Full Professor (2006) from the Department of Electrical and Computer Engineering (DEEC) of Instituto Superior Técnico (IST), faculty of Engineering from the University of Lisbon. PhD degree in Electrical and Computer Engineering in 1990. Research work spans millimeter-wave antennas for broadband communication systems including satellites, antennas for the internet of things based on RFID and UWB technology, antennas for body-area applications including medical applications, and metamaterials.
Vaquero, Á.F.; Pino, M.R.; Arrebola, M.; Matos, S.A.; Costa, J.R.; Fernandes, C.A. Evaluation of a Dielectric-Only Transmitarray for Generating Multi-Focusing Near-Field Spots Using a Cluster of Feeds in the Ka-Band. Sensors 2021, 21, 422., Jan 2001
A transmitarray antenna is evaluated to generate a multi-focusing spot area in the Fresnel region... more A transmitarray antenna is evaluated to generate a multi-focusing spot area in the Fresnel region of the antenna in the Ka-band. The antenna is designed to focus the radiated field at a certain point using a central feeding configuration. The number of feeds is increased to create as many focusing spots as feeds. The feeds are placed along an arc defined in the principal planes of the transmitarray, radiating independent near-field spots and providing a solution with a wide-angle spot scanning without an antenna displacement and a high isolation between feeds. To validate this concept, a transmitarray based on dielectric-only cells is designed and simulated under full-wave conditions. Then, this design is manufactured using a 3D printing technique, and the prototype is measured in a planar acquisition range. Measurements are performed for different feed positions in order to validate the multi-focusing capability of the antenna. Measurements and simulations show a high agreement and validate the proposed design technique.
IEEE Transaction on Antennas and Propagation, 2018
— Many wireless communication applications such as satellite communications use circularly polari... more — Many wireless communication applications such as satellite communications use circularly polarized (CP) signals, with the requirement for easy switching of the polarization sense between uplink and downlink. Specifically, in satellite communications , the trend is also to move to higher frequencies and integrate the receiving and transmitting antennas in one dual-band terminal. However, these simultaneous demands make the design and fabrication of the composing parts very challenging. We propose, here, a dual-band dual-linear polarization (LP)-to-CP converter that works in the transmission mode. The working principle of this polarizer is explained through an example for Ka-band satellite communications at 19.7–20.2 and 29.5–30 GHz. The LP-to-CP converter is a single panel composed of identical unit cells with a thickness of only 1.05 mm and a size of 5.3 mm × 5.3 mm. Due to its operation in the transmission mode, the polarizer can be combined with a simple dual-band dual-LP antenna to obtain the desired dual-band dual-CP single antenna. However, the unique property of this polarizer is yet the fact that it converts a given LP wave, e.g., x-polarization, to orthogonal CP waves at the two nonadjacent frequency bands, e.g., left-handed CP at lower band and right-handed CP at higher band. The polarizer is tested both with 20 and 30 GHz LP rectangular horns to illuminate a dual-band transmit array (TA) to obtain wide-angle steering of CP beams. The performance of the polarizer and its association with the TA is evaluated through simulation and measurements. We also present design guidelines for this type of polarizer. Index Terms— Antenna–filter–antenna, circular polarization (CP), dual-band antennas, frequency selective surfaces, periodic structures, polarization conversion.
Surface plasmons polaritons are collective excitations of an electron gas that occur at an interf... more Surface plasmons polaritons are collective excitations of an electron gas that occur at an interface between negative-ε and positive-ε media. Here, we report the experimental observation of such surface waves using simple waveguide metamaterials filled only with available positive-ε media at microwave frequencies. In contrast to optical designs, in our setup the propagation length of the surface plasmons can be rather long as low loss conventional dielectrics are chosen to avoid typical losses from negative-ε media. Plasmonic phenomena have potential applications in enhancing light– matter interactions, implementing nanoscale photonic circuits and integrated photonics.
In this paper, we propose a ball grid array (BGA) module with an integrated 3-D-printed plastic l... more In this paper, we propose a ball grid array (BGA) module with an integrated 3-D-printed plastic lens antenna for application in a dedicated 130 GHz OOK transceiver that targets the area of 5G backhaul/fronthaul systems. The main design goal was the full integration of a small footprint antenna with an energy-efficient transceiver. The antenna system must be compact and cost effective while delivering an approximately 30 dBi gain in the working band, defined as 120 to 140 GHz. Accordingly, a 2 × 2 array of aperture-coupled patch antennas was designed in the 7 × 7 × 0.362 mm 3 BGA module as the feed antenna of the lens. This achieved a 7.8 dBi realized gain, broadside polarization purity above 20 dB, and over 55% total efficiency from 110 to 140 GHz (20% bandwidth). A plastic elliptical lens 40 mm in diameter and 42.3 mm in height was placed on top of the BGA module. The antenna achieved a return loss better than −10 dB and a 28 dBi realized gain from 114 to 140 GHz. Finally, active measurements demonstrated a >12 Gbps Tx/Rx link at 5 m with bit error rate (BER) < 10 −6 at 1.6 pJ/b/m. These results pave the way for future cost-effective, energy-efficient, high-data rate backhaul/fronthaul systems for 5G communications. Index Terms— 3-D printing, 5G, backhaul/fronthaul links, ball grid array (BGA), dielectric lens, millimeter-wave (mmw) antennas, organic module.
Transmit array design is more challenging for dual-band operation than for single band, due to th... more Transmit array design is more challenging for dual-band operation than for single band, due to the independent 360° phase wrapping jumps needed at each band when large electrical length compensation is involved. This happens when aiming at large gains, typically above 25 dBi with beam scanning and F/ D ≤ 1. No such designs have been reported in the literature. A general method is presented here to reduce the complexity of dual-band transmit array design, valid for arbitrarily large phase error compensation and any band ratio, using a finite number of different unit cells. The procedure is demonstrated for two offset transmit array implementations operating in circular polarization at 20 GHz(Rx) and 30 GHz(Tx) for Ka-band satellite-on-the-move terminals with mechanical beam-steering. An appropriate set of 30 dual-band unit cells is developed with transmission coefficient greater than −0.9 dB. The full-size transmit array is characterized by full-wave simulation enabling elevation beam scanning over 0°−50° with gains reaching 26 dBi at 20 GHz and 29 dBi at 30 GHz. A smaller prototype was fabricated and measured, showing a measured gain of 24 dBi at 20 GHz and 27 dBi at 30 GHz. In both cases, the beam pointing direction is coincident over the two frequency bands, and thus confirming the proposed design procedure.
This paper illustrates the role of additive manufacturing (AM) as enabling technology to realize ... more This paper illustrates the role of additive manufacturing (AM) as enabling technology to realize high-performance low-cost antennas for Ka-band applications. In addition to the inherent electromagnetic challenges implicit in the conception of such complex devices, this paper also points out the stringent limitations that appear when opting for classical fabrication techniques, based on assembled split-block models. AM emerges in this context as a change of paradigm, allowing mono-lithic fabrication and design freedom, which result in substantial improvements in terms of compactness, mass, simplicity, cost, and production time. Two different antennas for Ka-band satellite communications are presented here, namely a wideband horn and a dual-band circular cavity. Both prototypes are fabricated using a stereolithographic (SLA) AM process followed by metal coating. This fabrication approach is especially well suited to the implementation of these designs, since they have internal shapes that are inaccessible to conventional machining tools. The experimental results are not only in very good agreement with the theoretical predictions but also demonstrate improvements over the performances achieved by traditional milling and assembly fabrication approaches, thereby confirming the validity and great potential of SLA for Ka-band satellite communications.
A shaped double-shell dielectric lens is evaluated as a primary feed for a multibeam single-refle... more A shaped double-shell dielectric lens is evaluated as a primary feed for a multibeam single-reflector system operating in the satellite uplink and downlink Ka-bands, complying with gain and edge-of-coverage (EoC) directivity requirements. An assembly of dual-band printed feeds is integrated at the base of a single lens, each feed producing a virtual focus far behind the lens base and coincident with the reflector focal arch. The used double-shell lens approach, instead of a single-material lens, allows an extra degree of freedom to accommodate an aberration mitigation condition. This primary feed system is proposed as a low-complexity solution to enable fitting more beams per solid angle than conventional single-feed-per-beam systems based on a cluster of focal-plane horns. A proof-of-concept lens prototype with 87 mm diameter and 62 mm height, fed by a linear arrangement of five dual-band printed feeds, was fabricated and tested at the Ka-band. The lens measured radiation patterns were post-processed to evaluate the combined performance of the lens with an offset F/D 1 reflector system designed for 45-dBi EoC directivity. It is shown that it duplicates the reflector aperture efficiency compared to horn-fed systems with same feed separation. Index Terms—Dual-band antenna, multibeam antennas, reflector antennas, shaped double shell-lens antenna.
We successfully assess the feasibility of a passive body-implantable sensor antenna concept to re... more We successfully assess the feasibility of a passive body-implantable sensor antenna concept to reach 750 Mbps using impulse radio (IR) in the near-field. It is based on a uniplanar printed antenna configuration, operating in the 1.4-to 4.2-GHz band. The analysis includes the effect of the implant media, the performance in terms of data rate transmission (theoretical and experimental) and feasibility of a " passive " sensor concept in terms of power constraints associated with specific absorption rate (SAR) limits, Federal Communications Commission (FCC) power mask, energy scavenging circuit minimum activation energy, and signal-to-noise ratio (SNR). Finally, we prove the potential of the overall system integrated with an electronic chip model and bio-compatible material. To our knowledge there is no explicit study in the literature that fully demonstrates an implantable system with this kind of data rates addressing all the above. Index Terms—Body-area communication, high data rates, impulse radio (IR), link power budget, passive antenna, phantom, pulse fidelity, specific absorption rate (SAR).
A ball grid array-module (BGA-module) incorporating a low-cost shaped dielectric lens is proposed... more A ball grid array-module (BGA-module) incorporating a low-cost shaped dielectric lens is proposed for wireless communications in the 60-GHz WiGig band between a smart eye-wear, where it is integrated and facing a laptop or TV. The module, which is codesigned with a 60-GHz transceiver, consists of two separate identical antennas for transmitting (Tx) and receiving (Rx). The in-plane separation of these elements is 6.9 mm both being offset from the lens focus. This poses a challenge to the lens design to ensure coincident beam pointing directions for Rx and Tx. The shaped lens is further required to narrow the angular coverage in the elevation plane and broaden it in the horizontal plane. A 3-D-printed eyewear frame with an integrated lens and a recess for proper BGA-module integration is fabricated in ABS-plastic material. Measurements show a reflection coefficient below −12 dB in the 57–66 GHz band. A maximum gain of 11 dBi is obtained at 60 GHz, with 24 • and 96 • beamwidth at 5-dBi gain, respectively, in the vertical and horizontal planes. The radiation exposure is evaluated for a homogeneous SAM head phantom and a heterogeneous visible human head. The simulated power density values for both models are found to be lower than the existing standards.
A simple mechanical beam steering antenna concept is proposed for ground mobile terminals of Ka-b... more A simple mechanical beam steering antenna concept is proposed for ground mobile terminals of Ka-band satellite and high altitude platform (HAP) providing broadband access services. The wide-angle elevation beam steering is achieved by in-plane translation of a thin offset flat lens in front of a stationary primary feed while full azimuth coverage is obtained by simple 360º rotation of the lens. A new strategy is also proposed to reduce the effective F/D of the focusing system and consequently the total antenna height without increasing beam distortion: a second small flat lens is added on top of the primary feed to create a virtual focus located well below the feed phase center. The challenge is to conciliate high gain both with wide beam scanning and reduced antenna height. Design rules are presented for this antenna concept along with a 27.3-dBi gain fabricated example for the up-link Ka-band (29.5–30 GHz), with circular polarization, 0◦ to 50◦ 20 elevation scan, better than 2.8-dB scan loss and an effective F/D of only 0.55. Both lenses are 3.35-mm thick, formed by a suitable assembly of phase shifting unit cells with less than 0.4 dB of transmission loss in simulation. The main lens dimensions are 195 mm × 145 mm and its weight is 215 g. Total antenna height, including the feed is 26 84 mm.
The design of a micromachined polyethylene lens for WiGig modules is described and its electromag... more The design of a micromachined polyethylene lens for WiGig modules is described and its electromagnetic characteristics are measured. The lens is electromagnetically fed by linearly polarized Tx and Rx patch antennas integrated in an existing ball-grid-array (BGA) organic module. Antennas are separated from each other by a distance of 4.45 mm (0.89lambda at 60 GHz). The goal of the lens is to increase the gain of each antenna while lowering the beam depointing effect due to their offset position regarding the focal point of the lens. A geometrical optics/physical optics (GO/PO) hybrid method is applied to the design and analysis of the lens shape for noncollimating purpose. Using a lens height of 30 mm for both Tx and Rx antennas, a 13-dBi minimum realized gain from 54 to 66 GHz is obtained. Compared to an elliptical lens providing an equivalent realized gain over the same bandwidth, the depointing angle from the boresight direction is reduced from 15° to 4°. Full-wave simulations are verified by measurements.
A complete UHF radio-frequency identification (RFID)-based system capable of localizing individua... more A complete UHF radio-frequency identification (RFID)-based system capable of localizing individual blood bags inside storage cabinet drawers is presented. It was developed to demonstrate the improvement possibility of current blood stock management systems and as the submission to the 2014 IEEE AP-S Student Design Contest: Antennas for RFID Application. The system is composed of a cabinet model, a transceiver unit, and a PC with the controlling software. A new implementation of pseudolocalization principle is used to localize the blood bags that are equipped with dedicated passive tags designed to be resilient to blood proximity and small size. The detector antennas are placed at the drawers bottoms and additional passive tags are utilized to identify individual locations in each drawer. The transceiver unit is made from off-the-shelf commercial electronic boards and wirelessly controlled by software run on the PC. The entire system is small, transportable, battery powered, and low cost.
A simple low-cost mobile ground terminal antenna for Ka-band satellite communications is presente... more A simple low-cost mobile ground terminal antenna for Ka-band satellite communications is presented. The antenna is composed of a shaped dielectric lens which tilts and rotates in front of a feed to direct the beam. The wideband feed system is composed of a quad-ridged horn with a 45° slant aperture and a coaxial-to-quad-ridged circular waveguide transition. The lens allows simple mechanical beam steering from 0° to 65° in relation to the zenith and 360° in azimuth by rotating both the lens and the feed slanted aperture. Performance measurements of a manufactured prototype prove the beam tilting capabilities in elevation with a maximum gain of 22 dBi and scan loss below 3 dB at 20 GHz and 24 dBi gain with less than 4.5 dB scan loss at 30 GHz.
Starting from a challenge in the early 1990s to develop a highly shaped beam dielectric lens ante... more Starting from a challenge in the early 1990s to develop a highly shaped beam dielectric lens antenna for a pilot 150 Mb/s cellular mobile broadband system operating in the 60-GHz band, several new developments have been accomplished over more than 20 years at Instituto de Telecomunicações [1] in the areas of millimeter-wave shaped dielectric lens antennas and planar metamaterial lenses. We review here a few representative examples with numerical and experimental results, covering applications in mobile broadband communications, radiometry, satellite communications, multigigabit short-range communications, and sublambda near-field target detection.
Dielectric lens antennas are proposed for wireless broadband communication systems in the mm-wave... more Dielectric lens antennas are proposed for wireless broadband communication systems in the mm-wave range. Two lens antenna configurations for base station applications are presented and evaluated in terms of radiation characteristics, feeding system, input reflection loss, bandwidth and fabrication tolerances. The system requirements to provide optimum power distribution over the cell and good control of the cell boundaries are achieved.
Vaquero, Á.F.; Pino, M.R.; Arrebola, M.; Matos, S.A.; Costa, J.R.; Fernandes, C.A. Evaluation of a Dielectric-Only Transmitarray for Generating Multi-Focusing Near-Field Spots Using a Cluster of Feeds in the Ka-Band. Sensors 2021, 21, 422., Jan 2001
A transmitarray antenna is evaluated to generate a multi-focusing spot area in the Fresnel region... more A transmitarray antenna is evaluated to generate a multi-focusing spot area in the Fresnel region of the antenna in the Ka-band. The antenna is designed to focus the radiated field at a certain point using a central feeding configuration. The number of feeds is increased to create as many focusing spots as feeds. The feeds are placed along an arc defined in the principal planes of the transmitarray, radiating independent near-field spots and providing a solution with a wide-angle spot scanning without an antenna displacement and a high isolation between feeds. To validate this concept, a transmitarray based on dielectric-only cells is designed and simulated under full-wave conditions. Then, this design is manufactured using a 3D printing technique, and the prototype is measured in a planar acquisition range. Measurements are performed for different feed positions in order to validate the multi-focusing capability of the antenna. Measurements and simulations show a high agreement and validate the proposed design technique.
IEEE Transaction on Antennas and Propagation, 2018
— Many wireless communication applications such as satellite communications use circularly polari... more — Many wireless communication applications such as satellite communications use circularly polarized (CP) signals, with the requirement for easy switching of the polarization sense between uplink and downlink. Specifically, in satellite communications , the trend is also to move to higher frequencies and integrate the receiving and transmitting antennas in one dual-band terminal. However, these simultaneous demands make the design and fabrication of the composing parts very challenging. We propose, here, a dual-band dual-linear polarization (LP)-to-CP converter that works in the transmission mode. The working principle of this polarizer is explained through an example for Ka-band satellite communications at 19.7–20.2 and 29.5–30 GHz. The LP-to-CP converter is a single panel composed of identical unit cells with a thickness of only 1.05 mm and a size of 5.3 mm × 5.3 mm. Due to its operation in the transmission mode, the polarizer can be combined with a simple dual-band dual-LP antenna to obtain the desired dual-band dual-CP single antenna. However, the unique property of this polarizer is yet the fact that it converts a given LP wave, e.g., x-polarization, to orthogonal CP waves at the two nonadjacent frequency bands, e.g., left-handed CP at lower band and right-handed CP at higher band. The polarizer is tested both with 20 and 30 GHz LP rectangular horns to illuminate a dual-band transmit array (TA) to obtain wide-angle steering of CP beams. The performance of the polarizer and its association with the TA is evaluated through simulation and measurements. We also present design guidelines for this type of polarizer. Index Terms— Antenna–filter–antenna, circular polarization (CP), dual-band antennas, frequency selective surfaces, periodic structures, polarization conversion.
Surface plasmons polaritons are collective excitations of an electron gas that occur at an interf... more Surface plasmons polaritons are collective excitations of an electron gas that occur at an interface between negative-ε and positive-ε media. Here, we report the experimental observation of such surface waves using simple waveguide metamaterials filled only with available positive-ε media at microwave frequencies. In contrast to optical designs, in our setup the propagation length of the surface plasmons can be rather long as low loss conventional dielectrics are chosen to avoid typical losses from negative-ε media. Plasmonic phenomena have potential applications in enhancing light– matter interactions, implementing nanoscale photonic circuits and integrated photonics.
In this paper, we propose a ball grid array (BGA) module with an integrated 3-D-printed plastic l... more In this paper, we propose a ball grid array (BGA) module with an integrated 3-D-printed plastic lens antenna for application in a dedicated 130 GHz OOK transceiver that targets the area of 5G backhaul/fronthaul systems. The main design goal was the full integration of a small footprint antenna with an energy-efficient transceiver. The antenna system must be compact and cost effective while delivering an approximately 30 dBi gain in the working band, defined as 120 to 140 GHz. Accordingly, a 2 × 2 array of aperture-coupled patch antennas was designed in the 7 × 7 × 0.362 mm 3 BGA module as the feed antenna of the lens. This achieved a 7.8 dBi realized gain, broadside polarization purity above 20 dB, and over 55% total efficiency from 110 to 140 GHz (20% bandwidth). A plastic elliptical lens 40 mm in diameter and 42.3 mm in height was placed on top of the BGA module. The antenna achieved a return loss better than −10 dB and a 28 dBi realized gain from 114 to 140 GHz. Finally, active measurements demonstrated a >12 Gbps Tx/Rx link at 5 m with bit error rate (BER) < 10 −6 at 1.6 pJ/b/m. These results pave the way for future cost-effective, energy-efficient, high-data rate backhaul/fronthaul systems for 5G communications. Index Terms— 3-D printing, 5G, backhaul/fronthaul links, ball grid array (BGA), dielectric lens, millimeter-wave (mmw) antennas, organic module.
Transmit array design is more challenging for dual-band operation than for single band, due to th... more Transmit array design is more challenging for dual-band operation than for single band, due to the independent 360° phase wrapping jumps needed at each band when large electrical length compensation is involved. This happens when aiming at large gains, typically above 25 dBi with beam scanning and F/ D ≤ 1. No such designs have been reported in the literature. A general method is presented here to reduce the complexity of dual-band transmit array design, valid for arbitrarily large phase error compensation and any band ratio, using a finite number of different unit cells. The procedure is demonstrated for two offset transmit array implementations operating in circular polarization at 20 GHz(Rx) and 30 GHz(Tx) for Ka-band satellite-on-the-move terminals with mechanical beam-steering. An appropriate set of 30 dual-band unit cells is developed with transmission coefficient greater than −0.9 dB. The full-size transmit array is characterized by full-wave simulation enabling elevation beam scanning over 0°−50° with gains reaching 26 dBi at 20 GHz and 29 dBi at 30 GHz. A smaller prototype was fabricated and measured, showing a measured gain of 24 dBi at 20 GHz and 27 dBi at 30 GHz. In both cases, the beam pointing direction is coincident over the two frequency bands, and thus confirming the proposed design procedure.
This paper illustrates the role of additive manufacturing (AM) as enabling technology to realize ... more This paper illustrates the role of additive manufacturing (AM) as enabling technology to realize high-performance low-cost antennas for Ka-band applications. In addition to the inherent electromagnetic challenges implicit in the conception of such complex devices, this paper also points out the stringent limitations that appear when opting for classical fabrication techniques, based on assembled split-block models. AM emerges in this context as a change of paradigm, allowing mono-lithic fabrication and design freedom, which result in substantial improvements in terms of compactness, mass, simplicity, cost, and production time. Two different antennas for Ka-band satellite communications are presented here, namely a wideband horn and a dual-band circular cavity. Both prototypes are fabricated using a stereolithographic (SLA) AM process followed by metal coating. This fabrication approach is especially well suited to the implementation of these designs, since they have internal shapes that are inaccessible to conventional machining tools. The experimental results are not only in very good agreement with the theoretical predictions but also demonstrate improvements over the performances achieved by traditional milling and assembly fabrication approaches, thereby confirming the validity and great potential of SLA for Ka-band satellite communications.
A shaped double-shell dielectric lens is evaluated as a primary feed for a multibeam single-refle... more A shaped double-shell dielectric lens is evaluated as a primary feed for a multibeam single-reflector system operating in the satellite uplink and downlink Ka-bands, complying with gain and edge-of-coverage (EoC) directivity requirements. An assembly of dual-band printed feeds is integrated at the base of a single lens, each feed producing a virtual focus far behind the lens base and coincident with the reflector focal arch. The used double-shell lens approach, instead of a single-material lens, allows an extra degree of freedom to accommodate an aberration mitigation condition. This primary feed system is proposed as a low-complexity solution to enable fitting more beams per solid angle than conventional single-feed-per-beam systems based on a cluster of focal-plane horns. A proof-of-concept lens prototype with 87 mm diameter and 62 mm height, fed by a linear arrangement of five dual-band printed feeds, was fabricated and tested at the Ka-band. The lens measured radiation patterns were post-processed to evaluate the combined performance of the lens with an offset F/D 1 reflector system designed for 45-dBi EoC directivity. It is shown that it duplicates the reflector aperture efficiency compared to horn-fed systems with same feed separation. Index Terms—Dual-band antenna, multibeam antennas, reflector antennas, shaped double shell-lens antenna.
We successfully assess the feasibility of a passive body-implantable sensor antenna concept to re... more We successfully assess the feasibility of a passive body-implantable sensor antenna concept to reach 750 Mbps using impulse radio (IR) in the near-field. It is based on a uniplanar printed antenna configuration, operating in the 1.4-to 4.2-GHz band. The analysis includes the effect of the implant media, the performance in terms of data rate transmission (theoretical and experimental) and feasibility of a " passive " sensor concept in terms of power constraints associated with specific absorption rate (SAR) limits, Federal Communications Commission (FCC) power mask, energy scavenging circuit minimum activation energy, and signal-to-noise ratio (SNR). Finally, we prove the potential of the overall system integrated with an electronic chip model and bio-compatible material. To our knowledge there is no explicit study in the literature that fully demonstrates an implantable system with this kind of data rates addressing all the above. Index Terms—Body-area communication, high data rates, impulse radio (IR), link power budget, passive antenna, phantom, pulse fidelity, specific absorption rate (SAR).
A ball grid array-module (BGA-module) incorporating a low-cost shaped dielectric lens is proposed... more A ball grid array-module (BGA-module) incorporating a low-cost shaped dielectric lens is proposed for wireless communications in the 60-GHz WiGig band between a smart eye-wear, where it is integrated and facing a laptop or TV. The module, which is codesigned with a 60-GHz transceiver, consists of two separate identical antennas for transmitting (Tx) and receiving (Rx). The in-plane separation of these elements is 6.9 mm both being offset from the lens focus. This poses a challenge to the lens design to ensure coincident beam pointing directions for Rx and Tx. The shaped lens is further required to narrow the angular coverage in the elevation plane and broaden it in the horizontal plane. A 3-D-printed eyewear frame with an integrated lens and a recess for proper BGA-module integration is fabricated in ABS-plastic material. Measurements show a reflection coefficient below −12 dB in the 57–66 GHz band. A maximum gain of 11 dBi is obtained at 60 GHz, with 24 • and 96 • beamwidth at 5-dBi gain, respectively, in the vertical and horizontal planes. The radiation exposure is evaluated for a homogeneous SAM head phantom and a heterogeneous visible human head. The simulated power density values for both models are found to be lower than the existing standards.
A simple mechanical beam steering antenna concept is proposed for ground mobile terminals of Ka-b... more A simple mechanical beam steering antenna concept is proposed for ground mobile terminals of Ka-band satellite and high altitude platform (HAP) providing broadband access services. The wide-angle elevation beam steering is achieved by in-plane translation of a thin offset flat lens in front of a stationary primary feed while full azimuth coverage is obtained by simple 360º rotation of the lens. A new strategy is also proposed to reduce the effective F/D of the focusing system and consequently the total antenna height without increasing beam distortion: a second small flat lens is added on top of the primary feed to create a virtual focus located well below the feed phase center. The challenge is to conciliate high gain both with wide beam scanning and reduced antenna height. Design rules are presented for this antenna concept along with a 27.3-dBi gain fabricated example for the up-link Ka-band (29.5–30 GHz), with circular polarization, 0◦ to 50◦ 20 elevation scan, better than 2.8-dB scan loss and an effective F/D of only 0.55. Both lenses are 3.35-mm thick, formed by a suitable assembly of phase shifting unit cells with less than 0.4 dB of transmission loss in simulation. The main lens dimensions are 195 mm × 145 mm and its weight is 215 g. Total antenna height, including the feed is 26 84 mm.
The design of a micromachined polyethylene lens for WiGig modules is described and its electromag... more The design of a micromachined polyethylene lens for WiGig modules is described and its electromagnetic characteristics are measured. The lens is electromagnetically fed by linearly polarized Tx and Rx patch antennas integrated in an existing ball-grid-array (BGA) organic module. Antennas are separated from each other by a distance of 4.45 mm (0.89lambda at 60 GHz). The goal of the lens is to increase the gain of each antenna while lowering the beam depointing effect due to their offset position regarding the focal point of the lens. A geometrical optics/physical optics (GO/PO) hybrid method is applied to the design and analysis of the lens shape for noncollimating purpose. Using a lens height of 30 mm for both Tx and Rx antennas, a 13-dBi minimum realized gain from 54 to 66 GHz is obtained. Compared to an elliptical lens providing an equivalent realized gain over the same bandwidth, the depointing angle from the boresight direction is reduced from 15° to 4°. Full-wave simulations are verified by measurements.
A complete UHF radio-frequency identification (RFID)-based system capable of localizing individua... more A complete UHF radio-frequency identification (RFID)-based system capable of localizing individual blood bags inside storage cabinet drawers is presented. It was developed to demonstrate the improvement possibility of current blood stock management systems and as the submission to the 2014 IEEE AP-S Student Design Contest: Antennas for RFID Application. The system is composed of a cabinet model, a transceiver unit, and a PC with the controlling software. A new implementation of pseudolocalization principle is used to localize the blood bags that are equipped with dedicated passive tags designed to be resilient to blood proximity and small size. The detector antennas are placed at the drawers bottoms and additional passive tags are utilized to identify individual locations in each drawer. The transceiver unit is made from off-the-shelf commercial electronic boards and wirelessly controlled by software run on the PC. The entire system is small, transportable, battery powered, and low cost.
A simple low-cost mobile ground terminal antenna for Ka-band satellite communications is presente... more A simple low-cost mobile ground terminal antenna for Ka-band satellite communications is presented. The antenna is composed of a shaped dielectric lens which tilts and rotates in front of a feed to direct the beam. The wideband feed system is composed of a quad-ridged horn with a 45° slant aperture and a coaxial-to-quad-ridged circular waveguide transition. The lens allows simple mechanical beam steering from 0° to 65° in relation to the zenith and 360° in azimuth by rotating both the lens and the feed slanted aperture. Performance measurements of a manufactured prototype prove the beam tilting capabilities in elevation with a maximum gain of 22 dBi and scan loss below 3 dB at 20 GHz and 24 dBi gain with less than 4.5 dB scan loss at 30 GHz.
Starting from a challenge in the early 1990s to develop a highly shaped beam dielectric lens ante... more Starting from a challenge in the early 1990s to develop a highly shaped beam dielectric lens antenna for a pilot 150 Mb/s cellular mobile broadband system operating in the 60-GHz band, several new developments have been accomplished over more than 20 years at Instituto de Telecomunicações [1] in the areas of millimeter-wave shaped dielectric lens antennas and planar metamaterial lenses. We review here a few representative examples with numerical and experimental results, covering applications in mobile broadband communications, radiometry, satellite communications, multigigabit short-range communications, and sublambda near-field target detection.
Dielectric lens antennas are proposed for wireless broadband communication systems in the mm-wave... more Dielectric lens antennas are proposed for wireless broadband communication systems in the mm-wave range. Two lens antenna configurations for base station applications are presented and evaluated in terms of radiation characteristics, feeding system, input reflection loss, bandwidth and fabrication tolerances. The system requirements to provide optimum power distribution over the cell and good control of the cell boundaries are achieved.
European Conference on Antennas and Propagation, Mar 23, 2009
Abstract This paper presents a simple yet very effective antenna solution for confined RFID detec... more Abstract This paper presents a simple yet very effective antenna solution for confined RFID detection within the limits of a bookshelf, operating at the three world assigned RFID sub-bands at UHF. The proposed concept uses a leaking microstrip transmission line with extended ground plane embedded on the shelf. When associated to a RFID reader, the proposed solution, allows univocal detection of tagged books above the shelf with proper field confinement to avoid undesired reading of neighboring shelves. The concept is ...
UWB technology is a promising candidate for Body Area Network (BAN) applications, especially in r... more UWB technology is a promising candidate for Body Area Network (BAN) applications, especially in radar and localization due to superior ranging capabilities in comparison to narrowband systems like RFID, and Wi-Fi. Centimeter precision is expected when using IR-UWB (Impulse Radio UWB) in ranging and localization, and given that the antennas have a crucial role in forming the radiated pulse, special attention has to be given to their design. Good IR-UWB BAN antenna should present following characteristics both in free-space and when placed in close body proximity: stable impedance and radiation pattern in the band, flat transfer function amplitude versus frequency, high value of impulse fidelity, and high radiation efficiency. In terms of physical characteristics the antenna should be small and low profile in order to be easily blended with user's clothing or taped to the skin. To the best of authors' knowledge there is no UWB antenna in the literature that satisfies all of mentioned conditions simultaneously. Therefore we will present here a stacked, two-layer UWB antenna that demonstrates high resistance to body proximity and satisfies all before mentioned characteristics.
European Conference on Antennas and Propagation, May 13, 2015
This paper presents a modified methodology to compute the phase center of planar antennas. It is ... more This paper presents a modified methodology to compute the phase center of planar antennas. It is especially well suited for low-profile geometries without axial symmetry that are currently being proposed as feeder systems for Ka-band lens antennas. By taking into account new features, such as large spherical surface consideration and dual electric field components, this modified algorithm results in improved designs for complete Ka-band, lens-based systems showing consistently an enhanced gain.
A low profile unidirectional UWB antenna for WBAN (Wireless Body Area Networks) Impulse Radio (IR... more A low profile unidirectional UWB antenna for WBAN (Wireless Body Area Networks) Impulse Radio (IR) applications is proposed with functional band from 7 GHz to 10.7 GHz. Simulated reflection coefficient in free space and when 0 mm, 3 mm, or 7 mm above a human body model show that the body influence is minimal. Time domain study of pulse fidelity, of crucial importance for IR-UWB, shows average fidelity of 98% in free space and when 3 mm or 0 mm above the body.
European Conference on Antennas and Propagation, May 13, 2015
A new multibeam antenna for imaging based on planar lenses working at the frequency of 10 GHz is ... more A new multibeam antenna for imaging based on planar lenses working at the frequency of 10 GHz is presented in this communication. Firstly, a new planar lens for a phase-correcting application is designed using an ideal feed, so the feed placed in the focus generates a broadside beam. This lens is used to find the final positions of the different feeds of the network, so the crossover between adjacent beams is at 3dB below the maximum. Moreover, a quasi-yagi antenna is designed to match the behavior of the ideal one used in the initial process. In this case, it is necessary to assure that its behavior is stable when placed within a complex network. Finally, with the results of each of the antennas, the final behavior of the system is analyzed.
Abstract Reconfigurable antennas are very attractive since they enable to electronically change i... more Abstract Reconfigurable antennas are very attractive since they enable to electronically change its operating frequency, polarization or radiation patterns. GaAs FET and PIN diodes or, more recently, RF MEMS are widely used to perform the required switching operations. The advantages of MEMS switches, when compared to diodes, are the higher isolation, better linearity, lower insertion loss, near-zero power consumption and operation over a wider frequency range. To validate the referred modeling, a compact reconfigurable ...
Cosecant squared cell illumination may contribute to enhance system performance in MM-wave wirele... more Cosecant squared cell illumination may contribute to enhance system performance in MM-wave wireless communication systems. Previously proposed axial symmetric dielectric lens antennas produce a most useful constant flux circular footprint, but they fail to cover the regions near the vertices of square cells. This paper presents a simplified procedure to design a 3D dielectric lens that produces a constant-flux square foot print, intended for the illumination of square or rectangular cells. Calculated and measured antenna performance is presented not only in terms of radiation pattern, but also in terms of coverage, and time dispersion.
Wildfires are a recurring phenomenon in many countries around the world, either due to natural ca... more Wildfires are a recurring phenomenon in many countries around the world, either due to natural causes or negligent human behavior. Emergency communication services used by firefighters at the theater of operations must be highly reliable, in order to ensure the safety and coordination of the teams that are fighting the wildfire, contributing to extinguishing it as quickly as possible with minimum use of resources. Emergency communication networks strongly rely on wireless links that may be impaired by the flames. In this work, we present an experimental setup for characterization of fire at microwave frequencies. Preliminary results show that we are able to extract very low dielectric constant (<1.1) using ultrawideband signals. Moreover, we characterize the attenuation introduced by fire in small-scale scenario. Future work will include the characterization of fire in larger-scale scenarios.
2021 15th European Conference on Antennas and Propagation (EuCAP), 2021
Microwave Imaging (MWI) has the potential to aid breast cancer staging through the detection of A... more Microwave Imaging (MWI) has the potential to aid breast cancer staging through the detection of Axillary Lymph Nodes (ALNs). This type of system can present some challenges, mainly due to the irregular axillary surface. The optimisation of the artefact removal algorithm to successfully remove the surface reflections is of great importance. In this paper, we propose using Singular Value Decomposition (SVD) as an artefact removal algorithm and study the effect of choosing different subsets of antenna positions for artefact removal on imaging results using experimental signals. We show that different subsets of antenna positions affect the results and in some cases prevent the targets detection. Our analysis allowed us to find an optimal combination of parameters which results in Signal-to-Clutter Ratio higher than 2.77 dB and Location Error lower than 14.9 mm for three different experimental tests. These results are relevant for the development of dedicated algorithms for ALN-MWI application.
IEEE Antennas and Propagation Society Symposium, 2004., 2004
Jorge R. Costa*, Carlos A. Femandes Instituto de Telecomunicapjes, Instituto Superior TCcnico, AV... more Jorge R. Costa*, Carlos A. Femandes Instituto de Telecomunicapjes, Instituto Superior TCcnico, AV. Rovisco Pais 1049-001 Lisboa, Portugal. E-mail: Jorec.Costn(iiilx.i(.D1, Carlos.Fcmaridcs~~Ix.it.pt ... ABSTRACT A Gabor variant is presented to determine the near-field from axial symmetric feeds with $-independent fields. This method can be used for the analysis of small shaped dielectric lens antennas, when the classical Geometric Optics based approach fails. lNTRODUCTlON Integrated Lens Antennas (ILA) have been used for ...
2021 15th European Conference on Antennas and Propagation (EuCAP), 2021
In this paper, a range of refractive indexes found in simulations of fire scenarios, considering ... more In this paper, a range of refractive indexes found in simulations of fire scenarios, considering the Cold Plasma Model, is explored. The Fire Dynamics Simulator (FDS) was used to model a Pinus Pinaster fuel bed burning in a linear burner. The effects of maximum and minimum refractive index values were analysed using the Finite-Difference Time-Domain (FDTD) method, aiming to understand how electric characteristics of a plasma may affect the electromagnetic wave propagation. Results clearly indicate the need to further investigate the propagation phenomena under wildfire conditions.
Satellite connectivity is a well-established system to provide wireless connectivity to peers tha... more Satellite connectivity is a well-established system to provide wireless connectivity to peers that are either in a remote location or which have a high mobility and cannot use a fixed datalink. The authors have designed a wide-band circular horn antenna that covers the frequency band from 19.7 to 30 GHz, including simultaneously the down-link and up-link bands of satellite communication in Ka-band. Wide-band behavior for both linear modes of the circular waveguide is achieved using 4 ridges symmetrically placed; and a small back-cavity near the input coaxial port is used to improve and fine-tune the return losses of the antenna. An additional degree of freedom is achieved by introducing a tuning pin in the cylindrical waveguide. The position of this tuning pin allows fine-tuning the prototype once manufactured. Due to the complexity of the antenna, its fabrication using standard milling techniques is challenging, as previously presented by the authors, and requires a split-block app...
Aperture Antennas for Millimeter and Sub-Millimeter Wave Applications, 2017
This chapter presents the Integrated Lens Antenna (ILA) technology as it evolved since its introd... more This chapter presents the Integrated Lens Antenna (ILA) technology as it evolved since its introduction aiming to respond to the needs of emerging applications such as high-data-rate communication, intelligent transport, and mm-wave imaging. The topics covered include the ILA design concepts as well as the electromagnetic phenomena intrinsic to dielectric lenses that may affect ILA performance. The aspects of the ILA technology related to selection of the primary feeds, lens materials, and fabrication methods are also revised. A few practical examples are provided to illustrate the current and future trends of this technology.
Dielectric lens antennas are attracting a renewed interest for millimetre-and sub-millimetre wave... more Dielectric lens antennas are attracting a renewed interest for millimetre-and sub-millimetre wave applications where they become compact, especially for configurations with integrated feeds usually referred as integrated lens antennas. Lenses are very flexible and simple to design and fabricate, being a reliable alternative at these frequencies to reflector antennas. Lens target output can range from a simple collimated beam (increasing the feed directivity) to more complex multi-objective specifications. This chapter presents a review of different types of dielectric lens antennas and lens design methods. Representative lens antenna design examples are described in detail, with emphasis on homogeneous integrated lenses. A review of the different lens analysis methods is performed, followed by the discuss ion of relevant lens antenna implementation issues like feeding options, dielectric material characteristics, fabrication methods and a few dedicated measurement techniques. The chapter ends with a detailed presentation of some recent application examples involving dielectric lens antennas.
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Journal Papers by Carlos A Fernandes