Performance analysis of spherical patch arrays

A hybrid technique of the finite-element method and the method of moments (FEM/ MoM) is used to analyze the effects of multilayered superstrates on cavity-backed slot (CBS) antennas. The spectral-domain approach is used to compute the MoM admittance matrix. An asymptotic extraction technique is applied to improve the computational efficiency of the convolution integrals. Effects on the input impedance, efficiency, gain, and radiation patterns are presented for different antennas. The numerical results are validated with measurements and published data.

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 TE/sub 111/-mode characteristic equation of the DRA is also studied, from which the simple formulas for the resonant frequency and Q-factor are obtained.

Array scanning method (ASM) is employed to study the input impedance and radiation pattern of a two-dimensional periodic leaky-wave antenna (LWA). The antenna consists of a narrow horizontal strip dipole of arbitrary length underneath a two-dimensional (2D) periodic screen of metallic patches, which acts as a partially reflective surface (PRS), and backed by a ground plane. First, the Green's function in the presence of the 2D array of metallic patches is calculated by means of the ASM and then the current distribution and input impedance of the source dipole are calculated through the electric field integral equation and method of moments. The far-field pattern is computed using the reciprocity theorem. Compared to the Hertzian dipole, which is the only type of source that has been considered in the literature, the resonant dipole substantially improves the performance of periodic LWA in terms of radiated power, efficiency and bandwidth. Numerical results are given for a resonant dipole over the frequency range of 60-70 GHz and compared with those obtained from commercial softwares, FEKO ® and Ansys HFSS ® , showing an excellent agreement with considerable improvement in terms of memory usage and computational speed.

In this article, a fast and efficient hybrid method that combines the volume-surface integral equation (VSIE) and the modified surface integration (MSI) method is proposed to evaluate the electromagnetic (EM) performance of the large-/medium-sized radome-enclosed antennas (REAs). An approximate equivalence principle is presented to formulate the physical model for the EM radiation of the REA, and then, the full-wave VSIE for the antennas and the high-frequency MSI method for the dielectric radome are coupled with each other in an iterative manner. Since mutual interactions up to the second order among the antennas and the radome are considered, the method shows good accuracy in both the near- and far-field regions of the REA system. In addition, all the computation processes involved in the method, including the method of moments (MoM) solution of the VSIE, surface integrations (SIs) in the MSI, and ray tracing for determining the local transmission matrix for the dielectric radome, are accelerated by the multilevel fast multipole algorithm (MLFMA), which makes the method highly efficient in terms of both computational time and memory requirement. Numerical results show that the proposed hybrid method can predict the EM performance, e.g., the input impedance and radiation pattern, of the REA system with good accuracy compared with the full-wave simulations.

The hemispherical dielectric resonator antenna (DRA) excited by a single-arm spiral slot is studied theoretically in this paper.The Green's function technique is employed to formulate an integral equation for the spiral slot current.The moment method with piecewise sinusoidal (PWS) basis and testing functions is used to convert the integral equation into a matrix equation by using a deltagap exciting source.The input impedance, return loss, axial ratio and radiation pattern are calculated.Numerical results demonstrate that the analysis is efficient.

The ability of the finite-difference-time-domain (FDTD) method to calculate radiation patterns, input impedance, and gain for a monopole antenna on a conducting box is demonstrated. Results are given for the bare box and with the box coated with a dielectric layer. Radiation patterns are compared with measurements and with the method of moments for the bare box. Radiation patterns for the dielectric-covered box and all impedance and gain results are compared with measurements only. Good agreement is obtained in all cases. The FDTD approach includes a dielectric covering quite easily, while this would be quite difficult for a method of moments approach. The FDTD method requires similar computer time as the method of moments for a single-frequency result, but produces wide-bandwidth impedance and gain results with much less computer time. >

The authors proposed a circularly polarized conical beam spherical slot array antenna for applications of low bit rate or low gain/temperature ratio (G/T) land mobile satellite communication and broadcasting services in addition to wireless local area network base stations (see Krairiksh, M. et al., Int. J. Electronics, vol.86, no.7, p.815-23, 1999). The advantage of this antenna is that the structure is simple and suitable for mass production and the feeding structure is also simple. From preliminary results, the radiation pattern appears to be a conical beam (see Phongcharoenpanich, C. et al., IEICE Trans. Electronics, vol.E82-C, no.7, p.1242-7, 1999). This paper presents the theory and experiment of a circularly polarized conical beam spherical slot array antenna. The theoretical result is carried out by means of the method of moments. With the aid of the dyadic Green's function, the integral equations of the unknown currents are solved by using entire domain basis functions and Galerkin's method. The theoretical results of the radiation pattern, elevation angle and directivity, input impedance and axial ratio are illustrated. The experimental results agreed satisfactorily with the theoretical ones.

This paper first examines and corrects Storer’s theory of circular loop antennas, and then investigates theoretically the proposed Ω-shaped loop-dipole antenna. Special emphasis is given to the analysis of the effect of the higher-order terms of the Fourier series as a remainder on the current distribution, input impedance, and radiation patterns of the thin-wire circular loop antenna. It is found that the remainder must be included in the calculation of the current distribution and input impedance but can be neglected to simplify the calculation of far-field radiation. Then, a theoretical model is proposed to analyze the radiation fields, directivity, and input impedance of the proposed Ω-shaped loop-dipole antenna based on the loop and dipole antennas’ theories. Analytical expressions for the radiation fields, directivity, and input impedance of the Ω-shaped loop-dipole antenna are derived. The theoretical and numerical results are compared for the Ω-shaped loop-dipole antennas of practical interests. They are in good agreement.

An eigensolution expansion of dyadic Green's function for cylindrical sector structures is presented. The cylindrical structure is limited in azimuthal direction by electric or magnetic walls. Due to orthogonality of the eigensolution functions between the walls, the derivation of the dyadic Green's function can be done in spectral domain. The Green's dyad is used to set up an electric field integral equation for the microstrip structure. The solution is carried out with the method of moments. Numerical results for input impedance and radiation pattern are shown.

The input and mutual impedances of rectangular microstrip patches mounted on a spherical structure are studied in the paper. The analysis approach is based on the moment method where the elements of the moment method matrix are calculated in the spectral domain. In order to avoid numerical problems a modified vector-Legendre transformation and normalized Legendre polynomials are defined and applied to the solution procedure. An approximate method is developed to calculate coupling between basis and test functions located on different patches. A laboratory model is built to test different configurations of patches and to validate the calculated results.

The long-standing problem of constructing an accurate equivalent circuit for receiving antennas by handling both the absorbed and scattered powers for all kinds of antennas, is addressed. By combining the electrical properties of the antenna with its radiating and scattering characteristics, it is shown that the input impedance, radiation pattern and vectorial effective height are three essential parameters to which the open-circuit scattering parameter (new) should be added. The antenna's power budget is then established and applied to various kinds of antennas. Theoretical results showed a perfect agreement with the method of moment (MoM) and the finite integration technique (FIT) over a large frequency-range under various conjugate-matched loads. It comes out that good radiating antennas are good scatterers as well but, without a precise power budget calculation, it is not evident to predict whether an antenna would absorb more or less than it scatters. Thin-metallic structure directive antennas (TMSDA) appear to be the best candidates to absorb more than they scatter under matching conditions. The two-element Yagi antenna can reach an absorption efficiency of 65%, while the pyramidal horn achieves only 12% maximum. The dipole is confirmed at 50%-absorption efficiency.

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).

A rectangular cavity backed slot antenna with two parallel parasitic slots is proposed to widen the bandwidth. The method of moments (MoM) is used to calculate the input impedance, VSWR, and radiation pattern where the effect of the cavity is taken into account. The VSWR bandwidth (/spl les/ 2) is increased from 4.6 % to 10.6 % by introducing two parasitic slots.

Purpose – The paper aims to propose an artificial neural network (ANN) in conjunction with spectral domain formulation for fast and accurate determination of the resonant frequency and quality factor of circular microstrip antenna printed on isotropic or anisotropic substrate. This neurospectral approach reduces the problem complexity. Design/methodology/approach – The moment method implemented in the spectral domain provides good accuracy but its computational cost is high due to the evaluation of the slowly decaying integrals and the iterative nature of the solution process. The paper introduces the electromagnetic knowledge combined with ANN in the analysis of circular microstrip antenna on isotropic or uniaxially anisotropic substrate to reduce the complexity of the spectral approach and to minimize the CPU time necessary to obtain the numerical results. Findings – The resonant frequency results obtained from the neural model are in very good agreement with the experimental and theoretical results available in the literature. Finally, numerical results for the substrate anisotropy effect on the resonant frequency, quality factor and radiation pattern are also presented. Originality/value – The paper develops fast and accurate model based on ANN technique to calculate the resonant frequencies and quality factors of circular microstrip antennas. ANN is used to model the relationship between the parameters of the microstrip antenna and the resonant frequencies and quality factors obtained from the spectral domain approach. This relatively simple model allows designers to predict accurately the resonant frequencies and quality factors for a given design without having to develop or run the spectral method codes themselves. The main advantages of the method are: less computing time than the spectral model, results with accuracy equivalent to that of full-wave models and cost effectiveness, since the client can use a simple PC for implementation. Another advantage of the proposed ANN model is that it takes into account the uniaxial anisotropy in the substrate without increasing the network size. This is done by combining ANN with electromagnetic knowledge.

A hybrid method using Method of Moment (MoM) and Transmission Matrix (TM) is first time applied in the analysis of log-periodic dipole array antennas (LPDA) in this paper. It utilizes the advantages of both MoM and TM. And this method doesn't need to construct an extended matrix which usually has to be used in other methods. Further more, it has very clear physical meaning. In order to solve the Pocklington's integral equation, an iteration technique is adopted. The effectiveness is demonstrated by calculation the radiation pattern, input impedance, current and voltage distribution of LPDA. The results using this method agree very well with the results of other references.