J. R. Mosig

Arbitrarily shaped microstrip structures and their analysis with a mixed potential integral equation

The author gives a comprehensive description of the mixed potential integral equation (MPIE) as applied to microstrip structures. This technique uses Greens functions associated with the scalar and vector potential which are calculated by using stratified media theory and are expressed as Sommerfeld integrals. Several methods of moments allowing the study of irregular shapes are described. It is shown that the MPIE includes previously published static and integral equations. Hence, it can be used at any frequency ranging from DC to higher-order resonances. Several practical examples including an L-shaped patch have been numerically analyzed and the results are found to be in good agreement with measurements. >

Analysis and design of terahertz antennas based on plasmonic resonant graphene sheets

Resonant graphene antennas used as true interfaces between terahertz (THz) space waves and a source/detector are presented. It is shown that in addition to the high miniaturization related to the plasmonic nature of the resonance, graphene-based THz antenna favorably compare with typical metal implementations in terms of return loss and radiation efficiency. Graphene antennas will contribute to the development of miniature, efficient, and potentially transparent all-graphene THz transceivers for emerging communication and sensing application.

On the network characterization of planar passive circuits using the method of moments

The issue of characterizing multiport planar circuits using the method of moments is addressed. For this purpose two commonly encountered excitation models, the delta-gap voltage, and the impressed-current ones are considered. The two excitation models are thoroughly examined and the conditions are determined under which they become equivalent. Based on this equivalence, it is shown how to correctly use the models for extracting the required network representation of general multiport planar circuits, possibly having transversely multisegmented ports, in an unambiguous way. Supportive numerical and experimental results for the characterization of shielded planar circuits are also provided.

Finite phased array of microstrip patch antennas: the infinite array approach

An efficient method of analysis of large infinite arrays based on a convolution technique that allows one to obtain the finite array characteristics from the infinite array results is presented. The edge effects are taken into account by convoluting the infinite array results with the proper current amplitude window on the array. The method is based on the use of Poissons sum formula in the case of finite arrays applied here to microstrip antennas. It is an approximate technique that can be assimilated into a perturbation method. >

Analysis of finite phase arrays of microstrip patches

A method for the analysis of large phased arrays of microstrip patches is presented. It is based on an infinite array approach where the edge effects are taken into account through the convolution with a proper window function. In the first step, a rigorous Greens function corresponding to a finite array of elementary sources is derived. This Greens function is then used to analyze the finite phased array of microstrip patches. Results are shown for the active impedance and element patterns of several arrays, and compared with measurements or, in the case of small arrays, with results obtained by a rigorous element-by-element approach. It is shown that the method, even if developed for the analysis of large arrays, is able to handle small arrays. Indeed, the results obtained are good even for single patches. Although the method has been developed for the microstrip phased array case, the results are general and are valid for any phased array with a rectangular grid. >

Analysis of stacked microstrip patches with a mixed potential integral equation

A method based on the mixed potential integral equation for the analysis of flat microstrip antennas in a double-layer substrate is presented. The method is used to compute the input impedance of a stacked patch configuration. This structure permits a larger bandwidth and may also provide dual-frequency operation. The Greens functions are discussed in detail, and numerical results are obtained for the propagation constant of the dominant surface wave. Theoretical and experimental results are compared for a dual-frequency and a broadband stacked patch antenna. Theoretical results for the input impedance are in good agreement with measurements. The difference between theoretical and experimental results for the resonant frequency is less than 4.5% in all cases. >

The Effect of Insulating Layers on the Performance of Implanted Antennas

This work presents the analysis of the influence of insulation on implanted antennas for biotelemetry applications in the Medical Device Radiocommunications Service band. Our goal is finding the insulation properties that facilitate power transmission, thus enhancing the communication between the implanted antenna and an external receiver. For this purpose, it has been found that a simplified model of human tissues based on spherical geometries excited by ideal sources (electric dipole, magnetic dipole and Huygens source) provides reasonable accuracy while remaining very tractable due to its analytical formulation. Our results show that a proper choice of the biocompatible internal insulation material can improve the radiation efficiency of the implanted antenna (up to six times for the investigated cases). External insulation facilitates the electromagnetic transition from the biological tissue to the outer free space, reducing the power absorbed by the human body. Summarizing, this work gives insights on the enhancement of power transmission, obtained with the use of both internal, biocompatible and external, flexible insulations. Therefore, it provides useful information for the design of implanted antennas.

Integral Equation Analysis of Plane Wave Scattering by Coplanar Graphene-Strip Gratings in the THz Range

The plane wave scattering and absorption by finite and infinite gratings of free-space standing infinitely long graphene strips are studied in the THz range. A novel numerical approach, based on graphene surface impedance, hyper-singular integral equations, and the Nystrom method, is proposed. This technique guarantees fast convergence and controlled accuracy of computations. Reflectance, transmittance, and absorbance are carefully studied as a function of graphene and grating parameters, revealing the presence of surface plasmon resonances. Specifically, larger graphene relaxation times increases the number of resonances in the THz range, leading to higher wave transmittance due to the reduced losses; on the other hand an increase of graphene chemical potential up-shifts the frequency of plasmon resonances. It is also shown that a relatively low number of graphene strips ( >10) are able to reproduce Rayleigh anomalies. These features make graphene strips good candidates for many applications, including tunable absorbers and frequency selective surfaces.

Two advanced solar antenna "SOLANT" designs for satellite and terrestrial communications

A novel hybrid technology where amorphous silicon (a-Si:H) solar cells are either integrated or physically combined with printed slot antennas is presented. This basic idea is demonstrated with the help of two innovative designs where the solar cells are directly grown on a stainless steel ground-plane or glued onto a standard copper layer printed on a dielectric substrate. To show the compatibility of solar cells and antennas, the concept is used to create a linearly polarized slot antenna, a circularly polarized slot antenna and a slot array. The concept offers advantages in terms of surface coverage, volume, weight and electric performance when compared with a simple juxtaposition of antennas and solar cells.

Evaluation of Weakly Singular Integrals Via Generalized Cartesian Product Rules Based on the Double Exponential Formula

Various weakly singular integrals over triangular and quadrangular domains, arising in the mixed potential integral equation formulations, are computed with the help of novel generalized Cartesian product rules. The proposed integration schemes utilize the so-called double exponential quadrature rule, originally developed for the integration of functions with singularities at the endpoints of the associated integration interval. The final formulas can easily be incorporated in the context of singularity subtraction, singularity cancellation and fully-numerical methods, often used for the evaluation of multidimensional singular integrals. The performed numerical experiments clearly reveal the superior overall performance of the proposed method over the existing numerical integration methods.