FDTD analysis of E-sectoral horn antennas for broad-bandapplications

The finite-difference time-domain (FDTD) method is applied to study the performance of E-plane sectoral horn antennas designed for broad-band applications. These antennas (proposed for 6-18 GHz phased arrays) have a large bandwidth, and they are easily array integrated. These antennas have a highly complicated geometry that is modeled using a polygonal approximation in the curved boundaries. Perfect matched layers (PMLs) combined with first-order absorbing boundaries are employed to simulate the free-space environment in the FDTD mesh     

FDTD analysis of electromagnetic wave radiation from systemscontaining horn antennas

The application of the finite-difference time-domain (FDTD) method to various radiating structures is considered. These structures include two- and three-dimensional waveguides, flared horns, a two-dimensional parabolic reflector, and a two-dimensional hyperthermia application. Numerical results for the horns, waveguides, and parabolic reflectors are compared with results from using the method of moments (MM). The results for the hyperthermia application are shown as extensions of the previously validated models. This new application of the FDTD method is shown to be useful when other numerical or analytic methods cannot be applied     

Near-field analysis of E-plane sectoral solid dielectric horn antennas

An approximate analysis of the aperture field of an E-plane sectoral solid dielectric horn antenna is described using the TE to x mode. The analysis is based on the solution of Maxwell's equations after making some simplifying assumptions. The electric and magnetic fields inside the horn core are matched to those outside at appropriate boundaries to yield transcendental equations which are then solved on a computer for the ropagation constants and field configurations. The theoretical results so obtained are in agreement with experimental results. Characteristic equations for the TM to x mode are also calculated and the results are compared with those of Marcatili, Goell, Eyges and Morita     

Radiation pattern of E-plane sectoral solid dielectric horn antennas

Radiation patterns of an E-plane sectoral solid dielectric horn excited by a rectangular metallic waveguide are predicted and compared with patterns measured at 9-37 GHz.     

Radiation patterns of metal and dielectric wall diagonal horn antennas

The radiation patterns and gain of dielectric wall diagonal horn antennas of various thicknesses (0.15cm and 0.32 cm) and dielectric constants (? = 2.54, 2.56 and 3.03) have been experimentally studied and compared with a metal diagonal horn antenna having the same aperture at 9.418 GHz. Radiation patterns of these dielectric horn antennas when used as square horns are also presented and compared with a similar metal horn. The use and applicability of dielectric horn antennas is discussed.     

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     

Numerical calculation of diffraction coefficients of genericconducting and dielectric wedges using FDTD

Classical theories such as the uniform geometrical theory of diffraction (UTD) utilize analytical expressions for diffraction coefficient for canonical problems such as the infinite perfectly conducting wedge. We present a numerical approach to this problem using the finite-difference time-domain (FDTD) method. We present results for the diffraction coefficient of the two-dimensional (2-D) infinite perfect electrical conductor (PEC) wedge, the 2-D infinite lossless dielectric wedge, and the 2-D infinite lossy dielectric wedge for incident TM and TE polarization and a 90° wedge angle. We compare our FDTD results in the far-field region for the infinite PEC wedge to the well-known analytical solutions obtained using the UTD. There is very good agreement between the FDTD and UTD results. The power of this approach using FDTD goes well beyond the simple problems dealt with in this paper. It can, in principle, be extended to calculate the diffraction coefficients for a variety of shape and material discontinuities, even in three dimensions     

Numerical modeling of a spherical array of monopoles using FDTD method

In this paper, the spherical-coordinate finite-difference time-domain method is applied to numerical analysis of phased array of monopoles distributed over a sphere. Outer boundary of the given problem is modeled by accurate spherical-coordinate anisotropic perfectly matched layer. The problem of increased cell aspect ratio near the sphere poles causing degradation of results is solved by dispersion optimization through artificial anisotropy. The accuracy of the approach is verified by comparing a model case with an exact solution. Finally, radiation patterns obtained by frequency-domain near-to-far-field transform and s-parameters of the array elements are presented and validated by comparing with measurement data.     

Numerical analysis of dielectric lens antennas using a ray-tracing method and HFSS software

In this paper, we use for the first time the ray-tracing method combined with the HFSS software to analyze lens antennas. HFSS is a very popular commercial tool that can provide very accurate results for the simulation of antennas. However, because of limitations on computational resources, it is hard to apply to solving large electromagnetic problems. In this paper, HFSS is used to simulate the fields of the feed part of a lens antenna. The ray tracing method is adopted for the lens part. This treatment makes the combined method feasible for solving large lens antennas. In using the ray-tracing method, cubicspline interpolation is exploited to fit the face of the lens and to solve for the derivatives at each point on the curved surface. Newton's method is applied to find the intercept between the ray and the curved surface. The numerical method proposed in this paper is very suitable for the analysis of dielectric lens antennas with arbitrary feeds and lens shapes. The validity of the idea is demonstrated by comparing the simulation results of this new method with those from using CST (Computer Simulation Technology) software. Very good agreement is achieved.     

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     

Analysis of pyramidal horn antennas using moment methods

A hybrid numerical technique is developed for electrically large pyramidal horn antennas radiating in free space. A stepped-waveguide method is used to analyze the interior surfaces of the horn transition. The electric field integral equation (EFIE) is employed on the outer surfaces of the pyramidal horn including the radiating aperture. Meanwhile, the magnetic field integral equation (MFIE) is used on the aperture to relate the aperture fields and those in the horn transition The resultant hybrid field integral equation (HFIE) is solved numerically by the method of moments. This formulation is both accurate and numerically stable so that high-gain microwave pyramidal horns can be analyzed rigorously. Far-field radiation patterns, both computed and measured, are presented for three electrically-large X-band horn antennas. The comparisons demonstrate that this method is accurate enough to predict the fine pattern structure at wide angles and in the back region. Computed far-field patterns and aperture field distributions of two smaller X-band horns are also presented along with a discussion on the validity of the approximate aperture field distributions routinely used in the analysis and design of pyramidal horns     

Modelling of dielectric losses in microstrip patch antennas: application of FDTD method

A frequency dependent complex permittivity is used to describe the dielectric losses of a microstrip patch antenna. The theoretical and experimental results for the usual parameters (input impedance, reflection coefficient and radiation pattern) of a rectangular microstrip patch are compared for a lossy and a nonlossy dielectric. Good agreement is obtained between the experimental measurements and theoretical results when the dielectric losses are considered.<>     

Numerical modeling of on-glass conformal automobile antennas

This paper presents the development of computer models for the analysis of on-glass conformal automobile antennas. The numerical models used are the method of moments (MoM) and the uniform geometric theory of diffraction (UTD). Models were developed to analyze antennas for low-frequency applications (AM), antennas on a resonant vehicle structure (FM), and high-frequency applications (cellular, Global Positioning System (GPS), radar). Calculation results were verified using measurements     

A conformal FDTD software package modeling antennas and microstrip circuit components

This paper describes a conformal finite-difference time-domain (CFDTD) software package, and presents its applications to RF antennas and microstrip circuit components. The program includes a Visual Basic GUI, for graphically inputting the object geometries, setting source and boundary conditions, generating a non-uniform mesh, and post-processing of the data. A robust CFDTD technique is employed to handle conductors with curved surfaces and edges. Illustrative examples that show the application of the code for modeling antennas as well as microstrip discontinuities are presented in the paper.     

A thin-rod approximation for the improved modeling of bare and insulated cylindrical antennas using the FDTD method

A general and consistent integral finite-difference time-domain (FDTD) formulation on cubical grids for modeling of cylindrical antennas with or without dielectric coating is derived. No additional grid points or modifications of the integral paths are necessary. Instead, effective material properties are modified in the FDTD grid. Thus, even for insulated antennas, the simple cubical structure is maintained. Special integral factors are defined on cubical elements, which take into account the behavior of fields in all directions in the neighborhood of the antenna. Applying these factors to the gap region and along the antenna's axis allows a correct modeling of the influence of the antenna's thickness. Furthermore, integral factors derived for the antenna's ends improve the modeling of the antenna's length. The accuracy of the method is confirmed by a systematic comparison with analytical and numerical results.     

Numerical modeling of dielectric-resonator antennas in a complexenvironment using the method of moments

Aperture coupled dielectric resonator antennas (DRAs) that reside above a layered background are analyzed using the method of moments (MoM). Dyadic Green's functions for the layered medium are derived in a simple and effective manner and the Rao-Wilton-Glisson (RWG) function is used to expand both electric and magnetic currents. A transmission-line technique is used to compute the antenna-input impedance. Numerical results obtained for both hemispheric and rectangular DRAB agree well with published measurement results     

Modelling of bow-tie microstrip antennas using modified locallyconformal FDTD method

An analysis of bow-tie microstrip antennas is presented based on the use of the modified locally conformal finite-difference time-domain (FDTD) method. This approach enables the number of cells along the antenna length and width to be chosen independently of the antenna central width, which helps to keep the number of cells required in those directions to a minimum. The analysis results are compared with experimental results and good agreement is observed     

Numerical analysis of dielectric resonator antennas excited in quasi-TE modes

A numerical analysis of a half-split cylindrical dielectric resonator (CDR) antenna on a conducting ground plane excited by a coaxial probe is presented. A procedure based on the method of moments (MoM) for the coupling of a body of revolution (BOR) to a non-BOR geometry is implemented. The antenna is operating in the TE/sub 01/ and HEM/sub 12/ modes. This antenna configuration has potential uses where high power handling capabilities and wide operating bandwidth are required.<>     

Phase centers of horn antennas using Gaussian beam mode analysis

The power of Gaussian beam mode analysis to accurately describe the propagation of electromagnetic beams and the location of a horn antenna phase-center is illustrated. By way of example, the case of a compensated pyramidal horn fitted with fins to produce a less abruptly tapered E-plane field distribution is discussed, and the results obtained are compared with those from an alternative method published in the literature. Excellent agreement is found     

Cavity losses modeling using lossless FDTD method

The impulse response of a lossless resonant system, usually obtained using the finite-difference time-domain method, permits us to determine the resonant frequencies through the Fourier transform. However, the obtained spectrum has no physical meaning since the losses have not been implemented. Rather than modeling physically the losses, we propose to apply a specific time-domain window to the already simulated signal of the lossless system. This Losses window depends on a user-defined quality factor. The advantage of this postsimulation losses implementation is a capability of parametric study of composite losses. Losses of various physical origins are found for example in the case of reverberation chambers.