Percorrer por autor "Reis, João R."
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- Compact 3D‐printed reflector antenna for radar applications at K‐bandPublication . Reis, João R.; Ribeiro, Carlos; Caldeirinha, Rafael F. S.A compact parabolic reflector antenna aiming at radar applications in the K-band is presented. It is mainly composed of a thermoplastic material and using classical additive techniques (also known as 3D printing), the proposed high-gain antenna exhibits a novel and unique form factor, particularly of interest for applications with low payload capacity, for example unmanned aerial vehicles. The antenna is composed of four parts: (i) a paraboloid shape embodied in a supporting polylactic acid (PLA) material; (ii) a metallic coating applied to the paraboloid surface of (i), to enable it with electromagnetic reflecting properties; (iii) a PLA spacer that ensures the physical separation (i.e. focal distance) between parts (i) and (iv) and, finally, (iv) a microstrip patch antenna with a reduced ground plane to reduce feed blockage. Subsequently to an overview on the theoretical formulation of parabolic reflector antennas, an antenna targeting 20 dBi and a minimum bandwidth of 500 MHz operating in the 24 GHz ISM radar band have been dimensioned, optimised in CST Microwave Studio and validated against measurements performed on a physical prototype. The simulation and experimental results are in good agreement with the prototype yielding 18.3 dBi of gain and 2.2 GHz of useful bandwidth, clearly demonstrating the potential of the proposed antenna design.
- Electronically Reconfigurable FSS-Inspired Transmitarray for 2-D BeamsteeringPublication . Reis, João R.; Caldeirinha, Rafael F. S.; Hammoudeh, Akram; Copner, NigelA novel electronically reconfigurable transmitarray (TA) with 2-D beamsteering capability is presented in this communication. The proposed structure, inspired on frequency selective surfaces loaded with varactor diodes, allows the phase range of each TA element to be individually controlled enabling an automated steering of the main lobe of an original antenna pattern, in both elevation and azimuth planes (2-D beamsteering). This has been demonstrated on a 5 × 5 unit-cell stacked structure with active feeding, coupled to the aperture of a standard gain horn antenna. A complete electromagnetic study using CST Microwave Studio is presented to evaluate and characterize the TA elements and the effect the proposed feeding network has on the structure's behavior. Following initial simulations, a prototype of the active TA has been characterized. Automated antenna beamsteering with ranges up to Az = 28° and El = 26° and 1° of angular resolution, is achieved by means of electromagnetic simulations and validated against experimental results at 5.2 GHz.
- High Performance Antennas for Early Fire Detection Wireless Sensor Networks at 2.4 GHzPublication . Oliveira, Tiago E. S.; Reis, João R.; Vala, Mário; Caldeirinha, Rafael F. S.In this paper, high performance antennas are pro-posed for massive deployment of wireless sensor networks (WSN) for early fire dectection in forested areas. A differential slotted microstrip patch antenna and a Quasi-Yagi microstrip antenna are proposed to be implemented in a WSN at 2.4 GHz (ISM band). Firstly, a microstrip Quasi-Yagi antenna has been studied and optimised to operate at 2.4 GHz, which is sough to be deployed as part of a sectorized base-station. The antenna is comprised of one reflector and six directors around a microstrip patch to create an end-fire radiation pattern. According to simulations, the optimised antenna reaches a gain of 9.41 dBi and a half-power beamwidth of 70° at 2.44 GHz, with a operating frequency band from 2.27 to 2.83 GHz. For the sensor node, a very small differential slotted microstrip patch antenna is proposed, which has been redesigned and optimised to operate at 2.4 GHz. The proposed design takes advantage of slotted resonant elements in order to reduce the overall size of the antenna. Simulation results ensure a realised gain of 4.15 dBi at 2.44 GHz and an operating frequency band from 2.37 to 2.5 GHz. The results present in this paper were performed by using the simulation software CST-MWS.
- Metamaterial-inspired Flat-Antenna Design for 5G Small-cell Base-Stations Operating at 3.6 GHzPublication . Reis, João R.; Fernandes, Telmo R.; Patrício Carreira Vala, Mário António; Caldeirinha, Rafael F. S.In this paper, a flat-beamsteering antenna for 5G applications is being presented. The antenna, designed to operate at 3.6 GHz (5G new radio (NR) frequency range 1 (FR1) band n78), presents a unique flat form factor which allows easy deployment and low visual impact in 5G dense scenarios. The antenna presents a multi-layer structure where a metamaterial inspired transmitarray enables the two-dimensional (2D) beamsteering, and an array of microstrip patch antennas is utilised as RF source. The use of metamaterials for beamsteering control allows for the reduction of costly and complex phase-shifter networks by using discrete capacitor diodes to control the transmission phase-shifting and subsequently, the direction of the steering. According to simulations, the proposed antenna presents 13.9 dBi of gain, 100 MHz of bandwidth with a maximum steering range of ±20 degrees, achievable in both elevation and azimuth planes, independently.
- STDCC radar at 24 GHz: first measurement trialsPublication . Ferreira Sardo, Andre; Reis, João R.; Duarte, Luis; Leonor, Nuno; Ribeiro, Carlos; Caldeirinha, Rafael F. S.This paper presents the first measurement trials for performance assessment of a real-time and high resolution monostatic radar operating at 24 GHz. The proposed real-time radar, which operates based on the sliding correlation of pseudo-noise (PN) sequences, provides a high time resolution better than 4 ns, useful for moving target identification (MTI) in the presence of highly dense clutter, under harsh environments and severe weather conditions (fog, snow and fire smoke or plume). The STDCC radar target detection capability is demonstrated in this paper, by measuring and identifying the radar data for 4 distinct scenarios, composed of multiple targets (up to 8), inside an anechoic chamber, demonstrating the potential of the proposed radar architecture.