Improvement in efficiency-bandwidth product in small dielectricloaded antennas

The efficiency-bandwidth product (EB) is used in the evaluation of small dielectric loaded monopole antennas (DLMAs). The EBs of the DLMAs have been precisely measured on the basis of the Wheeler cap method. As a result, an improvement in the EB of electrically small cylindrical DLMAs has been confirmed experimentally in comparison with that in a bare monopole antenna. In addition, within the category of electrically small antennas considered here, it seems that there exists an optimum value of permittivity for the dielectric loading for which the best EB value is obtained     

Eigenmode analysis of dielectric loaded top-hat monopole antennas

Eigenmode expansions are used for computing the currents on a dielectric loaded top-hat monopole radiating above an infinite conducting ground plane. The approach is facilitated by adding a parallel ground plane above the antenna, thus allowing use of cylindrical harmonic field expansions in each of three regions. Expansion coefficients are found by enforcing boundary and continuity conditions at conducting surfaces and regional interfaces. Convergence and accuracy are assessed using comparisons with three other methodologies, namely an integral equation solution, a quasi-static analysis, and multi-octave experimental measurements     

Gain enhancement of dielectric resonator loaded waveguide antennas with dielectric overlays

The gain characteristics of a dielectric resonator loaded coaxial fed circular waveguide antenna (DRLWA) with overlaying parasitic discs have been investigated experimentally. Results indicate that, when properly spaced, the overlays can enhance the gain by more than 6 dB.<>     

Mode-matching analysis of top-hat monopole antennas loaded withradially layered dielectric

A top-hat monopole antenna with homogeneous or inhomogeneous dielectric loading over a ground plane is considered. Mode-matching analysis with proper enforcement of edge conditions is applied to the problem. The results of this technique are verified through independent calculations of admittance as well as by comparison of fields across matching regions. Measurements were also taken for comparison with the results from the model. It is shown that dielectric loading can reduce the electrical size necessary for self resonance, but only at the expense of a large increase in radiation Q     

Radiation characteristics of strip loaded hollow dielectric E-planesectoral horn antennas

The authors report the development of a novel E-plane sectoral horn. A metallic strip of optimum length loaded on the horn is capable of giving symmetric patterns both in the E and H-planes with low sidelobe levels     

Input impedance analysis of dielectric covered/loaded biconical antennas using mode-matching theory

The influence of the dielectric material on the input impedance of covered/loaded biconical antennas is analytically investigated. Novel and accurate analytical expressions for the input impedance of the covered/loaded bicon are proposed based on the mode matching technique. The boundary conditions are also enforced to obtain several simultaneous equations for the discrete modal coefficients inside the radiating region. Study of the input impedance of the whole multilayered structure is accomplished by the cascade connection of mediums as characterized by their constitutive parameters. New and accurate analytical formulas for the covered/loaded biconical antennas are derived and successfully validated through a proper comparison with the results obtained with the commercial software CST Microwave Studio.     

Planar antennas on a dielectric surface

A theory has been developed for planar metal antennas on a dielectric surface and the main predictions have been verified experimentally. Current dipole antennas have radiation diagrams and impedances favourable for microwave to far-infra-red integrated circuits.     

Endfire tapered slot antennas on dielectric substrates

Endfire tapered slot antennas are suitable for many integrated circuit applications, imaging and phased arrays. We report on an investigation of single elements of such antennas, including slots which are exponentially tapered (Vivaldi), linearly tapered (LTSA) and constant width (CWSA). For antennas of all types, a good general agreement is obtained for curves of beamwidth versus length, normalized to wavelength, when one compares the data with that for traveling-wave antennas published by Zucker. An important condition for this agreement is that the effective dielectric thickness, defined in the text, is in a certain optimum range. This condition is qualitatively explained in terms of the theory for traveling-wave antennas.     

CPW-fed slot antennas on multilayer dielectric substrates

Coplanar wave (CPW)-fed slot antennas printed on multilayer dielectric substrates are numerically analyzed using a full-wave integral equation technique and the method of moments. The Green's function is derived with an iterative formulation. Results obtained with a simplified and a rigorous model of the feeding CPW lines are compared. The mutual coupling between the slot antennas in an array environment is calculated for a three-layer high-low-high permittivity combination. The theoretical results are verified with measurements     

Parasitic array of two loaded short antennas

A double impedance loading technique is applied in the study of a parasitic array of two loaded short antennas, Approximate solutions for the currents in the array elements are obtained. It is demonstrated that the current distributions in the array elements can be appropriately modified by optimum impedance loadings to achieve significant improvement in radiated power or directivity. Theoretical predictions are verified closely by the results of an experimental study.     

Radiation characteristics of dielectric tube antennas

A study of the radiation characteristics of dielectric tube antennas is made with a possibility of its application in communications satellites. It has been shown through a systematic analysis that a multimoded dielectric tube shows a dip in the boresight region which is suitable for satellite antennas.     

Patch antennas on externally perforated high dielectric constantsubstrates

Smaller physical size and wider bandwidth are two antenna engineering goals of great interest in the wireless world. To this end, the concept of external substrate perforation is applied to patch antennas in this paper. The goal was to overcome the undesirable features of thick and high dielectric constant substrates for patch antennas without sacrificing any of the desired features, namely, small element size and bandwidth. The idea is to use substrate perforation exterior to the patch to lower the effective dielectric constant of the substrate surrounding the patch. This change in the effective dielectric constant has been observed to help mitigate the unwanted interference pattern of edge diffraction/scattering and leaky waves. The numerical data presented in this paper were generated using the finite-difference time-domain (FDTD) technique. Using this numerical method, a patch antenna was simulated on finite-sized ground planes of two different substrate thicknesses, with and without external substrate perforation. The computations showed the directivity drop in the radiation pattern caused by substrate propagation was noticeably improved by introducing the substrate perforation external to the patch for the case of a patch antenna on a relatively thick substrate without any loss of bandwidth. Measurements of a few patch antennas fabricated on high dielectric constant substrates with and without substrate perforation are included for completeness. Good correlation between the computed results and measurements is observed     

Design of electrically loaded wire antennas using geneticalgorithms

A novel antenna design procedure based on genetic algorithm (GA) driven optimization is proposed and applied to the synthesis of wire antennas loaded with lumped components. Loading circuit parameters, locations of the loads along the antenna, as well as matching network parameters, are optimized simultaneously. A computational scheme based on the Sherman-Morrison-Woodbury formula for the fast evaluation of the antenna performance for many distinct loading configurations is developed. The GA iteratively guides a population of randomly selected design candidates toward the optimal solution. The success of the proposed procedure is demonstrated through its application to the design of efficient ultra-broadband antennas and their corresponding matching networks     

Input impedance of aperture-coupled dielectric resonator antennas

Dielectric resonator antennas (DRAs) excited by a narrow-slot aperture in a conducting ground plane are analyzed using a numerical technique based upon a surface-integral equation formulation for bodies of revolution (BORs) coupled to non-BOR geometries. An efficient matrix-solution algorithm, together with a simple microstrip transmission-line model or a delta-source model are used to compute the antenna input impedance. Input impedances obtained with this technique show favorable agreement to those obtained via another numerical technique, as well as to those obtained by measurement     

High-frequency analysis of integrated dielectric lens antennas

A high-frequency method for the three-dimensional analysis of integrated dielectric lens antennas is presented. This method consists on improving the physical optics (PO) currents on the lens surface by modifying, via suitable transition functions, the spreading factor of those rays from the source point which arrive at the lens-air interface close to the critical angle of incidence. Invoking the locality principle of the high-frequency phenomena, the method uses the rigorous canonical solution of the semi-infinite dielectric space locally tangent at the lens surface. A uniform asymptotic evaluation of this canonical solution is provided with the introduction of a new transition function for the TM case. The present formulation provides significant correction from the PO currents of an elliptical lens, with a consequent improvement of the radiation pattern prediction, testified by comparisons with results from a full-wave analysis.     

Performance degradation of dielectric radome covered antennas

Performance is evaluated by a method based on the reciprocity theorem. The asymptotic expression for the radome Green's function that allows the characterization of the radome by itself, independently of any specific antenna, is identified. The concept of the modified aperture distribution, which radiating in free space produces the same pattern as the radome-covered antenna, is introduced. It can be used for the design of the radome stratification and for the optimization of the antenna location. On the basis of the formulation of a computer code has been developed that analyzes the degradation induced by radomes with surfaces and dielectric stratifications that can be defined numerically. Theoretical predictions and experimental results are compared     

Coplanar waveguide excitation of dielectric resonator antennas

The circuit and radiation properties of a cylindrical dielectric resonator antenna excited by a coplanar waveguide feed are investigated. The coupling between the feed and the radiator was measured as a function of the position, dielectric constant, and height of the cylinder. The radiation patterns and resonant frequencies were also measured. These measured results are found to be in good agreement with theoretical calculations     

Array of circular-polarised cross dielectric resonator antennas

A compact array of circular polarised cross-shaped dielectric resonator antennas (XDRAs) is presented. The array consists of 2×2 XDRAs elicited by microstrip-fed slot apertures in the X-band. By using sequential rotation to feed the XDRAs, the circular polarisation bandwidth is significantly increased from 5% for the individual XDRA to 16% in the array. The array also achieves a wide impedance bandwidth: a 10 dB return loss was maintained over a 25% bandwidth     

Triangular ray-tube analysis of dielectric lens antennas

A new method of analysis for the radiation characteristics of dielectric lens antennas with arbitrary inner and outer surfaces is presented. The analysis is based on representing the feed illumination by a contiguous set of ray tubes and including the effects of surface reflections and ray divergence. Radiation patterns and the antenna gain are then computed by evaluating the closed-form expressions developed for the Kirchhoff's integral of the aperture fields. The validity of the analysis method has been demonstrated by comparing the computations with measured results of two different spherical lenses and a shaped lens configurations. The analysis method presented takes into account some of the practical aspects associated with lens design such as surface zoning to reduce the mass and surface matching to minimize the reflection loss     

Mutual impedance of hemispherical dielectric resonator antennas

The mutual coupling between two hemispherical dielectric resonator antennas is studied analytically. The radiation fields of the antennas are derived rigorously from a Green's function. The mutual impedance is then determined from a reaction formula. Comparison between theory and experiment is presented