Maria Garcia-Vigueras

1D-Leaky Wave Antenna Employing Parallel-Plate Waveguide Loaded With PRS and HIS

A new type of one-dimensional leaky-wave antenna (LWA) with independent control of the beam-pointing angle and beamwidth is presented. The antenna is based on a simple structure composed of a bulk parallel-plate waveguide (PPW) loaded with two printed circuit boards (PCBs), each one consisting of an array of printed dipoles. One PCB acts as a partially reflective surface (PRS), and the other grounded PCB behaves as a high impedance surface (HIS). It is shown that an independent control of the leaky-mode phase and leakage rate can be achieved by changing the lengths of the PRS and HIS dipoles, thus resulting in a flexible adjustment of the LWA pointing direction and directivity. The leaky-mode dispersion curves are obtained with a simple Transverse Equivalent Network (TEN), and they are validated with three-dimensional full-wave simulations. Experimental results on fabricated prototypes operating at 15 GHz are reported, demonstrating the versatile and independent control of the LWA performance by changing the PRS and HIS parameters.

Quasi-Analytical Modeling of Transmission/Reflection in Strip/Slit Gratings Loaded With Dielectric Slabs

This paper presents a quasi-analytical approach to study the classic topic of transmission/reflection of electromagnetic waves through 1-D periodic arrays of strips/slits in metal screens. The approach is based on standard waveguide discontinuity theory. Starting from field equations, it is inferred a circuit-like reduced-order model with just one parameter to be determined. The value of this parameter can be obtained from the transmission/reflection coefficient provided by any full-wave method at just one single frequency. In this way, the computation effort to obtain very wide-band responses of periodically distributed slits or strips under oblique TE/TM illumination in the presence of loading dielectric slabs is reduced to the full-wave analysis of the structure at a single frequency value. For relatively narrow strip/slit gratings, this procedure gives very accurate results even for very complicated transmission/reflection spectra. An additional advantage of the present approach is that it allows for an easy understanding of the underlying physics of the phenomena involved.

A Modified Pole-Zero Technique for the Synthesis of Waveguide Leaky-Wave Antennas Loaded With Dipole-Based FSS

An extension of the pole-zero matching method proposed by Stefano Maci for the analysis of electromagnetic bandgap (EBG) structures composed by lossless dipole-based frequency selective surfaces (FSS) printed on stratified dielectric media, is presented in this paper. With this novel expansion, the dipoles length appears as a variable in the analytical dispersion equation. Thus, modal dispersion curves as a function of the dipoles length can be easily obtained with the only restriction of single Floquet mode propagation. These geometry-dispersion curves are essential for the efficient analysis and design of practical EBG structures, such as waveguides loaded with artificial magnetic conductors (AMC) for miniaturization, or leaky-wave antennas (LWA) using partially reflective surfaces (PRS). These two practical examples are examined in this paper. Results are compared with full-wave 2D and 3D simulations showing excellent agreement, thus validating the proposed technique and illustrating its utility for practical designs.

Simplified Circuit Model for Arrays of Metallic Dipoles Sandwiched Between Dielectric Slabs Under Arbitrary Incidence

This work presents an equivalent circuit to model the transmission/reflection of a plane wave that impinges obliquely on a periodic arrangement of metallic rectangular dipoles embedded between two dielectric slabs. The equivalent circuit takes advantage of the periodicity of the structure to reformulate the original problem as a certain equivalent waveguide scattering problem. Equivalent transmission lines are used to simulate the wave propagation whereas equivalent lumped circuit elements account for presence of the metallic patches. The obtaining of the circuit parameters is carried out via a systematic procedure, which provides a robust strategy that gives rise to surprisingly accurate results even for rather complex situations. The proposed equivalent circuit model simplifies considerably the original complex electromagnetic problem and provides a valuable physical insight into the parameters that are relevant in the phenomenon as well as an in-depth understanding of the operation principles of the periodic surface. Thus, the reported reduced-order model of the corresponding scattering problem can be a very convenient and helpful tool for the analysis and/or design of many practical devices.

Enhancing Frequency-Scanning Response of Leaky-Wave Antennas Using High-Impedance Surfaces

The use of high-impedance surfaces (HISs) to increase the frequency-scanning sensitivity of hollow leaky-wave antennas (LWAs) is presented. The LWA consists of a hollow rectangular waveguide with one of its narrow walls replaced by a partially reflective surface, and it is loaded with a metallodielectric HIS to increase its beam-scanning response. Theoretical results based on a simple transverse equivalent network illustrate the physical mechanism responsible for the improvement, and they are verified by experiments on a prototype working in the 11-16 GHz band.

Simplified Modal Expansion to Analyze Frequency-Selective Surfaces: An Equivalent Circuit Approach

This communication extends a previously reported analytical circuit that models the plane wave scattering by 2-D arrays of planar patches/apertures embedded in a layered media. In this extension, it is assumed that the current/electric field spatial profile in the patch/aperture region can directly be taken from the eigenfields of a waveguide whose cross section matches the scatterer boundaries. This methodology exploits all the advantages of the circuit modeling and gives place to a very efficient computational tool for many practical frequency-selective surfaces (FSSs). The circuit model is expected to work up to frequencies where the isolated scatterers have their third resonance. Thus, it allows us to provide unified equivalent circuits to deal with conical incidence and with certain symmetric cases involving two or three patches/apertures in the unit cell.

Circuit-Model Analysis of Frequency Selective Surfaces With Scatterers of Arbitrary Geometry

An equivalent-network model is here proposed to characterize two-dimensional planar periodic arrays of arbitrary scatterers/apertures embedded in a layered environment. The model is an extension of the approach previously developed by some of the authors, which only considered simple rectangular scatterers. A key underlying assumption in the present approach is that the current/field distribution in the scatterer can be factorized so that the spatial profile is independent of the frequency in the considered range of interest. This approximation is proven to work properly for a great variety of useful planar scatterer/aperture patterns, even at frequencies within the diffraction regime. The spatial current/field profile is determined from a full-wave simulation at a single and low frequency value. Our numerical results are validated through comparison to commercial simulators for very wide frequency ranges as well as with previously proposed circuit-model approaches.

Analytical circuit model for dipole frequency-selective surfaces

This contribution provides a fully analytical transmission-line circuit model for the transmission/reflection of an obliquely incident plane wave by a periodic array of printed dipoles. The topology of the equivalent circuit is rigorously derived in the analysis. In contrast with previously reported circuit models, the proposed approach accounts for dynamical effects that enable the application of the model in a very wide frequency range.

A Grounded MoM-Based Spatial Green's Function Technique for the Analysis of Multilayered Circuits in Rectangular Shielded Enclosures

A continuous counterpart of the spatial images technique is proposed for the computation of the multilayered boxed Greens functions and their derivatives. The method employs a set of auxiliary linear distribution of sources to effectively impose the potential boundary conditions along the whole cavity contour. The imposition of these boundary conditions leads to a set of integral equations (IEs), on the unknown distributions of the auxiliary sources, which are solved by applying a method of moments approach. A convergence/efficiency study, related to the test and basis functions choice, is then presented and discussed. The technique is combined with the use of dynamic ground planes generating mirror basis functions, which completely remove any singular instability. Finally, the computed Greens functions are included into a mixed-potential IE formulation for the accurate and very fast analysis of practical multilayered shielded circuits. The proposed technique does not suffer from any convergence issue and it is extremely competitive in terms of accuracy and efficiency as compared to other methods known to the authors.

Equivalent circuits for conventional and extraordinary reflection in dipole arrays

This presents an equivalent transmission-line circuit that accounts for the scattering of a TE polarized plane wave that impinges obliquely on a periodic array of metallic patches sandwiched in a dielectric slab. The proposed approach gives a very efficient reduced-order model of the electromagnetic phenomenon able to reproduce all the fine quantitative details of the reflection/transmission spectrum. Also, our model provides an easy theoretical frame to predict and/or understand all the qualitative behavior of the scattering when both oblique incidence and dielectric slabs are considered.