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     

A numerical study of a dielectric disk antenna above groundeddielectric substrate

An antenna made of a dielectric disk with a high permittivity mounted on top of a grounded dielectric substrate of low permittivity is analyzed. A numerical procedure based on surface integral equations, derived from the equivalence principle, is used to compute the natural resonant frequencies for the HEM₁₁ mode from which the radiation Q factor of the antenna is obtained. Then the radiation pattern of the antenna, operating at the resonant frequency evaluated previously, is computed with an electric dipole excitation located within the dielectric substrate under the dielectric disk. The effect of various parameters on the radiation characteristics of the antenna is studied, and presented in the form of diagrams. The low values of the radiation Q, combined with the high values of the dielectric Q and conductor Q, indicate that this antenna promises to be more efficient then the microstrip antenna     

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     

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     

Theoretical and Experimental Study of a Novel H-Guide Transverse Slot Antenna (Short Papers)

Transverse slots in the "upper" plate of a dielectric-loaded parallel plane waveguide (H-guide) operating in the dominant mode (zero cutoff frequency) are proposed as slot antennas. A new theoretical approach to the analysis of a single-slot antenna is presented, leading to explicit expressions for the antenna input impedance and radiation efficiency. The computed values of the VSWR and radiation efficiency are in good agreement with laboratory measurements. The radiation efficiency of a single slot exceeds 10 percent in the 8-11-GHz frequency band, reaching a 50-percent theoretically predicted maximum at the slot resonance frequency, when the guide is terminated by a matched load. Experimental checks prove that the leakage, or parasitic, radiation power level is less than -40 dB relative to the measured radiated power.     

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     

Broadband U-shaped dielectric resonator antenna with elliptical patch feed

A dielectric resonator antenna formed by a U-shaped dielectric resonator and a conformal elliptical patch feed is proposed for wideband communication applications. Simulated results agree well with measured ones, showing good performance in terms of bandwidth and radiation patterns. The measured impedance bandwidth of S₁₁ < -10 dB is about 72%, covering the frequency range 3.82-8.12 GHz. It has a gain of 4.3-7.6 dBi over the whole operating band with a ground size of about 1.2 lambda₀ times 1.2 lambda₀, lambda₀ being the central operating frequency.     

Radiation and leakage characteristics of transverse slot inNRD-guide operating in LSE00 mode

Characteristics of a transverse slot in the upper plate of a nonradiative dielectric guide operating in the dominant LSE₀₀ mode have been analyzed. A fundamental radiation phenomenon due to the open property of the guiding structure is observed theoretically. It is found that the propagation direction of the leakage covers the whole angular spectrum in the plane parallel to the metallic plates. An explanation to its physical existence is given. A simple, but efficient method is developed to determine its angular power density. Numerical computation shows that the leakage is substantially high when the slot is near resonance     

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     

基于多模谐振的低剖面宽带贴片天线

为了增加贴片天线的工作带宽和改善其辐射特性,提出了一种基于多模谐振的低剖面贴片天线。通过在矩形贴片的非辐射边加载短路壁降低H面的高交叉极化,在贴片下方加载短路销钉提高TM_1/2,0模式的谐振频率（f_1/2,0）;然后在TM_3/2,0模式的零电流位置处切割一个矩形缝隙来激发辐射缝隙模式（TM_RS）,得到低剖面、宽频带和低交叉极化的三模谐振贴片天线;最后通过增加贴片宽度和调整天线结构,降低TM_1/2,2模式的频率（f _1/2,2）,实现了四模谐振。仿真和实测结果表明该四模谐振贴片天线在0.03λ₀的厚度下可将带宽增加到21.7% (2.67～3.32 GHz).     

Surface wave excitation on a microstrip ring antenna

A theoretical analysis of the excitation of surface waves on a microstrip ring antenna is presented. The problem is formulated using dyadic Green's functions in a layered medium with magnetic-type equivalent current sources. The integral equation for the fields is solved in the wave number complex plane so that the fields from space and surface waves are obtained separately. The space wave radiation efficiency is calculated for the TM₁₁, TM₁₂, and TM₁₃ modes for various values of the normalized dielectric substrate thickness, d/λ₀. It is noted that the TM₁₃ mode radiates more efficiently than the TM₁₁ and TM₁₂ modes. The results are of importance in the design of these antennas     

Effect of air gap on cylindrical dielectric resonator antenna operating in TM/sub 01/ mode

The results of a numerical study on the effect of an air gap on the input impedance and resonance frequency of a cylindrical dielectric resonator (CDR) antenna operating in the TM/sub 01/ mode as a function of dielectric constant are presented. The CDR resides on a conducting ground plane and is excited by a coaxial probe through the bottom of the ground plane. Some of the numerical results are validated experimentally.<>     

A compact dual band-notched UWB circular monopole antenna with parasitic resonators

A compact dual band-notched Ultra-wideband (UWB) circular monopole antenna that has two parasitic resonators in the ground plane is presented in this paper. The Inverted–U and Iron shaped parasitic resonators are located on the back side of the radiating patch to achieve the band rejection characteristics from 5 to 5.4 GHz for WLAN and 7.8 to 8.4 GHz for ITU band respectively. By cutting a rectangular slot on the ground plane, additional resonance is excited at the higher frequency band, and hence much wider impedance bandwidth can be attained. Applications of the proposed dual band-notched ultra-wideband (UWB) antenna structure with 5.2 GHz and 8.2 GHz center frequencies are demonstrated experimentally. Measured and simulated results of the magnitude of S₁₁, radiation patterns and realized gains show good agreement.     

The mode features of an ideal-gap open-ring microstrip antenna

A rigorous analysis of the features of the modes of an ideal-gap open-ring (closed ring with a cross cut) printed microstrip antenna is presented. General expressions for its radiation field are derived by using the cavity model, trigonometric identities, and the properties of the cylindrical functions. The solution and the computed results for the radiation patterns and the field distributions for the even and odd modes are presented. The solutions for the even modes are the same as those for the closed-ring printed microstrip antenna. The results for the radiation patterns and other antenna characteristics for the odd modes indicate the superiority in the radiation properties of the ideal-gap open ring when excited in the TM₁₂ mode over those of a closed ring     

Characteristics of aperture-coupled rectangular dielectricresonator antenna

Theoretical analysis of an aperture-coupled rectangular dielectric resonator antenna is presented. A model based on the modal expansion method and the spectral domain approach is developed. Numerical results for return losses and radiation patterns of the TE₁₁₁^y mode are compared with experimental data available in the literature and reasonable agreement between theory and experiment is obtained. This model is flexible as it enables studies to be made of the effects of parameters such as slot dimensions, slot displacement and stub length on input impedances     

Q-factor computation of radiation loss corresponding to surfacewave in a patch circular resonator

The authors present a new approach for the Q-factor computation of radiation loss in a circular patch with surface wave TM₀. The circular patch resonant frequency (f) problem is formulated in terms of an integral equation using the transverse resonance method. First, the computed real part of f is found to compare closely with the published results considering space wave TM₁₁. Next, the Q-factor of the surface wave as a function of physical resonator parameters is presented     

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     

Circularly polarised dielectric resonator antenna excited byperturbed annular slot with backing cavity

The circularly polarised dielectric resonator antenna excited by a perturbed annular slot is investigated experimentally. A backing cavity is placed beneath the slot to block undesirable backside radiation. The effects of varying the slot on the return loss and axial ratio are discussed. The radiation patterns and antenna gain of the configuration are also presented     

Propagation and radiation characteristics of dielectric loaded corrugated dual-frequency circular waveguide horn feeds

Based on a systematic analysis the design and experimental studies on a composite dual-frequency feed with a single radiating aperture are presented. The criterion for selecting the ratio of the diameter of the corrugated guide excited at the lower frequency in the dominant mode to that of the dielectric rod, axially located within the guide and excited at the higher frequency in the dominant mode, is discussed. The constructional features of a typical dual-frequency feed designed for operation atSandXbands (with 2.68 GHz and 9.375 GHz as center frequencies, respectively) are outlined. The measured radiation patterns show good symmetry and sidelobe suppression over 20-percent bandwidth inSandXbands and are in good agreement with calculated patterns.     

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