Grating Lobes Reduction Using a Multilayer Frequency Selective Surface on a Dual-Polarized Aperture Array Antenna in Ka-Band

[EN] This paper presents a multilayer frequency selective surface for a dual-polarized aperture array antenna in Ka-band. The elements of the array are cylindrical open cavities with a diameter of at 30 GHz, and spaced one wavelength. Due to this separation between elements, which is limiting and not reducible by the architecture of the feeding network and the size of the radiating element, grating lobes appear. Frequency Selective Surfaces (FSS) can be a solution to this problem without modifying the feeder architecture nor the radiating elements. This paper presents the FSS design for reducing grating lobes level, the antenna assembly, and the experimental validation. The full antenna performance demonstrates that FSS operates in a range identical to the feeder (29.5 GHz to 31 GHz) with the added benefit of reducing the grating lobes level more than 10 dB for both polarizations.This work was supported by the Spanish Ministry of Economy and Competitiveness (Ministerio de Economia y Competitividad) under Project TEC2016-79700-C2-1-R.Sánchez-Escuderos, D.; Ferrando-Rocher, M.; Herranz Herruzo, JI.; Valero-Nogueira, A. (2020). Grating Lobes Reduction Using a Multilayer Frequency Selective Surface on a Dual-Polarized Aperture Array Antenna in Ka-Band. IEEE Access. 8:104977-104984. https://doi.org/10.1109/ACCESS.2020.3000069S104977104984

Periodic Leaky-Wave Antenna on Planar Goubau Line at Millimeter-Wave Frequencies

A periodic leaky-wave antenna on a planar Goubau line is presented. This transmission line is formed by a planar single-wire waveguide on a thin dielectric substrate. Leakage is produced by adding dipoles along the line on the bottom face of the substrate. A coplanar waveguide is used to feed the antenna, which acts as a smooth transition between the input coaxial cable and the planar Goubau line. The advantage of using this line lies on its losses, lower than those of typical microstrip lines due to the absence of a ground plane. As a result, a higher radiation efficiency than in microstrip-fed antennas can be obtained while keeping similar advantages, e.g., low profile or low production cost. A prototype of the antenna at 40 GHz has been fabricated. Measurements of this prototype are presented in this letter.This work was supported by the Spanish Ministry of Education and Science (Ministerio de Educacion y Ciencia) under Projects TEC2010-20841-C04-01 and CSD2008-00068.Sánchez Escuderos, D.; Ferrando Bataller, M.; Herranz Herruzo, JI.; Cabedo Fabrés, M. (2013). Periodic Leaky-Wave Antenna on Planar Goubau Line at Millimeter-Wave Frequencies. IEEE Antennas and Wireless Propagation Letters. 12:1006-1009. https://doi.org/10.1109/LAWP.2013.2278035S100610091

Dual Circularly-Polarized Slot-Array Antenna in Ka-Band fed by Groove Gap Waveguide

[EN] A dual circularly-polarized slot-array antenna fed by a Groove Gap Waveguide (GGW) and operating in the KaBand is presented in this paper. A simple mechanism is proposed to switch the polarization, from RHCP to LHCP, and viceversa. The lid of the antenna has two pieces: one fixed and one sliding. The fixed piece hosts T-shaped slots, and the sliding block is in charge of adjusting the offset of the perpendicular grooves with respect to the longitudinal slots. Preliminary results show an axial ratio below 1.5 dB for both, RHCP and LHCP, within a bandwidth of 1 GHz centered at 30 GHz.This work has been supported by the Spanish Ministry of Science, Innovation and Universities (Ministerio de Ciencia, Innovacion y Universidades) under project TEC2016-79700-C2-1-R.Ferrando-Rocher, M.; Herranz Herruzo, JI.; Sánchez-Escuderos, D.; Valero-Nogueira, A. (2020). Dual Circularly-Polarized Slot-Array Antenna in Ka-Band fed by Groove Gap Waveguide. IEEE. 421-422. https://doi.org/10.1109/IEEECONF35879.2020.9329473S42142

True-Time-Delay Mechanical Phase Shifter in Gap Waveguide Technology for Slotted Waveguide Arrays in Ka-band

This paper proposes a novel all-metal mechanical phase shifter in gap waveguide technology. The phase shifter is aimed at providing beam-scanning capabilities to conventional slot array antennas along the elevation plane. To validate experimentally the beam-steering functionality, a 4×8 slot-array antenna has been designed and fabricated, along with the phase-shifting mechanism. The whole antenna consists of two pieces: a lower rotatable block, which changes the length of concentric Groove Gap Waveguides, and an upper fixed block, where the slot-array antenna is placed. Experimental results validate the proposed concept, having obtained steering angles of up to 25∘, with gain levels around 20 dBi with an antenna efficiency close to 90%. A reflection coefficient below –10 dB is achieved for a wide range of rotation angles from 29.5 GHz to 30.5 GHz. The proposed phase shifter is completely scalable to any array size and its true-time-delay nature enables wide steering ranges for closely-spaced slot arrays with wideband radiation performance.This work was supported by the Spanish Ministry of Economics and competitiveness under project TEC2016-79700-C2-1-R

Mechanical phase shifter in gap-waveguide technology

[EN] This contribution presents a low-loss mechanical phase shifter in gap-waveguide technology. The phase shifter is aimed at ground terminals for Ka-band satellite on-the-move applications. The use of the gap-waveguide technology allows to divide the device into two main blocks distributed in two levels: a lower-rotatable block, in charge of the power distribution and the phase shifting; and an upper-fixed block with the output waveguides. In this paper, the lower and upper blocks are designed using Groove-gap waveguides (GGW), and Ridge-gap waveguides, respectively, connected to each other by coupling slots. Results show a good performance within the operating frequency band in terms of the phase shift between consecutive output ports (suitable for array feeding), and the return loss level at the input port.This work has been supported by the Spanish Ministry of Science, Innovation and Universities (Ministerio de Ciencia, Innovacion y Universidades) under project TEC2016-79700- C2-1-R.Sánchez-Escuderos, D.; Herranz Herruzo, JI.; Ferrando-Rocher, M.; Valero-Nogueira, A. (2020). Mechanical phase shifter in gap-waveguide technology. IEEE. 1-5. https://doi.org/10.23919/EuCAP48036.2020.9135719S1

A Novel Circularly-Polarized T-shaped Slot Array Antenna in Ka-band

[EN] A T-shaped slot-array antenna fed through a Groove Gap Waveguide (GGW) is presented in this paper. The array antenna operates at 30 GHz. The way the slots are excited, along with the T-shape on its lid allows a compact single-layer architecture. A uniform linear array of 12 elements is designed to demonstrate the viability of this concept for high-efficient singlelayer slot-array antennas. Preliminary results show a frequency bandwidth of 1 GHz with input reflection coefficient better than ¿12 dB. In addition, being a full-metal antenna, the expected efficiency is high. It is worth stressing the good polarization purity achieved, being below 1.5 dB within the band of interest.This work has been supported by the Spanish Ministry of Science, Innovation and Universities (Ministerio de Ciencia, Innovacion y Universidades) under project TEC2016-79700-C2-1-R.Ferrando-Rocher, M.; Herranz Herruzo, JI.; Sánchez-Escuderos, D.; Valero-Nogueira, A. (2020). A Novel Circularly-Polarized T-shaped Slot Array Antenna in Ka-band. IEEE. 1-3. https://doi.org/10.23919/EuCAP48036.2020.9135490S1

Low-loss Circularly Polarized Periodic Leaky-Wave Antenna

(c) 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other worksThis letter presents a periodic leaky-wave array antenna with circular polarization at millimeter-wave frequencies. The antenna is designed on the low-loss planar Goubau transmission line to maximize the radiation efficiency of the antenna. The unit cell of the array is formed by four dipoles located on both faces of the Goubau line s substrate. A prototype has been fabricated and measured. Experimental results show an impedance bandwidth above 15% for S11 < - 10 and a 3-dB axial-ratio bandwidth of 7.6%. The radiation efficiency and maximum gain of the prototype are above 90% and 15.6 dBi, respectively, from 38 to 41 GHz. The maximum gain and the minimum axial ratio present the characteristic steering behavior of leaky-wave antennas.This work was supported by the Spanish Ministry of Education and Science (Ministerio de Educacion y Ciencia) under Projects TEC2010-20841-C04-01, TEC2013-47360-C3-3-P, and CSD2008-00068.Sánchez-Escuderos, D.; Ferrando Bataller, M.; Herranz Herruzo, JI.; Rodrigo Peñarrocha, VM. (2016). Low-loss Circularly Polarized Periodic Leaky-Wave Antenna. IEEE Antennas and Wireless Propagation Letters. 15:614-617. https://doi.org/10.1109/LAWP.2015.2463672S6146171

Fire resilience and forest restoration in Mediterranean fire-prone areas

Mediterranean ecosystems are of importance worldwide because they are biodiversity hot spots. In these areas, forest fires have been modelling the landscape since the Pleistocene Era. Consequently, plant communities inhabiting this fire-prone area have developed adaptive traits (e.g. serotiny) or life-history strategies to persist, exhibiting a high degree of survival or recovering after frequent fires or other disturbances, such as severe drought. In general, this implies high resilience, but in recent years aridity and fire dynamics have been increasing due to global climate change, which has strongly affected the Mediterranean Basin. These changes are inducing higher risks of soil loss and lower plant productivity in the long term, which influences the resilience of the community present before the disturbance. Some species are pirophytes (fire adapted), such as Cistus sp. (Ferrandis et al., 1999a), or pirophyles (fire dependant). Pinus halepensis Mill. and some populations of Pinus pinaster Aiton have been catalogued as pirophylous species. They are not promoted by fire (Martínez-Sánchez et al., 1996) but show colonizer behavior in the absence of fire (Ayari et al., 2011). The main four components of resilience are elasticity (recovery rate), amplitude (fire severity inducing no recovery), malleability (differences from the previous state) and damping (oscillation of ecosystem parameters). If the plant community does not recover after disturbance or natural characteristics do not achieve forest planning objectives, restoration and stand improvement through forest management are important choices for lowering the aridity risk

Optimization of the E-plane loaded rectangular waveguide for low-loss propagation

The insertion of vertical slabs in a metallic rectangular waveguide distorts the power distribution of the waveguide, producing new modes and modifying the existing ones. The resulting waveguide, known as E-plane loaded rectangular waveguide, is studied in this paper, focusing the attention on the TE-type modes in a symmetrical case. A quasi-TE10 is found which may confine the energy in the central air region by suitably choosing the dielectric slabs' dimensions. An algorithm to optimize these dimensions is proposed in order to maximize the confinement of power in the air region and minimize the attenuation of the mode. This minimization is specially important at high frequencies, where the ohmic losses and the dielectric absorption become extremely high. This paper includes an example at THz frequencies and presents the design of several devices using the E-plane loaded rectangular waveguide.This work has been supported by the Spanish Ministry of Science and Innovation (Ministerio de Ciencia e Innovacion) under the projects TEC2010-20841-C04-01 and CSD2008-00068.Sánchez Escuderos, D.; Ferrando Bataller, M.; Herranz Herruzo, JI.; Baquero Escudero, M. (2013). Optimization of the E-plane loaded rectangular waveguide for low-loss propagation. Progress In Electromagnetics Research. 135:411-433. https://doi.org/10.2528/PIER12102305S41143313