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     

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.<>     

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     

Broadband compact stacked T-shaped DRA with equilateral-triangle cross sections

A compact T-shaped dielectric resonator antenna (DRA) with two equilateral-triangle cross sections is investigated in this letter. The DRA is vertically placed on a finite ground plane and excited by a coaxial probe to provide broadband and conical radiation patterns. In order to examine the proposed design, simulations and measurements were employed to investigate the proposed antenna, and a good agreement between them was obtained. The proposed design produces an impedance bandwidth of more than 60% from 1.6 to 3.1GHz, which effectively covers several promising application bands in contemporary wireless communication systems, such as digital communication systems (DCS: 1710-1880MHz), personal communication systems (PCS: 1850-1990MHz), universal mobile telecommunication systems (UMTS: 1920-2170MHz), wireless local area networks (WLANs: 2.4-2.485GHz). Additionally, stable conical patterns were also obtained within the interest frequency band.     

同轴探针激励圆波导输入阻抗的研究

用等效电路的方法推导了圆波导内径向探针的输入阻抗表达式以及等效电路各参数的表达式，实验测量表明单个同轴探针与圆波导匹配良好。理论计算与实验测量吻合较好。     

Input impedance of an overmoded coaxial line fed coaxial waveguide

A theoretical formulation for the input impedance of an overmoded coaxial probe fed coaxial waveguide has been derived in terms of the geometrical variables, the modal field solutions, and the probe excitation current distribution. The formulation includes higher order mode propagation, a variable probe length, and general coaxial terminations in the secondary waveguide. The model compares well with experimental data derived from a structure supporting three propagating modes.     

Input Impedance of Coaxial Line to Circular Waveguide Feed

The expressions for the real, imaginary parts of the input impedance seen by a coaxial line driving a thin cylindrical probe in a dominant TE/sub 11/ mode circular waveguide are derived. The analysis is carried out by assuming that the cylindrical post is replaced by a curvilinear strip having maximum width equal to the diameter of the probe. Theoretical results on input VSWR and input impedance seen by a coaxial line are in close agreement with experimental data.     

Analysis of elliptical and circular microstrip antennas using moment method

A method of calculating the input impedance of either a circular or a slightly ellipitcal microstrip antenna excited by a coaxial probe is presented. Using the reaction integral equation and the exact dyadic Green's function, the finite substrate thickness is taken into account in the formulation. Good agreement with experimental results for an elliptical patch is obtained and a design procedure for a circularly polarized antenna is presented.     

Strip-fed rectangular dielectric resonator antennas with/without a parasitic patch

A rectangular dielectric resonator antenna (DRA) was studied theoretically and experimentally. The rectangular DRA is excited by a strip, which is compatible with a coaxial probe. Both linearly polarized (LP) and circularly polarized (CP) fields of the antenna are considered. In previous studies of the LP rectangular DRA, only the fundamental TE/sub 111/ mode has received much attention. In this paper, it is found that the fundamental TE/sub 111/ mode, together with the higher-order TE/sub 113/ mode, can be used to design a wide-band LP DRA. The bandwidth of the dual-mode DRA can be over 40% for a conventional rectangular DRA with a simple feed. For the CP mode, a parasitic patch is attached on a side wall of the DRA to excite a degenerate mode. In both the LP and CP cases, the finite-difference time-domain (FDTD) method is used to analyze the problems. The results agree reasonably with measurements.     

Analysis of an infinite phased array of dipole elements with RAMcoating on ground plane and covered with layered radome

An analysis of an infinite array of dipole elements over a radar absorbing material (RAM) coated ground plane and covered with a radome is presented. The radiation impedance of the dipole element is obtained when the array is in transmitting mode, and a scattering analysis is carried out when the array is excited by an incoming plane wave and the dipole elements are terminated in loads. The electric field Green's function in terms of Floquet mode expansion due to a periodic δ-function horizontal dipole source is derived to satisfy the layered boundary conditions. The method of moments is used to solve the current distribution on the dipole. Numerical calculation of the radiation impedance of a dipole array covered with a radome has been verified with results from waveguide simulator measurements. Numerical examples are given to show the effect of the RAM coated ground plane on the radiation impedance and the scattering characteristics     

Rigorous evaluation of the input impedance of a sleeve monopole bymodal-expansion method

A rigorous modal-expansion analysis is developed for obtaining the current distribution and input impedance of a sleeve-monopole antenna fed through an infinite ground plane by a coaxial line. A “perfectly matched boundary,” which is simply the combination of an electric wall and a magnetic wall, is initially proposed to facilitate the modal-expansion analysis. The walls are parallel to the ground plane at a variable height above it. Expansion coefficients of the electromagnetic fields are then determined by enforcing the boundary conditions at conducting surfaces and regional interfaces. Numerical results for the current distribution and input impedance of the sleeve monopole are presented and compared with available data in the literature. Very good agreement is observed. Also examined are the radiation pattern for different sleeve lengths and the effects of the length and finite thickness of the sleeve conductor on the antenna's input impedance     

Conformal strip excitation of dielectric resonator antenna

A new excitation scheme that employs a conducting conformal strip is proposed for dielectric resonator antenna (DRA) excitation. The new excitation scheme is successfully demonstrated by using a hemispherical DRA whose exact Green function is found using the mode-matching method. The moment method is used to solve the unknown strip current from which the input impedance is obtained. Novel recurrence formulas were obtained so that the impedance integrals are evaluated analytically. This solves the singularity problem of the Green function and substantially reduces the computation time. An experiment was carried out to verify the theory. The co- and cross-polarized field patterns are also shown. In addition, an experimental technique which deals with the problem of an air gap between the DRA and the ground plane is presented     

Rigorous Analysis of Rectangular Dielectric Resonator Antenna With a Finite Ground Plane

A probe-fed rectangular dielectric resonator antenna (RDRA) placed on a finite ground plane is numerically investigated using method of moments (MoM). The whole structure of the antenna is exactly modeled in our simulation. The feed probe, coaxial cable and ground plane are modeled as surface electric currents, while the dielectric resonator (DR) and the internal dielectric of coaxial cable is modeled as volume polarization currents. Each of the objects is treated as a set of combined field integral equations. The associated couplings are then formulated with sets of integral equations. The coupled integral equations are solved using MoM in spatial domain. The effects of ground plane size, air gap between dielectric resonator and ground plane, probe length, and position on the radiation performance of the antenna including resonant frequency, input impedance, radiation patterns, and bandwidth are investigated. The results obtained for the antenna parameters based on the MoM investigation shows that there is a close agreement with those obtained by measurement. Moreover it is shown that the MoM results are more accurate than other simulation results using software package such as High Frequency Structure Simulator (HFSS).      

On Solving TM0n Modal Excitation in a Ka-Band Overmoded Circular Waveguide by the Conservation of Complex Power Technique

To measure the radiation properties of relativistic diffraction generator (RDG) in Ka-band, a TM0n modal excitation model is established, which consists of an overmoded circular waveguide and a coaxial line feeding probe. Using the transverse E-field mode matching and the conservation of complex power technique (CCPT), we deduce the scattering matrix at coaxial line to coaxial line and coaxial line to circular waveguide junctions. Then using the overall cascaded junction scattering matrix, the numerical results for the reflection coefficient of the coaxial line and the power distribution of TM0n multi-modal are presented. The numerical results are in agreement with HFSS simulation results and experimental results. The analysis shows that by choosing the appropriate position of coaxial line probe, the power proportion of the device operating mode excited in circular waveguide could be the largest.     

On Solving TM0n Modal Excitation in a Ka-Band Overmoded Circular Waveguide by the Conservation of Complex Power Technique

To measure the radiation properties of relativistic diffraction generator (RDG) in Ka-band, a TM0n modal excitation model is established, which consists of an overmoded circular waveguide and a coaxial line feeding probe. Using the transverse E-field mode matching and the conservation of complex power technique (CCPT), we deduce the scattering matrix at coaxial line to coaxial line and coaxial line to circular waveguide junctions. Then using the overall cascaded junction scattering matrix, the numerical results for the reflection coefficient of the coaxial line and the power distribution of TM0n multi-modal are presented. The numerical results are in agreement with HFSS simulation results and experimental results. The analysis shows that by choosing the appropriate position of coaxial line probe, the power proportion of the device operating mode excited in circular waveguide could be the largest.     

An efficient numerical approach for modeling microstrip-typeantennas

An efficient numerical approach to model antennas that include a microstrip element radiating in the presence of material layers is developed. The class of antennas considered is fed through the ground plane by a coaxial transmission line. The reaction integral equation is formulated by treating the coaxial aperture as part of the antenna. The substrate thickness can be arbitrary, making this numerical technique suitable for high-frequency applications. The effects of the substrate are also included in the analysis. Numerical results are obtained for the current distribution and input impedance. The algorithm is validated with experimental results     

A Multifilament Method-of-Moments Solution for the Input Impedance of a Probe-Excited Semi-Infinite Waveguide

The input impedance and surface currents of a probe-excited, short-circuited semi-infinite waveguide are determined by the method of moments. Expressions are given for the impressed electric field used to excite the probe from the coaxial source input using a semi-infinite-waveguide Green's function, and expressions are given for a free-space approximate impressed electric field which arises from the coaxial source input. The method-of-moments formulation used is based on a multifilament current approximation and solves for the surface currents of the probe as a function of probe angle around the probe. Comparison of theory and experiment is made.     

Input impedance of microstrip patch in the quasi-optical cavity resonator

The dyadic Green's function in an active loaded quasi-optical oscillator is presented. An expression is derived for the input impedance of a single microstrip patch cavity excited by a coaxial probe using the method of moment. Using the present formulation the input impedance of a rectangular microstrip patch is determined.     

Higher order mode impedances and cut-off frequencies of overmoded coaxial waveguides

Using both theoretical and experimental methods the critical geometrical ratios for effective higher order mode superposition in coaxial waveguides are identified for SDMA beam forming antenna applications. Higher order mode impedances are also important in the design of such antennas and a closed form expression for the power-voltage definition of impedance is derived together with estimates for the voltage-current and power-current forms. An industry standard finite element solver is used to confirm the accuracy of these formulations for a 60?mm radius overmoded coaxial waveguide. In the second part of the paper, the mode chart is used to design a coaxially fed, overmoded air-spaced coaxial waveguide “T” junction supporting the TEM, TE ₁₁ and TE ₂₁ modes. A Green's function based model of the input impedance of this junction establishes that the power-voltage characteristic impedance occurs naturally in calculations requiring absolute impedance values. Finally, this input impedance model, which includes higher order and evanescent mode propagation, is demonstrated to agree well with experimental data for this junction.     

准光腔单微带贴片输入阻抗的理论分析

本文利用并矢格林函数获得了准光腔中的电磁场积分方程。利用矩量法导出了被一个轴向电流源激励的单微带贴片腔的输入阻抗的计算公式。利用本方法对矩形微带贴片的输入阻抗进行了讨论。其结果与微带天线很类似。这对设计微带型准光振荡器有重要的参考价值。