Josip Seljan

A Full-Wave Hybrid Method for the Analysis of Multilayered SIW-Based Antennas

We propose a fast and accurate full-wave code capable of analyzing electrically large substrate integrated waveguides consisting of stacked parallel-plate waveguides hosting dielectric or metallic posts and coupling and/or radiating slots. Boundary conditions enforced on posts yield scattering amplitudes, while slots are modeled by equivalent magnetic currents, solved by a method of moments. Substantial accelerations are proposed to exploit various symmetries of the structures and to select the optimal number of modes according to the relevant geometrical and physical parameters. The formulation is validated by full-wave simulations with a commercial software and measurement results.

Efficient Computation of the Coupling Between a Vertical Line Source and a Slot

A novel spectral formulation is proposed here for the coupling integral between a cylindrical wave with arbitrary radial wavenumber and azimuthal dependence, and a slot placed on a plane orthogonal to the wavefront. Such a kind of integral is massively encountered in electromagnetic modeling of stratified structures comprising slots and vertical pins or vias. The twofold spatial integral defining the coupling is transformed into an equivalent onefold spectral integral, the integration path of which is selected to obtain Gaussian decay of the integrand. Both propagating and evanescent cylindrical modes are considered. An arbitrary stratification orthogonal to the slot plane can be considered, as well as an arbitrary current on the slot. Numerical comparisons against the standard spatial approach are shown to validate the new formulation, and its advantage in terms of computation cost is investigated in depth.

Efficient analysis of lossy substrate integrated waveguide structures

As frequency increases, conductor losses become an important loss mechanism in substrate-integrated-waveguide (SIW) based devices and may significantly degrade their performance. Therefore, one needs a general, reliable and efficient analysis tool that could properly take the aforementioned effect into account and consequently be used in design and optimization. In this presentation we propose a general analytical scheme for rigorous modeling of conductor losses in SIW devices within the recently proposed hybrid modematching/method of moments framework (M. Casaletti et al., IEEE-Trans. Antenna Propag., 11/2013; 5575-5588) for the fast and accurate analysis of multilayer SIW guiding/radiating structures. In particular, we extend the mode-matching part, originally accommodated to PEC boundaries, by generalizing it to boundaries describable in terms of Leontovich impedance boundary condition, which is able to incorporate the effects of both conductor losses and surface roughness. This mode-matching implementation can be subsequently incorporated in the general hybrid method. The description of lossy or rough metal surfaces as impedance surfaces allows the analytical derivation of the cylindrical wave vectors associated to the Parallel Plate Waveguide (PPW) hosting the SIW structure. This latter non-orthogonal complete basis set is used to represent, as a series expansion, the corresponding PPW Greens function and the field scattered by a general lossy/dielectric cylinder inside the PPW. The scattered field amplitudes are then obtained using an optimized mode-matching method. Special care is also needed for the derivation of the port parameters. Differences with the PEC case will be presented during the presentation. To validate our approach and demonstrating the necessity of incorporating the conductor losses in the modeling, several examples of lossy SIW devices will be considered, and the comparison with commercial software in terms of accuracy and resources will be presented.

Efficient computation of post-slot interactions in complex layered media with vertical interconnects

We present here the efficient computation of the integrals expressing the coupling between a cylindrical wave scattered by a vertical post in a layered structure and a slot etched on a metallic plane orthogonal to the post. This integral is required for the analysis of large layered structures with vertical interconnects. The twofold spatial integral is transformed into a single spectral integral. Its integration path is deformed in order to pass through the saddle point of the integrand, and obtain a Gaussian decay on the tail. A reduced number of quadrature points is required, and a significant speed up is achieved for complex structures composed of thousands of posts and slots.

A new synthesis technique for near-field focusing systems

Summary form only given. Pattern synthesis techniques have been widely used during the years to define and sculpt the radiation patterns of an antenna system in its far-field region. However, in several applications such as near-field probing and radiometry, medical imaging, etc. it is important to focus the energy in the Fresnel zone or even in the extreme near-field (reactive zone) of an electromagnetic device. In (J. W. Sherman, III, IRE Trans. Antennas Propagat., vol. AP-10, no. 4, pp. 399-408, July 1962), the properties of the electromagnetic fields in the far-field and Fresnel zone of a focusing radiating aperture are examined. The latter are the fields near the axis of a defined focal plane parallel to the aperture. It is shown that the fields in these two zones present the same properties as long as a quadratic phase taper of the tangential field distribution is adjusted on the focusing aperture. Therefore, the optimization/shaping of fields in the Fresnel zone can be achieved by using classical far-field techniques. However, this is not possible within the near-field or reactive zone of a radiating system. In contrast to previous works derived from Shermans conclusions, here we propose a new technique for shaping the near field of a focusing aperture based on an alternate projection method (O. M. Bucci, et al. Proc. IEEE, vol. 82, no. 3, pp. 358-371, Mar. 1994). The required near field is defined along a focusing plane in front of the aperture in terms of the desired axial pattern around the focal point and/or transverse plane patterns. The required field is described in terms of the focus depth, relative amplitude of forelobes and aftlobes. side lobe level, half power beamwidth, etc. Circular and linear polarized fields are considered. The possibility to control specific components of the field is also envisaged. Once the required near field pattern is defined, the aperture field distribution is found thanks to a combination of the alternate project method and a Fast Fourier Transform (FFT) algorithm. The FFT algorithm is used to evaluate the field at the focusing and aperture plane avoiding unnecessary approximations of previous works. Finally, a radial line slot array (RLSA) is used to synthetize the derived aperture field distribution in phase and amplitude. An in-house fast Method of Moments is employed during this step to control the aperture efficiency and distribution error. Several examples will be proposed during the conference. In particular, the possibility to generate with an RLSA arbitrary propagating Bessel beams will be presented. The proposed technique paves the way to the synthesis of any desired field shape in the near-field zone of a radiating structure.

Optimized analysis of slotted substrate integrated waveguides by a method-of-moments mode-matching hybrid approach

A full-wave hybrid formulation is proposed for the efficient and accurate modeling of substrate integrated waveguides by rigorously accounting for all possible interactions among elements such as vertical metallic or dielectric posts and coupling or radiating slots. The method is specifically accelerated in order to maximize the efficiency of the analysis of common structures. Its flexibility allows for the study of a large class of devices, possibly in stacked-waveguide configurations, and for the characterization of radiated fields and input port parameters.

Efficient analysis of SIW-based antenna geometries through a rigorous MoM mode-matching approach

An efficient full-wave code handling surface-integrated-waveguide based antennas is presented, implementing a hybrid method-of moments and mode-matching approach. Entire-domain basis functions are chosen to minimize the number of unknowns, and an efficient computation of Green functions for large radial distances is granted by means of a radial-transmission-line representation. The mode matching relies on an efficient cylindrical vector wave function expansion of the field. Both the accuracy and the efficiency are largely superior with respect to general-purpose commercial solvers.