BUSCADOR RECOLECTA

In this paper two different simple to design and easy to manufacturing transitions from a microstrip to rectangular waveguide based on ridge and groove gap waveguides are studied. The first one is based on a combination of a groove and ridge gap waveguide. In this case, the microstrip substrate occupies the whole bottom metallic housing block, namely, the transition and the gap between the bed of nails and the lid; therefore, it does not require any substrate shaping. Nevertheless, the transition needs to replace groove waveguide by ridge gap waveguide sections to avoid higher-order mode excitation. In the second approach, based on only a groove gap waveguide, the substrate is shaped to be only in the microstrip section, that is, outside the bed of nails area. This leads to a simplification of the design procedure. Prototypes of both transitions have been characterized, showing good agreement with the simulations taking into account the manufacturing tolerances. Performance comparable to the state-of-the-art in this frequency band has been achieved., This research was funded by the Spanish Ministry of Economy and Competitiveness, project numbers TEC2013-47753-C3-1-R, TEC2016-76997-C3-1-R and PID2019-109984RB-C43.

This article discusses the theory, design and practical implementation of superbackscattering antenna arrays. In analogy with Uzkov’s maximal directivity theorem, it is demonstrated that the maximal backscattering cross-section, normalized to the wavelength squared, of a linear array of N isotropic scatterers whose separation tends to zero is N2(N + 1)2=(4pi). This analytical result is validated via numerical optimization of the excitation coefficients, and the same procedure is utilized to assess the maximal backscattering of arrays of electric Hertzian dipoles (EHDs). It is found that electrically small arrays of two and three EHDs can enhance the backscattering by factors of 6.22 and 22.01, respectively, with respect to the maximum value generated by a single element. In addition, physical realizations of arrays featuring comparable enhancement factors can be straightforwardly designed by using a simple procedure inspired by Yagi-Uda antenna concepts. The practical implementations of such arrays based on copper wires and printed circuit technologies is also addressed., This work was supported in part by the Spanish Ministry of Science and
Innovation, Direccion General de Investigación y Gestión del Plan Nacional de I+D+I, Subdirección General de Proyectos de Investigación, Project No.
CSD2008-00066 and TEC2013-47753-C3-1-R, and by NSF contract number
ECCS-1126572. I.L. acknowledges financial support from a FPI scholarship
of UPNA.

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 sub-wavelength elliptical slotted metallic patches printed on top of a thin Arlon grounded substrate. In the structure, two decoupled phasematched 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 airfilled 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., The authors would like to thank financial support by the
Spanish Ministry of Science and Innovation, Direccion General
de Investigacion y Gestion del Plan Nacional de I+D+I,
Subdireccion General de Proyectos de Investigacion, Project
No. TEC2013-47753-C3-1-R and Project No. TEC2016-
76997-C3-1-R.

This paper presents the comparison of different modified Soret lenses suitable for a millimeter and submillimeterwave dualband integrated pixel detectors. The approach is based on the modification of a printed planar Soret lens, designed to operate in the sub-mm range, to obtain an antenna at the millimeter region. Three modifications of a transmission-mode Soret Lens at 850 GHz based on spiral, logarithmic and meander antennas geometries have been analyzed with a combination of Kirchhoffs Diffraction and full-wave simulation methods. The performance of the designs has been experimentally demonstrated in the submillimeterwave band, showing good agreement with simulation results., The authors would like to thank financial support by the Spanish Ministry of Science and Innovation, Project No. TEC2013-47753-C3-1-R, TEC2014-61817-EXP and TEC2016-76997-C3-1-R.

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., This research was supported by the Industry Department of the Government of Navarre (VITICS, Ref: IIM14244.RI1, project co-financed with EU funds from the ERDF) and by the Spanish Ministry of Economy and Competitiveness (BACAVID, Ref: AGL2011-30408-C04-03 and DIDAcTIc, Ref: TEC2013–47753-C3-1-R).

The physical limitations on time-harmonic scattering processes are investigated on the basis of the optical theorem. Previously derived least upper bounds on the total scattering and absorption cross-sections are obtained from it in a straightforward manner. In addition, it reveals a practical upper bound for the bistatic cross-section when evaluated in any direction. It is proved further that the maximum upper bound of the bistatic cross-section occurs in the forward scattering direction and that the corresponding upper bound for the backscattering direction is four times smaller than this maximum value. Metamaterialinspired electrically small antennas and scattering particles that approach these upper bounds are demonstrated. These examples
numerically validate the derived upper bounds, as well as illustrate the important physical principles underlying them., This work was supported in part by the Spanish Ministry of Science and Innovation, Dirección General de Investigación y Gestión del Plan Nacional
de I+D+I, Subdirección General de Proyectos de Investigación, Project Nos.
CSD2008-00066 and TEC2013-47753-C3-1-R, and by NSF contract number
ECCS-1126572.

This paper presents a planar silicon integrated subharmonic mixer on top of a photonic-crystal platform. The local oscillator (LO) power is injected through a 2D photonic crystal (PC) slab to a resonant cavity that effectively couples the signal to a planar bow-tie antenna. The same antenna, which is printed on the top of the PC cavity, contains an antiparallel Schottky diode pair which performs the down-conversion. The proposed design is a simple, easy to integrate, low cost, low profile device. Moreover, the described fabrication process is compatible with active components integration. The performance
of the design has been experimentally demonstrated showing good agreement with the simulation and is comparable with the state of-the-art of planar mixers. The work presented here is based on concepts and technologies from electronics and photonics domains and may be a good starting point for the creation of new devices, allowing the integration and upgrading of existing techniques from both worlds., The authors would like to thank financial support by
the Spanish Ministry of Science and Innovation, Dirección
General de Investigación y Gestión del Plan Nacional de I+D+I,Subdirección General de Proyectos de Investigación, Project No. TEC2013-47753-C3-1-R, TEC2014-61817-EXP and TEC2016-76997-C3-1-R.

A simplified design of an inline transition between microstrip and rectangular waveguide is presented in this paper. The transition makes use of a dielectric filled rectangular waveguide (DFRW) as an intermediate step, which simplifies manufacturing and allows for an analytical design. The behavior of the transition has been experimentally validated in the W-band by means of a back-to-back configuration. Good performance has been achieved: a return loss greaterthan 10 dB and mean insertion loss lower than 1 dB., This research was funded by the Spanish Ministry of Economy and Competitiveness, grant number
TEC2013-47753-C3-1-R and TEC2016-76997-C3-1-R

The gap waveguide technology has become an alternative to millimeter- and submillimeter-wave electronic circuit packaging thanks to the loss reduction associated with its use. In this paper, a simplified design of an inline transition between a microstrip and a groove gap waveguide (GGW) operating at the W-band is presented. The transition consists of a tapered microstrip line and a Chebyshev adapter that couple the quasi-TEM mode of the microstrip line to the so-called vertical mode of the GGW. The simplicity of this design makes this transition appropriate for monolithic microwave integrated circuit (MMIC) packaging at millimeter frequencies and above. The simulation results have been experimentally validated in the W-band. A good performance has been achieved, resulting in a return loss better than 10 dB and a mean insertion loss lower than 2 dB., This work was support by the Spanish MINECO under Project TEC2013-47753-C3-1-R and Project TEC2016-76997-C3-1R.

A real-time imaging system based on a frequency scanning antenna for conveyor belt setups is presented in this paper. The frequency scanning antenna together with an inexpensive parabolic reflector operates at the W band enabling the detection of details with dimensions in the order of 2 mm. In addition, a low level of sidelobes is achieved by optimizing unequal dividers to window the power distribution for sidelobe reduction. Furthermore, the quality of the images is enhanced by the radiation pattern properties. The performance of the system is validated by showing simulation as well as experimental results obtained in real time, proving the feasibility of these kinds of frequency scanning antennas for cost-effective imaging applications., This work was supported by the Spanish Ministry of Economy and Competitiveness Project Nos. TEC2016-76997-C3-1-R, TEC 2013-47753-C3-1-R, RTC-2014-2110-2, and postdoctoral fellowship FPDI-2013-16278.

In this paper the design of an inline transition between microstrip and groove gap waveguide operating at Wband is presented. The transition consists of two sections: a
tapered microstrip line and a Chebyshev transformer. The simplicity of this design makes this transition appropriate for MMIC packaging at millimeter frequencies and above. Experimental validation has been carried out in theW-band. Good performance has been achieved: return loss better than 10 dB and mean insertion loss lower than 2 dB., The authors would like to thank financial support by the Spanish MINECO, Project No. TEC2013-47753-C3-1-R and Project No. TEC2016-76997-C3-1-R.

In this paper a comparison between a fourth harmonic mixer and a combined doubler/subharmonic mixer based on Schottky diodes working at 300 GHz with MMIC Local Oscillator (LO) integrated in a single enclosing is presented. Both configurations allow reducing the LO requirements, since a lower LO frequency is used. In addition, the integration of the MMIC Local Oscillator with the mixer in the same single metallic block is the main novelty and advantage of this work. Since only one block is used, flange connections are avoided. This way, misalignment errors are also prevented. Besides this advantage, the compactness of this solution is also remarkable, leading to a significant weight reduction., The authors would like to thank financial support by the Spanish MINECO, Project No. TEC2013-47753-C3-1-R and Project No. TEC2016-76997-C3-1-R.

This paper presents a novel pixel geometry for the implementation of metasurfaces requiring synchronized phase propagation of transverse magnetic (TM) and transverse electric (TE) modes. The pixel is composed by an elliptical metallic patch with an asymmetric cross-shaped aperture in the center, printed on a grounded slab. A practical implementation of a metasurface was carried out employing such a pixel geometry. Simulation results show similar frequency dispersion properties for both modes within the working frequency band, in agreement with the theoretical basis., The authors would like to thank the financial support by the Spanish Ministry of Economy
and Competitiveness, Project No. TEC2013-47753-C3-1-R and TEC2016-76997-C3-1-R and by the Gobierno de
Navarra, Project PI017 COMUNICACIONES 5G and PI018 COMUNICACIONES 5G.

This paper presents the design of a modulated metasurface (MTS) antenna capable to provide both righthand (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., This work was supported by COST ACTION IC1102, NEWFOCUS
Research Networking Program and Spanish Ministry of Science and
Innovation (project TEC2013-47753-C3-1-R).