Nonorthogonality relations between complex hybrid modes: an application for the leaky-wave analysis of laterally shielded top-open planar transmission lines

In this paper, the orthogonality relations between complex modes are investigated to demonstrate the coupling effect that exists along a transverse direction ( -axis) between TE and TM hybrid modes when power storage, loss, or leakage occur in the longitudinal direction ( -axis) of a transmission line. As an example, the parallel-plate waveguide modes are used to study a laterally shielded top-open microstrip line. The study of leaky waves is a very interesting application of the novel orthogonality relations derived in this paper. This study is carried out using the correct and incorrect orthogonality formulations, showing that physically valid results are obtained only when the orthogonality relations derived in this paper are properly introduced in the formulation. A physical explanation of this novel coupling effect between TE andTM hybrid modes with respect to the -direction is given in terms of inhomogeneous plane waves. Comparisons with previous results for a laterally shielded slot-line antenna are presented to confirm the accuracy and usefulness of this novel proposed method

Leaky and Surface Waves in Multi-Layered Laterally Shielded Microstrip Transmission Lines

In this paper the leakage effects in open laterally- shielded multilayered microstrip transmission lines are investigated. Po- tential solutions are often reported to be difficult to find, since they are located in the complex propagating factor plane. To overcome this problem, a novel iterative algorithm is implemented to relate the solu- tions in the real axis of closed transmission lines with their correspond- ing complex open structure modes. The problem of modeling the leaky behavior of the open top wall is introduced, and a mathematical and physical explanation of the solutions is proposed. The advantage of this new technique is that it allows us to easily track the leaky solutions to their final location in the complex plane. Results are presented, includ- ing the field and power patterns associated to leaky waves, showing that the derived technique is indeed effective for the study of the complex modes excited in this type of structures.Universidad Politécnica de Cartagen

Ciudad y confort ambiental: estado de la cuestión y aportaciones recientes

This paper analyses the relationships between urban climate, environmental comfort and urban planning, from the point of view of the concepts and fundamental ideas evolution, from the basic methodological contributions and from recent year’s reviews, especially in the topic of the environmental comfort indexes. The paper gives a review with highlights in the more recent contributions.En este trabajo se analizan las relaciones entre clima urbano, confort ambiental y planificación urbana desde el punto de vista de la evolución de los conceptos e ideas fundamentales, de las aportaciones metodológicas básicas realizadas y de las aplicaciones y revisiones de los últimos años, en particular en el campo de los índices de confort. Se traza, con ello, un estado de la cuestión y se destacan las aportaciones recientes más destacadas

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

IIn this paper, a spatial image technique is used to efficiently calculate the mixed potential Green’s functions associated with electric sources, when they are placed inside arbitrarily shaped cylindrical cavities. The technique is based on placing electric dipole images and charges outside the cavity region. Their strength and orientation are thencalculated by imposing the appropriate boundary conditions for the fields at discrete points on the metallic wall. A method for the assessment of the potentials accuracy is proposed, and several optimization techniques are presented. Three cavities are analyzed to demonstrate the usefulness of the techniques. The cutoff frequencies and potentials patterns are compared to those obtained by a standard finite elements technique, showing excellent agreement. Finally, a band-pass filter based on coupled lines is analyzed, demonstrating the practical value of the technique.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/0

Microstrip leaky-wave antenna with control of leakage rate and only one main beam in the azimuthal plane

An original leaky-wave antenna (LWA), conceived from a microstrip line which is laterally shielded by parallel plates, is presented in this paper. This structure shows, for the first time, that the leakage rate of a microstrip leaky-mode can be easily controlled while negligibly affecting the pointing direction. The antenna is based on the radiation from the second higher order mode of the microstrip line, which is perturbed by the addition of the two conductor walls to control the level of the leakage rate. The parallel-plates also serve as a mechanism to obtain a single main beam in the azimuthal plane, therefore improving the radiation pattern compared to common dual-beam second-higher order mode microstrip LWAs. The proposed antenna is analyzed by obtaining the corresponding leaky-mode complex propagation constant, which is calculated by a specific method of moments approach. The modal results obtained from the leaky-mode dispersion curves are validated with analysis performed on a three-dimensional structure using commercial finite element method solver. Also, a prototype is fabricated to experimentally confirm the advantages of this novel leaky-wave line source.This work was supported in part by the Spanish National project TEC2004-04313-C02-02/ TCM, in part by the Regional Seneca project 02972/PI/05, and in part by Regional Scholarship PMPDI-UPCT-2007

Printed-circuit leaky-wave antenna with pointing and illumination flexibility

A novel leaky-wave antenna, based on a periodic set of slots printed on a rectangular dielectric waveguide is conceived in this work. The antenna presents the ability to independently control the aperture illumination and the pointing direction, by only modifying the photoetched printed-circuit layout. The working mechanism is described using a leaky-mode dispersion analysis, and cosine-tapered designs are performed at 50 GHz. The radiation patterns are obtained using HFSS analysis to check the reduction of sidelobes levels, and the capacity to tune the pointing direction over a wide range of elevation angles.This work was supported by Spanish National Projects ESP2001-4546-PE, TEC2004-04313-C0202-TCM, Regional Seneca Project 2002 PB/4/FS/02, and the EPSON-Ibérica Foundation

A novel leaky-wave antenna combining an image NRD guide and a strip circuit

This letter presents a novel leaky-wave antenna which combines an image NRD (nonradiative dielectric) guide and a printed strip circuit. The proposed structure allows for an easier, cheaper and more flexible tapering mechanism than all previous leaky-wave antennas in NRD technology. The working mechanism is explained, and two different tapering strip-circuit topologies are proposed. Cosine tapered illuminations are designed using a two-dimensional leaky-mode analysis technique. Simulations with high-frequency structure simulator (HFSS) three-dimensional analysis are presented for validation purposes. Also, the influence of the feeding transitions for each printed-circuit design is studied. Results show the feasibility of one of the proposed designs, leading to a tapered radiation pattern with sidelobes level below 20 dB.This work was supported by Spanish National Projects ESP2001-4546-PE and TIC2000-0591- C03-03, and Regional Seneca Project 2002 PB/4/FS/02

Simple analysis and design of a new leaky-wave directional coupler in hybrid dielectric-waveguide printed-circuit technology

This paper presents a new theory to analyze and design a novel leaky-wave coupler based on a hybrid dielectric-waveguide printed-circuit technology. The analysis theory is based on a combined method of moments (MoM) geometrical optics (GO) technique, which makes use of the leaky mode complex propagation constant. This MoM-GO approach allows to easily obtain the response of the coupler, and to illustratively understand the working mechanism of the proposed structure. A coupler is designed to work at 5.5 GHz. Leaky mode results are compared with three-dimensional finite-element method simulations, showing the validity and accuracy of the new theory developed. This novel directional coupler presents interesting advantages when compared to previous wave couplersThis work was supported in part under Spanish National Project ESP2001-4546-PE and Spanish National Project TEC2004-04313-C02-02-TCM and under the Regional Séneca Project 2002PB/4/FS/02

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.This work was supported by Spanish National Projects ESP2001-4546-PE and TIC2000-0591- C03-03, by Regional Seneca Projects 2002 PB/4/FS/02 and PMPDI-UPCT- 2004, and by the EPSON-Ibérica Foundation

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.This work was supported by Spanish National projects ESP2001-4546-PE and TEC2004-04313-C02-02/TCM and Regional Séneca projects 2002 PB/4/FS/02. The authors would like to thank the EPSON-Ibérica Foundation for its stimulating support. and PMPDI-UPCT-2004. The authors would like to thank the EPSON-Ibérica Foundation for its stimulating support