Full wave analysis of the arbitrarily arranged spherical conformal microstrip antenna array

The dyadic Green's functions for a parallel-plate chirowaveguide are formulated by using the method of eigenfunction expansion. The eigenfunctions of the chirowaveguide are derived first in terms of two transformed fields. The purely solenoidal magnetic type dyadic Green's function is then expanded by these eigenfunctions. The electric type dyadic Green's function, which is solenoidal as well as longitudinal, is subsequently obtained from the magnetic dyadic Green's function through a simple relationship. It is found that the singular term in the electric dyadic Green's function accounting for the electric field in the source point is established through this latter procedure. The dyadic Green's functions obtained can be used to examine the electric and magnetic fields inside the chirowaveguide and to construct other dyadic Green's functions.

The dyadic Green's functions of the cylindrical chirowaveguide are derived by modal expansion. Bohren's decomposition of the electromagnetic field is used to obtain the vector wave functions. The magnetic dyadic Green's function that is purely solenoidal is first derived and the electric dyadic Green's function is then obtained by manipulating the magnetic dyadic Green's function. The singular term in the expression of the electric dyadic Green's function is reinstated through the manipulation procedure.

The classical problem of determining the complete spectral electric and magnetic Dyadic Green's Functions (DFG's) for 3D current sources imbedded within planar stratified background media is performed in a modern concise manner and notation. The expressions are then rearranged into "reference forms". This annotation is justified by examining the correspondence with the familiar free space expressions and clarifying some difficulties encountered in the formulation and numerical solution of Surface and Volume Integral Equations (S/V-IE's).

This paper presents a systematic and unified formulation of the dyadic Green's functions for multilayered biisotropic media. The media are stratified in a general direction which includes the canonical cases of planar, cylindrical and spherical geometries. Both electric and magnetic dyadic Green's functions are derived simultaneously based on the principle of scattering superposition. For the scattered dyadic Green's functions, their scattering coefficients are determined using the effective reflection and transmission concepts. This approach has avoided cumbersome operations and has also provided good physical insights to the scattering mechanism. The resulting general expressions are written in very compact and convenient forms. These expressions have been applied explicitly to the three canonical cases. For some common sets of biisotropic constitutive relations, their dyadic Green's functions are discussed and compared. The special case of multilayered isotropic media are considered as well.

The computation of electromagnetic fields in planar, multilayered, uniaxial media is discussed. In particular, a complete set of electric and magnetic dyadic Green functions (DGFs) is derived for such media in a computationally efficient and convenient to use form, based on a spectral domain transmission line equivalent network along the axis normal to the stratification. Efficient methods for the computation of the Sommerfeld integrals that arise in the DGFs are also presented.

The work presents a design of a cylindrical conformal phased microstrip antenna array. Based on the HFM and the parallel feed network, a conformal microstrip 2 times 8 array on a cylinder surface is designed by the isotropic transformation theory (IT). Simulation results show that the conformal array works at 35GHz and the gain is 19.6dB at the center frequency. The phase-scanned patterns of the conformal 2 times 8 array are analyzed by the CST using phase control method. From the comparison of the scanning results at different phase division, it can be found that the scan angle, the angular width and the side lobe level varies following the trends of the phase division, at the same time, the gain of the conformal array changes markedly opposite the trends of the phase division. Therefore, this is a shortcoming of the conformal phased array. This kind of conformal phased sub-array can be easily expanded into a large-scale conformal array and be suitable for active integration with other microwave circuits and communication systems if this disadvantage was eliminated after further discussion in future.

A novel equivalence principle algorithm (EPA) domain decomposition method previously for the surface integral equation is explored for volume integral equation in this work. The whole object is decomposed into several subdomains, the equivalence spheres are automatically produced to enclose each subdomain. The Rao–Wilton–Glisson (RWG) and body of revolution (BoR) basis functions are defined on the equivalence sphere surface. The equivalence currents defined on the RWG basis functions are evaluated with multilevel fast multipole algorithm, and then the currents defined on the RWGs can be projected onto the BoR basis functions. Compared with surface integral equation EPA-BoR algorithm, the ratio of the number of average original unknowns in each subdomain with respect to the equivalence unknowns is relatively larger, which leads to significant reduction of computations. Numerical simulations validate the accuracy and efficiency of the proposed method.

The objective of this paper is to present a formulation for the Inverse Scattering Problem [1] based on the expansion of the equivalent currents by using the Rao-Wilton-Glisson (RWG) basis functions [2]. The purpose is to reconstruct the sources from measured near-field data. The goal is to improve the resolution for the equivalent sources characterization, by avoiding the currents discontinuity along the edges when using pulse basis function. Moreover, in order to improve the accuracy of the reconstructed currents, the resulting matrix system has been solved by using the singular value decomposition (SVD) method. A comparison between the formulation with the pulse basis functions and the RWG basis for the inverse problem is presented.

The space mapping (SM) technique is applied to conformal antenna design for the first time. A planar microstrip antenna printed on a finite ground-plane with a coarse-mesh is solved as the coarse model and aligned with a conformal microstrip antenna placed on a platform's surface with a fine-mesh through space mapping. When some conformal antennas have the same planar configuration, being able to share a common coarse model is an important advantage of this technique in these conformal antenna optimizations. The S-parameters of conformal antennas are optimized. The function responses in this example are chosen as "e S11". The comparisons of efficiency and accuracy with the commercial software CST MWS 5.0 are made. The final results demonstrate that the SM technique can reduce the overall design process by an order of magnitude (10 times). Therefore, the proposed technique is particularly suitable for conformal antenna optimization. As a demonstration, examples of a planar broadband E-shape microstrip antenna placed on two different platform' surfaces are introduced in this communication.

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.

The ultimate goal of this work is to obtain accuracy for the MFIE that is just as good as the EFIE for Rao-Wilton-Glisson (RWG) basis functions. It is hoped that regularization will provide similar benefits for RWG as for pulse functions, since RWG basis functions have a pulse type dependence (abrupt edge) on two sides of each triangular mesh element.

An electric field integral equation (EFIE) formulation using the loop-star basis functions has been developed for modeling plane wave scattering from perfect conducting objects. A stability analysis at the DC limit shows that the use of the Rao-Wilton-Glisson (RWG) basis functions results in a singular matrix operator. However, the use of the loop-star basis functions results in a well-conditioned matrix. Moreover, a preconditioner constructed from a two-step process, based on near interactions and an incomplete factorization with a heuristic drop strategy, has been proposed in conjunction with the conjugate gradient method to solve the resulting matrix equation. The approach is shown to be effective for resolving both the low frequency instability and the bad conditioning of the EFIE method. The computational complexity of the proposed approach is shown to be O(N/sup 2/).

A conformal microstrip antenna is highly integrated with the carrier profile, giving it the advantage of reduced carrier space. However, the processing technology for fabricating an antenna with a conformal surface is complicated and expensive owing to its irregular shape. Therefore, it is particularly important to find ways to reduce the difficulty in producing conformal conductive patterns. For the production of conformal microstrip antennas, a five-axes motion printing system is proposed to print conductive patterns on nonexpanded surfaces. The conductive pattern uses a new boundary-alignment-optimization algorithm in the printing process to improve the accuracy of the boundary of the conductive pattern by optimizing the ink-dropping points in the motion command. The short-time and low-temperature sintering of the conductive pattern by using a flash light enables it to exhibit conductive properties. This method is practically implemented to fabricate a conformal array microstrip antenna. The main and side lobes of the electric and magnetic fields in the directional pattern measured in the microwave darkroom have the same trend as in the simulation diagram. Thus, the effectiveness of this method was verified through simulation analysis and experimental results.

FEKO is a 3D simulation tool for the analysis of electromagnetic fields. The simulation using FEKO is based on the well-known method of moments (MoM) for the Maxwell equations. FEKO can solve the problem of any structural type with a very comprehensive MoM code or tailored code. First, a radiation pattern for conformal microstrip antenna on the surface of cylinder is calculated using FEKO. In addition, the impact of conformal carrier on the radiations of microstrip antennas in different positions is simulated by FEKO. The simulation results accord with the true characteristics of conformal microstrip antennas.

An efficient closed-form asymptotic representation for the Dyadic Green's function for the grounded double-layered anisotropic uniaxial geometry is developed. In the present asymptotic development the large parameter is directly proportional to the lateral separation between the source and observation point. The asymptotic solution developed remains accurate even for very small lateral separation of the source and field points. The asymptotic closed-form Dyadic Green's function has been cast in such a form that the physical behavior of the electromagnetic fields due to anisotropy of the medium reveals itself through simple mathematical parameters. Thus, the physical understanding of the interaction of the spatially confined source with a grounded anisotropic (uniaxial) double-layered material slab is greatly enhanced through the new representation. Also, this representation is very useful in the moment method solution of the current excited on the microstrip antennas and arrays in a grounded double-layered uniaxial geometry, as well as the volumetric current excited within a dielectric scatterer buried in a ground double-layered anisotropic uniaxial slab. >