José Luis Gómez-Tornero

Design of tapered leaky-wave antennas in hybrid waveguide-planar technology for millimeter waveband applications

Different types of waveguide leaky-wave antennas, asymmetrically perturbed with printed-circuits, are studied in this paper. The capability to modify the leakage constant of the excited leaky-wave mode, while maintaining unchanged its phase constant, is studied in detail for each design. Several slot and strip configurations are proposed, in which the width and the position of the planar printed circuit perturbation is modified along the length of the antenna to obtain different tapering topologies. All of them are mechanically flexible to realize, thus simplifying the manufacturing process for millimeter wavelengths applications. The two-dimensional method used for the analysis is accurate for any geometry of the planar perturbation, and also allows for the computation of the whole spectrum of modes in these open waveguides. This makes possible to predict the appearance of unwanted channel-guide modes, and also allows for the study of the coupling effect between the desired leaky-wave mode and them. A tapered design is performed and compared with full-wave three-dimension simulations to validate the proposed technology.

Planar Leaky-Wave Antenna With Flexible Control of the Complex Propagation Constant

This communication demonstrates for the first time the capability to independently control the real and imaginary parts of the complex propagation constant in planar, printed circuit board compatible leaky-wave antennas. The structure is based on a half-mode microstrip line which is loaded with an additional row of periodic metallic posts, resulting in a substrate integrated waveguide SIW with one of its lateral electric walls replaced by a partially reflective wall. The radiation mechanism is similar to the conventional microstrip leaky-wave antenna operating in its first higher-order mode, with the novelty that the leaky-mode leakage rate can be controlled by virtue of a sparse row of metallic vias. For this topology it is demonstrated that it is possible to independently control the antenna pointing angle and main lobe beamwidth while achieving high radiation efficiencies, thus providing low-cost, low-profile, simply fed, and easily integrable leaky-wave solutions for high-gain frequency beam-scanning applications. Several prototypes operating at 15 GHz have been designed, simulated, manufactured and tested, to show the operation principle and design flexibility of this one dimensional leaky-wave antenna.

Anisotropic Impedance Surfaces for Linear to Circular Polarization Conversion

Anisotropic impedance surfaces are employed as low-profile and broadband reflectors that convert orthogonal linear to right- and left-handed circular polarization respectively. By virtue of anisotropy, it is possible to independently control the reflection characteristics of two orthogonal linearly polarized incident plane waves and therefore achieve linear to circular polarization conversion. Equivalent circuits for anisotropic impedance surfaces with arbitrarily shaped elements are employed to demonstrate the operating principle and a design procedure is proposed. The proposed design procedure is demonstrated by means of an example involving a dipole array. A prototype is designed and its performance characteristics are evaluated. The 3-dB relative axial ratio bandwidth exceeds 60%, while low loss and angular stability are also reported. Numerical and experimental results on a fabricated prototype are presented to validate the synthesis and the performance.

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.

Holographic Pattern Synthesis With Modulated Substrate Integrated Waveguide Line-Source Leaky-Wave Antennas

We present the synthesis of one-dimensional (line-source) leaky-wave antennas (LWAs) in substrate integrated waveguide (SIW) technology with modulated geometry, demonstrating the capability to flexibly tailor the radiated fields pattern, both in nearand far-field regimes. The synthesis technique is inspired in holographic concepts, which are related to the existence of modulated leaky waves. A systematic design algorithm to obtain the requested modulation of the SIW width and distance between posts to synthesize the desired radiation pattern is described. Several design examples operating at 15 GHz are reported and experimentally validated, showing the power and versatility of the proposed holographic SIW technology.

Holographic Surface Leaky-Wave Lenses With Circularly-Polarized Focused Near-Fields—Part I: Concept, Design and Analysis Theory

A novel concept of planar printed-circuit microwave lens, based on the transformation of a cylindrical surface wave into a modulated leaky wave, is presented in this paper. Inspired on holographic concepts, the TM0 cylindrical leaky wave is properly tapered across the two-dimensional surface by using an Archimedean-spiral shaped slotted printed-circuit, so that it is obtained a quadratic-phase, quasi-uniform amplitude aperture distribution which creates a highly focused circularly-polarized near-field pattern. The first part of this paper describes the general analysis and synthesis methodology to obtain planar holographic lenses with high radiation and focusing efficiency. As an example, a printed-slot lens with 6λ0 diameter and focal ratio F/D = 1 operating at 10 GHz is designed and theoretically studied by simulations. The second part of the paper concentrates on the prototype and measurements.

Control of Leaky-Mode Propagation and Radiation Properties in Hybrid Dielectric-Waveguide Printed-Circuit Technology: Experimental Results

Experimental results are presented to show how a planar circuit, printed on a laterally shielded dielectric waveguide, can induce and control the radiation from a leaky-mode. By studying the leaky-mode complex propagation constant, a desired radiation pattern can be synthesized, controlling the main radiation characteristics (pointing direction, beamwidth, sidelobes level) for a given frequency, This technique leads to very flexible and original leaky-wave antenna designs. The experiments show to be in very good agreement with the leaky-mode theory

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.

Electronic Full-Space Scanning With 1-D Fabry–Pérot LWA Using Electromagnetic Band-Gap

A novel mechanism to obtain full-space electronic scanning from a half-space scanning one-dimensional (1-D) Fabry-Pérot (FP) leaky-wave antenna (LWA) is proposed and experimentally demonstrated in this letter. By using a central feed that divides the structure into two independently controlled leaky lines, one each side, and making use of the electromagnetic band-gap (EBG) region of the FP resonator, the antenna can be electronically tuned to operate in three different regimes: backward scanning, forward scanning, and broadside radiation. Leaky-mode dispersion theory and experimental results of a fabricated prototype demonstrate a continuous electronic scanning from -25° to +25° at 5.5 GHz.

Analysis and Design of Conformal Tapered Leaky-Wave Antennas

The theory to analyze and design tapered conformal line-source leaky-wave antennas is described in this letter. The deformation in the radiation pattern associated to the bending of the antenna is accurately predicted, and useful expressions are derived to taper the leaky-mode complex propagation constant in order to restore the high-directive radiated beam scanning at the desired angle. The analysis method and the design approach are validated with full-wave simulations of a curved tapered leaky-wave antenna in hybrid technology.