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Browsing CTM by Author "296"
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    5.36 Gbit/s OFDM optical wireless communication link over the underwater channel
    ( 2020) João Henrique Araújo ; Luís Manuel Pessoa ; Henrique Salgado ; Pereira,F ; Joana Santos Tavares ; Kraemer,R ; 7658 ; 4760 ; 296 ; 5686
    An OFDM transmission system is reported based on a directly modulated blue LASER diode, for high bit rate under-water optical communication applications. The 256 subcarriers 16-QAM signal is transmitted over a total distance of 2.4 m underwater with an EVM lower than -28.5 dB for a 250 MHz bandwidth and -16.5 dB for a 2 GHz bandwidth, the BER being lower than the forward error corrector limit. At the maximum bandwidth of 2 GHz a transmission rate of 5.36 Gbit/s is achieved. © 2020 IEEE.
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    Design of an underwater sensor network perpetually powered from AUVs
    ( 2019) Manuel Cândido Santos ; Matos,A ; Cruz,NA ; Ferreira,B ; Correia,V ; Luís Manuel Pessoa ; Henrique Salgado ; 4730 ; 296 ; 4760
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    Elliptical Monopole Antenna on InP Substrate for Sub-THz RTD-based Oscillators
    ( 2018) Henrique Salgado ; Hugo Miguel Santos ; Luís Manuel Pessoa ; Pinho,P ; 296 ; 4760 ; 6335
    The high permittivity of InP substrates has been a limiting factor for the bandwidth and efficiency of antennas fabricated in this material. In this manuscript we propose an elliptical monopole, monolithically fabricated in InP, fed by a CPW line. The suggested topology was simulated using HFSS finite element method. Input reflection coefficient measurements were performed on the monopole to validate the proposed antenna. Simulated and measured -10 dB bandwidths of 27 and 24 GHz were obtained, respectively. The peak simulated efficiency and realized gain were 95.37% and 4.6 dBi.
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    Experimental Evaluation of Resonant Tunnelling Diode Oscillators Employing Advanced Modulation Formats
    ( 2018) Henrique Salgado ; Joana Santos Tavares ; Luís Manuel Pessoa ; 5686 ; 296 ; 4760
    The performance of Resonant Tunnelling Diode (RTD) oscillators with an optical window is evaluated experimentally, in the transmission of advanced modulation formats using electrical and optical modulation, for the first time. Additionally, the impact of phase noise in the transmission performance is also assessed. © 2018 IEEE.
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    A Gaussian Window for Interference Mitigation in Ka-band Digital Beamforming Systems
    ( 2022) Joana Santos Tavares ; Avelar,HH ; Henrique Salgado ; Luís Manuel Pessoa ; 5686 ; 296 ; 4760
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    LASER diode-based transmitter module for optical wireless communications
    ( 2020) Henrique Salgado ; Santos,HM ; Kraemer,R ; João Henrique Araújo ; Luís Manuel Pessoa ; Pereira,F ; 7658 ; 4760 ; 296
    In this paper, we present the design of an analog transmitter based on a blue LD targeting optical wireless communications, suitable for OFDM signals. The approach relies on a thorough characterization of the individual components of the module, whence a detailed circuit model is obtained to design an impedance matching circuit for improved performance, prior to fabrication. The impedance matching is based on non-uniform transmission lines and works well over a wide frequency range (100 MHz to 2 GHz). The results are experimentally validated by the transmitter response exhibiting an increased 6 dB bandwidth limit and 1 GHz bandwidth improvement. © 2020 IEEE.
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    Misalignment-Resilient Propagation Model for Underwater Optical Wireless Links
    ( 2023) João Henrique Araújo ; Joana Santos Tavares ; Marques,VM ; Henrique Salgado ; Luís Manuel Pessoa ; 296 ; 4760 ; 5686 ; 7658
    This paper proposes a multiple-lens receiver scheme to increase the misalignment tolerance of an underwater optical wireless communications link between an autonomous underwater vehicle (AUV) and a sensor plane. An accurate model of photon propagation based on the Monte Carlo simulation is presented which accounts for the lens(es) photon refraction at the sensor interface and angular misalignment between the emitter and receiver. The results show that the ideal divergence of the beam of the emitter is around 15° for a 1 m transmission length, increasing to 22° for a shorter distance of 0.5 m but being independent of the water turbidity. In addition, it is concluded that a seven-lense scheme is approximately three times more tolerant to offset than a single lens. A random forest machine learning algorithm is also assessed for its suitability to estimate the offset and angle of the AUV in relation to the fixed sensor, based on the power distribution of each lens, in real time. The algorithm is able to estimate the offset and angular misalignment with a mean square error of 5 mm (6 mm) and 0.157 rad (0.174 rad) for a distance between the transmitter and receiver of 1 m and 0.5 m, respectively.
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    Optical direct intensity modulation of a 79GHz resonant tunneling diode-photodetector oscillator
    ( 2019) Zhang,WK ; Kelly,AE ; Wasige,E ; Henrique Salgado ; Al Khalidi,A ; Luís Manuel Pessoa ; Joana Santos Tavares ; Cantu,HI ; Wang,J ; Figueiredo,J ; Watson,S ; 296 ; 5686 ; 4760
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    Resonant tunneling diode photodetectors for optical communications
    ( 2019) Watson,S ; Kelly,A ; Luís Manuel Pessoa ; Henrique Salgado ; Wasige,E ; Wang,J ; Cantu,H ; Figueiredo,J ; Joana Santos Tavares ; Zhang,WK ; 4760 ; 296 ; 5686
    Optical modulation characteristics of resonant tunneling diode photodetectors (RTD-PD) are investigated. Intensity modulated light excites the RTD-PDs to conduct data experiments. Simple and complex data patterns are used with results showing data rates up to 80 and 200 Mbit/s, respectively. This is the first demonstration of complex modulation using resonant tunneling diodes. © 2019 The Authors. Microwave and Optical Technology Letters published by Wiley Periodicals, Inc.
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    Scalable High-Gaussicity Split-Block Diagonal Horn Antenna for Integration with Sub-THz Devices
    ( 2019) Erick Delgado Lima ; Henrique Salgado ; Moro Melgar,D ; Luís Manuel Pessoa ; Pinho,P ; Hugo Miguel Santos ; 6335 ; 4760 ; 296 ; 7162
    In this paper we propose a high-gaussicity spline-profiled horn antenna, which is scalable in length and aperture to achieve higher gains whilst retaining a high Gaussian efficiency. A novel approach is used where a PSO is used for optimizing the spline, using the gaussicities at the operating frequencies as the objective function, which further improves side-lobe level and cross-polarization when compared to the state-of-the-art. With the proposed method, which was validated through FEM simulations in HFSS, reflection coefficients below -15 dB, gains greater than 25 dBi and gaussicities above 91% were obtained in the entire WR-3 band.