Fernando Quesada-Pereira

Analysis and design of periodic leaky-wave antennas for the millimeter waveband in hybrid waveguide-planar technology

This work presents a full-wave integral equation approach specifically conceived for the analysis and design of laterally-shielded rectangular dielectric waveguides, periodically loaded with planar perturbations of rectangular shape. This type of open periodic waveguide supports the propagation of leaky-wave modes, which can be used to build leaky-wave antennas which exhibit many desirable features for millimeter waveband applications. The particularities of the leaky-mode analysis theory are described in this paper, and comparisons with other methods are presented for validation purposes. Using this leaky-mode analysis method, a novel periodic leaky-wave antenna is presented and designed. This novel antenna shows some important improvements with respect to the features of previously proposed antennas. The results of the designed radiation patterns are validated with three-dimensional electromagnetic analysis using commercial software.

Frequency Steerable Two Dimensional Focusing Using Rectilinear Leaky-Wave Lenses

The concept of frequency steerable two-dimensional electromagnetic focusing by using a tapered leaky-wave line source embedded in a parallel-plate medium is presented. Accurate expressions for analyzing the focusing pattern of a rectilinear leaky-wave lens (LWL) from its constituent leaky-mode tapered propagation constant are described. The influence of the main LWL structural parameters on the synthesis of the focusing pattern is discussed. The ability to generate frequency steerable focusing patterns has been demonstrated by means of an example involving a LWL in hybrid waveguide printed-circuit technology and the results are validated by a commercial full-wave solver.

Practical Implementation of the Spatial Images Technique for the Analysis of Shielded Multilayered Printed Circuits

In this paper, a practical implementation of the spatial images technique for the analysis of shielded multilayered printed circuits inside convex cavities is proposed. A new method is introduced in order to automatically locate the images surrounding the structure in order to impose the appropriate boundary conditions for the potentials. The boundary conditions are imposed at discrete points along the cavity wall and, therefore, the technique proposed is an approximation to the exact cavity modeling. Furthermore, for the analysis of electrically long cavities, the use of several rings of images surrounding the entire cavity at different heights is employed. Using the special features of the formulation, a new method of moments implementation combined with the spatial images technique is proposed in order to efficiently analyze practical multilayered printed filters, considerably reducing the computational cost. Several examples with CPU time comparisons are provided, demonstrating the accuracy and efficiency of the new technique. A novel transversal filter in a trapezium-shaped cavity is designed, manufactured, and tested for the first time using the spatial images technique.

PAMELA: a useful tool for the study of leaky-wave modes in strip-loaded open dielectric waveguides

A software tool is presented to help in the teaching of the electromagnetic theory of open dielectric waveguides. The study of the modal spectrum of canonical closed waveguides is a basic topic in any course of electromagnetics or microwave engineering. However, surface-wave modes and leaky-wave modes in open waveguides are not yet so well known in the academic environment. Nevertheless, this study is necessary, since novel open dielectric waveguides have been proposed for millimeter-wave and optical electronics in order to reduce the conductor losses. Therefore, the comprehension of the phenomenon of leaky-wave modes and behavior is indispensable for any future microwave engineer, who has to work with the new millimeter-wave and optical technologies. This program constitutes the first tool explicitly conceived to help the teaching of the working principles of open dielectric guides loaded with printed circuits, and the associated practical leaky-wave antennas (LWAs). The code can be a very good supplement to understand how practical leaky-wave antennas work, after a basic theoretical understanding of leaky waves has been first obtained. From the appearance of leaky-wave modes in open waveguides to the design of a backward-to-forward leaky-wave antenna, some simple and very clarifying step-by-step exercises are presented to illustrate these not-so-well-known concepts. Although the program refers to a specific type of open dielectric guides (laterally-shielded, top-open, stub-loaded, rectangular dielectric waveguides with planar perturbations), the results are applicable to any open dielectric guide, helping to teach the basic theory and topics relating to leaky- and surface-wave modes in uniform and periodic structures

Transverse resonance analysis of a planar leaky wave antenna with flexible control of the complex propagation constant

In this paper an efficient technique based on the transverse resonance network has been implemented to analyze a half-mode microstrip line loaded with two rows of periodic metallic posts. For this antenna a simultaneous control of both the phase constant β and the leakage rate a is achieved and therefore a tailored radiation pattern can be synthesized whereas a high radiation efficiency is kept. The radiation mechanism is similar to the conventional microstrip leaky-wave antenna operating in its first higher-order mode, with the novelty than the leaky-mode leakage rate can be controlled thanks to the addition of the periodic metallic posts. In order to characterize the impedance associated to the row of metallic posts an electric field integral equation EFIE based on the Greens functions one dimensional periodic current filament has been solved by the method of moments MoM. Several prototypes operating at 15 GHz have been designed and validated by using a commercial full-wave simulation tool with the purpose to demonstrate the operation principle and design flexibility of this leaky-wave antenna.

Efficient optimization‐oriented design methodology of high‐order 3‐D filters using 2‐D and 3‐D electromagnetic simulators

Summary This paper proposes a computationally highly efficient interface between two-dimensional (2-D) and three-dimensional (3-D) electromagnetic (EM) simulators for the optimization-oriented design of high-order 3-D filters. In a first step, the novel optimization-oriented design methodology aligns the 3-D EM simulator response with the 2-D EM simulator response of a low-order 3-D filter by using an inverse linear space mapping optimization technique. Then, a second mapping performs a calibration with the optimal 2-D and 3-D design parameters obtained from the first mapping. The optimization of high-order filters is carried out using only the efficient 2-D EM simulator, and the calibration equations directly give the design parameters of the 3-D filter. The potential and the effectiveness of the proposed optimization-oriented design methodology are demonstrated through the design of C-band 3-D evanescent rectangular waveguide bandpass filters with increasing orders from three to eight. Copyright

Numerical evaluation of the Green's functions for arbitrarily shaped cylindrical enclosures and their optimization by a new spatial images method

This work has been developed with support from the Spanish National Project (CICYT) with reference TEC2004-04313-C02-02/TCM, and the Regional Seneca Project with reference 02972/PI/05

Numerical Evaluation of the Green's functions for Arbitrarily Shaped Enclosures

In this paper, a new spatial method has been implemented for the efficient calculation of the mixed potential Greens functions associated to electrical sources, when they are placed inside arbitrarily-shaped cylindrical cavities. The technique consists of placing electric dipole images and charges outside the cavity, imposing, at discrete points of the metallic wall, the appropriate boundary conditions for the potentials. Results show that the numerical convergence is attained fast. The cut-off frequencies and potential patterns for a trapezium-shaped waveguide are compared to those obtained by a standard finite elements technique, showing excellent agreement. Furthermore, a printed planar filter shielded in a square cavity has been analyzed with the new Greens functions, showing the practical value of the new theory.

Novel and simple technique to control the polarization in stub-loaded leaky-wave antennas

Leaky-wave antennas (LWAs) are commonly used to synthesize narrow-beam frequency-scanning radiation patterns by means of a single line-source. By properly controlling the leaky-mode propagation constant, one can flexibly design the pointing direction and the sidelobes distribution. Many studies have been performed in the last years to conceive LWAs that also have polarization flexibility, and particularly to obtain circular polarization. For this purpose, periodic arrays of slots or strips have been added to a host waveguide to induce radiation in the desired polarization. In all these LWA designs, the polarization was controlled by choosing the orientation and dimensions of the periodic perturbations. Normally, complicated orthogonal arrangements of the periodic arrays are needed to obtain circular polarization. In addition, radial waveguides and microstrip lines have also been proposed to obtain vertical and horizontal polarization at the same time, and eventually achieve a circularly polarized main beam. In this contribution, we present a totally original mechanism that allows to control the polarization of the radiated fields in stub- loaded LWAs. The proposed mechanism does not need the introduction of periodic perturbations orthogonally arranged, neither the modification of the host waveguide to obtain a radial shape. As it will be shown, a uniform LWA can be used to excite and control the horizontal and vertical components of the radiated fields.

Application of the high-gain substrate-superstrate configuration to dielectric leaky-wave antennas

The high-gain substrate-superstrate configuration, which was proposed to increase the gain in printed circuit antennas, is applied to dielectric leaky-wave antennas (LWAs) to improve its frequency response. Analysis of a slitted suspended dielectric rectangular waveguide is carried out using a full-wave method. It is proved that the minimum values of the leakage constant of the leaky-wave mode for the suspended configuration are related to the high-gain resonance conditions. Moreover, it is found that the suspended LWA exhibits very small beamwidth variations in a large frequency bandwidth. It is well-known that inhomogeneous filled LWAs suffer from variation of beamwidth as the angle of maximum radiation is scanned with frequency. The proposed topology can be adjusted so that a flat response of the beamwidth can be obtained in a large frequency band, while maintaining the frequency-scanning behavior of the LWA.