Juan Carlos Iriarte

EBG Superstrate for Gain Enhancement of a Circularly Polarized Patch Antenna

EBG enhanced antennas could advantageously replace conventional array antenna in Geo-synchronous global Earth coverage applications at S-band and lower frequencies. This new technology simplifies the antenna configuration and can potentially lead to lighter and cost effective solutions, by either eliminating or strongly simplifying the antenna beam forming network (BFN). Excellent agreement between the predictions and the measurements has been shown

Abscisic Acid Regulation of Root Hydraulic Conductivity and Aquaporin Gene Expression Is Crucial to the Plant Shoot Growth Enhancement Caused by Rhizosphere Humic Acids.

An ABA-dependent increase of root hydraulic conductivity and aquaporin expression mediates the plant shoot enhancement caused by dissolved sedimentary humic acids. The physiological and metabolic mechanisms behind the humic acid-mediated plant growth enhancement are discussed in detail. Experiments using cucumber (Cucumis sativus) plants show that the shoot growth enhancement caused by a structurally well-characterized humic acid with sedimentary origin is functionally associated with significant increases in abscisic acid (ABA) root concentration and root hydraulic conductivity. Complementary experiments involving a blocking agent of cell wall pores and water root transport (polyethylenglycol) show that increases in root hydraulic conductivity are essential in the shoot growth-promoting action of the model humic acid. Further experiments involving an inhibitor of ABA biosynthesis in root and shoot (fluridone) show that the humic acid-mediated enhancement of both root hydraulic conductivity and shoot growth depended on ABA signaling pathways. These experiments also show that a significant increase in the gene expression of the main root plasma membrane aquaporins is associated with the increase of root hydraulic conductivity caused by the model humic acid. Finally, experimental data suggest that all of these actions of model humic acid on root functionality, which are linked to its beneficial action on plant shoot growth, are likely related to the conformational structure of humic acid in solution and its interaction with the cell wall at the root surface.

Dual Circularly Polarized Broadside Beam Metasurface Antenna

This paper presents the design of a modulated metasurface (MTS) antenna capable to provide both right-hand (RH) and left-hand (LH) circularly polarized (CP) boresight radiation at Ku-band (13.5 GHz). This antenna is based on the interaction of two cylindrical-wavefront surface wave (SW) modes of transverse electric (TE) and transverse magnetic (TM) types with a rotationally symmetric, anisotropic-modulated MTS placed on top of a grounded slab. A properly designed centered circular waveguide feed excites the two orthogonal (decoupled) SW modes and guarantees the balance of the power associated with each of them. By a proper selection of the anisotropy and modulation of the MTS pattern, the phase velocities of the two modes are synchronized, and leakage is generated in broadside direction with two orthogonal linear polarizations. When the circular waveguide is excited with two mutually orthogonal TE11 modes in phase-quadrature, an LHCP or RHCP antenna is obtained. This paper explains the feeding system and the MTS requirements that guarantee the balanced conditions of the TM/TE SWs and consequent generation of dual CP boresight radiation.

Terahertz time domain spectroscopy allows contactless monitoring of grapevine water status

Agriculture is the sector with the greatest water consumption, since food production is frequently based on crop irrigation. Proper irrigation management requires reliable information on plant water status, but all the plant-based methods to determine it suffer from several inconveniences, mainly caused by the necessity of destructive sampling or of alteration of the plant organ due to contact installation. The aim of this work is to test if terahertz (THz) time domain reflectance measurements made on the grapevine trunk allows contactless monitoring of plant status. The experiments were performed on a potted 14-years-old plant, using a general purpose THz emitter receiver head. Trunk THz time-domain reflection signal proved to be very sensitive to changes in plant water availability, as its pattern follows the trend of soil water content and trunk growth variations. Therefore, it could be used to contactless monitor plant water status. Apart from that, THz reflection signal was observed to respond to light conditions which, according to a specifically designed girdling experiment, was caused by changes in the phloem. This latter results opens a promising field of research for contactless monitoring of phloem activity.

Multiband EBG navigation antenna

EBG superstrate based antenna designs can find its applications in Geosynchonous Satellite Navigation (GSN) System Antennas, since they allow to reduce the number of radiating elements while keeping the required high directivity and circular polarization. Their use will considerably simplify the feeding network and simultaneously reduce the antenna mass and volume. A dual layer EBG superstrate which can be easily tuned to the desired frequencies is presented in this paper. The design has been optimized to comply with the navigation antenna requirements of Wide Area Augmentation System (WAAS) application in L1 and L2 bands.

Experimental Validation of a Ku-Band Dual-Circularly Polarized Metasurface Antenna

The experimental validation of a Ku-band dual-circularly polarized (CP) broadside-beam metasurface (MTS) antenna is presented. A radially modulated anisotropic single-layer MTS has been synthesised employing subwavelength elliptical slotted metallic patches printed on top of a thin Arlon grounded substrate. In the structure, two decoupled phase-matched transverse magnetic and transverse electric surface waves (SWs) are excited, which interact with the modulated surface leading to a CP broadside radiation. Two different orthomode transducers have been designed to excite the SWs with orthogonal polarization and equal amplitude. The first feeding system is composed of a metallic stepped septum inside an air-filled square waveguide. A conical section is included to match the output port of the square waveguide with the terminal, dielectric filled circular waveguide. The second feed is much more compact and efficient, and it is composed of a circular waveguide completely filled by a dielectric. Depending on the input port excited on the feeds, two TE11 modes are excited with ±90° phase shift, which determine the right-hand or left-hand sense of the broadside beam generated by the MTS. Manufacturing details of the MTS and excitations are given, and the measurements are compared with the simulation results. Finally, conclusions are drawn.

Dual-pol metasurface antenna supporting transverse magnetic and electric surface waves

This work presents the characterization of a metasurface (MTS) antenna which supports two orthogonal surface waves (SWs) of transverse electric (TE) and transverse magnetic (TM) types that, at the operating frequency, propagate in the structure with the same phase velocity. The introduction of a rotationally symmetric sinusoidal modulation of the surface impedance affecting each mode enables radiation towards broadside direction. In order to obtain good polarization purity, the feeding system has to guarantee amplitude balance of the excited TM and TE SWs. Employing two orthogonal modes in phase quadrature in the feeder, right-hand (RH) or left-hand (LH) circularly polarized (CP) broadside radiation is obtained.

Generation of circularly polarized waves based on electro inductive-wave (EIW) coupling to chains of complementary split ring resonators

In this work, Electro-Inductive wave (EIW) propagation phenomenon is employed in order to introduce a polarization rotation capability in a rectangular patch antenna. The EIW propagation phenomenon is used to master the field distribution within the rectangular patch, and hence, to change the polarization of a patch antenna, which is shown to change from linear to circular polarization. EIW propagation is supported by a chain of Complementary Split Ring Resonators printed in a rectangular patch antenna at specific locations. This principle of operation is demonstrated with the design, fabrication, and measurement of antenna prototypes. Experimental results confirm numerical analysis, providing a simple antenna configuration with polarization variation capabilities, extendable to multiple configurations, in radiated waves as well as in guided wave phenomena.

Design and implementation of dual-band antennas based on a complementary split ring resonators

A simple dual-band antenna design and implementation method is proposed in this work, based on the equivalent media properties inspired by resonant metamaterial elements. The equivalent circuit model of dual-band patch antennas based on a complementary split ring resonator (CSRR) is presented and validated. The dual-band patch antenna is designed etching a CSRR in the patch of a conventional rectangular microstrip patch antenna. The first resonance is governed by the quasi-static resonance of the CSRR while the second resonance is originated by the rectangular patch. The fact of etching a CSRR on a rectangular patch antenna also produces a miniaturization of a conventional patch antenna. The equivalent circuit model proposed in this letter is sound in order to understand the functionality of dual-band patch antennas based on a CSRR. Good agreement between simulation, equivalent circuit model and experimental results is shown and discussed. These results lead the equivalent circuit model to become a simple and straightforward tool for the design of this type of multiband antennas, of low cost and versatile operation for a broad range of wireless communication systems.

Dipole antenna performance using a woodpile substrate at microwave frequencies

In this paper, a woodpile structure fabricated at microwave frequencies has been completely characterised. The improvements of the antenna characteristic when it is used as backward substrate have been proved. In particular, a good matching and much more directivity radiation pattern are obtained. Good agreement has been found between measurements and simulations.