the TE₁₁₁-mode characteristic equation of the DRA is also studied, from which the simple formulas for the resonant frequency and Q-factor are obtained     

FDTD analysis of probe-fed cylindrical dielectric resonator antennaoperating in fundamental broadside mode

An analysis of a cylindrical dielectric resonator antenna operating at the fundamental broadside mode using the finite-difference time-domain (FDTD) method is presented. Good agreement between theoretical and experimental results on the input impedance of the DR antenna is obtained. The effects of the probe length, feed position and the dielectric constant on the input impedance are presented     

Novel Microwave Network for the Leaky-Wave Analysis of Evanescent Fields in Stub-Loaded Structures

In this paper, a new transverse equivalent network for the modal analysis of stub-loaded leaky-wave antennas is developed. The derived network is useful for the study of the radiation of evanescent fields that occurs when they reach the top aperture of the parallel-plate stub. This transverse network is based, for the first time, on a nonhybrid formulation of the constituent parallel-plates modes of order 1 (TE₁ ^Z and TE₁ ^Z ). The obtained network is an alternative to the one based on hybrid TE₁ ^Vand TE₁ ^V modes, and leads to a simpler transverse resonance equation. The new equivalent network is validated by obtaining leaky-mode dispersion curves for a previously studied leaky-wave antenna in non- radiative dielectric guide technology.     

The input impedance of a coaxial line fed probe in a cylindricalwaveguide

Dyadic Green's functions for determining the electric and magnetic fields in a cylindrical waveguide due to a radially directed infinitesimally short electric dipole are derived. The waveguide is shorted at one end and terminated at a perfectly matched load at the other. Both TE and TM modes are considered. Based on these dyadic Green's functions, the input impedance of a coaxial line fed probe in front of the plunger is derived. The formula is expressed in a closed form. Excellent agreement between theoretical results and experimental data for exciting the TE₁₁ mode in the X band for various probe positions is observed     

On the Differentially Fed Rectangular Dielectric Resonator Antenna

A differentially fed rectangular dielectric resonator antenna (DRA) is studied using the finite-difference time-domain (FDTD) method. The fundamental TE₁₁₁ mode of the rectangular DRA is excited at 2.4 GHz, with a 10-dB differential impedance bandwidth (|S_dd11| < -10 dB) of ~10.4%. To verify the theory, measurements were carried out, and reasonable agreement between theory and experiment is obtained. The effects of the magnitude and phase imbalances on the DRA impedance and radiation pattern are investigated.     

Effect of fabrication imperfections for ground-plane-backeddielectric-resonator antennas

Results of numerical and experimental studies, pertaining to the effect of imperfections such as surface roughness, which could lead to poor mechanical contact between a dielectric resonator and the conducting surfaces on which it resides, are presented. This work simulates the poor-contact effect by introducing air gaps between the dielectric resonator (DR) and the adjacent conducting surfaces. Results are presented which illustrate the effect of air gaps upon the input impedance and resonant frequency of cylindrical-DR antennas, operating in the TM₀₁ and HEM₁₁ modes. Also presented are preliminary results pertaining to the validity of the thin-wire-theory approximation that is used in numerical electromagnetic design codes, to model the coaxial-feed probes, and results pertaining to the effect of an infinite-ground-plane assumption     

Cylindrical cavity-backed suspended stripline antenna-theory andexperiment

The problem of a cylindrical cavity-backed suspended stripline (SSL) antenna is viewed as a transition of the SSL to a circular cylindrical waveguide opening into an infinite ground plane. The fields in the waveguide are expanded in terms of TE and TM modes. The effect of the radiating aperture on the modal expansion of the fields is taken into account by introducing reflection coefficients for each mode. The current on the SSL probe is assumed to have sinusoidal distribution. These simplifications reduce the original problem to that of a known radially oriented current residing on a dielectric sheet inside a circular-cylindrical cavity whose top wall has known impedances corresponding to different modes. The Green's function for this modified structure is found and is used to obtain a general expression for the input impedance. This expression is specialized to the case where the SSL probe and the radiating aperture are coupled through the dominant TE ₁₁ mode only. This input impedance is translated to the measurement plane of the antenna. The computed and measured results are found to be in good agreement     

Reflector spillover loss of an open-ended rectangular and circularwaveguide feed

An important and frequently used parameter in the design of a feed for a reflector antenna is the spillover loss. A set of spillover curves is presented for several common feeds, namely circular waveguides with TE₁₁ or TE₂₁ excitations, rectangular guides for the monopulse application, etc. The difference between two common methods of normalizing the feed input power is also discussed     

Analysis of spherical annular microstrip antennas

The spherical annular microstrip antenna is analyzed. The antenna is excited by a coaxial line. The general transmission line model (GTLM) is used to compute the input impedance. The radiating TM₁₂ mode is considered because of its wide band. The effect of the other radiating modes and the nonradiating modes on the TM₁₂ mode is investigated. The effect of different parameters on the input impedance is considered. The radiation patterns are computed using the method of moments     

FDTD simulation of radiation characteristics of half-volume HEM and TE-mode dielectric resonator antennas

Cylindrical and rectangular dielectric resonator antennas (DRAs) using HEM_11δ, TE_11δ, and TE_01δ mode were examined to see the radiation pattern, impedance, field distribution and resonant frequency that were achieved when the DRAs were bisected through an image plane by a conducting sheet. The resultant half DRAs are smaller in volume and have a more directional radiation pattern. The elevation angle of maximum radiation was lowered in some cases. Finite-difference time-domain simulation techniques were used     

A millimeter-wave omnidirectional dielectric rod metallic gratingantenna

A new millimeter-wave omnidirectional dielectric rod metallic grating antenna is investigated theoretically and experimentally, in this paper. The radiation characteristics of the antenna are carefully investigated by a rigorous formulation for the TE₀₁-mode and TM₀₁-mode excitation in the Ka-band frequency range. Based on the analysis, an omnidirectional antenna excited by the TE₀₁ mode is designed and measured. The measured results are compared with theoretical predictions and good agreement is found. Extensive numerical results are given to establish some useful guidelines for the design of the omnidirectional antenna     

Study of TE0 and TM0 modes in dielectricresonators by a finite difference time-domain method coupled with thediscrete Fourier transform

An application of a numerical method of finite differences in the time domain (FDTD) coupled with the discrete Fourier transform is presented to determine the resonant frequencies of the TE₀ and TM₀ modes of axially symmetric dielectric resonators closed in a cavity. The technique is conceptually and computationally simple, and it allows access at once to information on the entire modal spectrum by means of the fast Fourier transform (FFT) applied to the time series. The cylindrical cavity dielectrically loaded at the base and the resonant frequency of the TE_01δ mode are analyzed in two systems: a cylindrical cavity with a cylindrical dielectric resonator of variable radius, and the shielded dielectric resonator on a microstrip substrate. The results obtained are compared with the rigorous (exact) theoretical solutions and with experimental results     

Input impedance of a probe-fed circular microstrip antenna with thick substrate

A method of computing the input impedance for the probe fed circular microstrip antenna with thick dielectric substrate is presented. Utilizing the framework of the cavity model, the fields under the microstrip patch are expanded in a set of modes satisfying the boundary conditions on the eccentrically located probe, as well as on the cavity magnetic wall. A mode-matching technique is used to solve for the electric field at the junction between the cavity and the coaxial feed cable. The reflection coefficient of the transverse electromagnetic (TEM) mode incident in the coaxial cable is determined, from which the input impedance of the antenna is computed. Measured data are presented to verify the theoretical calculations. Results of the computation of various losses for the circular printed antenna as a function of substrate thickness are also included.     

Integration equation analysis on resonant frequencies and qualityfactors of rectangular dielectric resonators

In this paper, the resonance problem of rectangular dielectric resonators (DRs) is analyzed by using the spectral dyadic Green's function and volume integral-equation formulation. The rectangular dielectric body is replaced by a set of entire-domain polarized volume current basis, and Galerkin's moment method is used to solve the resonant frequency and quality factor of the rectangular DR. The effects of electrical and geometrical parameters on the resonance of the TE₁₁₁ mode of isolated DRs are also presented. Additionally, the case of a rectangular DR with a ground plane is also discussed. Results are found to be in good agreement with the published experimental data     

Propagation of infrared radiation in hollow microstructuralcylindrical waveguides

Theoretical and numerical results are presented on the propagation of infrared radiation in TE₀₁-, TM₀₁-, and TE₁₁-like modes in an empty cylindrical, gold-coated waveguide of micron dimensions. Low-loss propagation is possible for the TE₀₁-like mode, whose configuration is similar to that of the TE₀₁ mode in a guide with perfectly conducting walls. Propagation is more lossy for the TM₀₁- and TE₁₁-like modes. While for small guide radii these modes resemble the TM₀₁ and TE₁₁ modes in a guide with perfectly conducting walls, they transform into surface waves as the guide radius is increased, with losses that are independent of guide radius     

Input impedance and mutual coupling of rectangular microstrip antennas

A moment method solution to the problem of input impedance and mutual coupling of rectangular microstrip antenna elements is presented. The formulation uses the grounded dielectric slab Green's function to account rigorously for the presence of the substrate and surface waves. Both entire basis (EB) and piecewise sinosoidal (PWS) expansion modes are used, and their relative advantages are noted. Calculations of input impedance and mutual coupling are compared with measured data and other calculatious.