116 research outputs found

    Beam scanning by liquid-crystal biasing in a modified SIW structure

    Get PDF
    A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

    1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

    Get PDF
    A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

    ECOS 2012

    Get PDF
    The 8-volume set contains the Proceedings of the 25th ECOS 2012 International Conference, Perugia, Italy, June 26th to June 29th, 2012. ECOS is an acronym for Efficiency, Cost, Optimization and Simulation (of energy conversion systems and processes), summarizing the topics covered in ECOS: Thermodynamics, Heat and Mass Transfer, Exergy and Second Law Analysis, Process Integration and Heat Exchanger Networks, Fluid Dynamics and Power Plant Components, Fuel Cells, Simulation of Energy Conversion Systems, Renewable Energies, Thermo-Economic Analysis and Optimisation, Combustion, Chemical Reactors, Carbon Capture and Sequestration, Building/Urban/Complex Energy Systems, Water Desalination and Use of Water Resources, Energy Systems- Environmental and Sustainability Issues, System Operation/ Control/Diagnosis and Prognosis, Industrial Ecology

    Analysis of Substrate Integrated Waveguides

    Get PDF
    By using a transverse resonance technique, the frequency characteristics of slotted substrate integrated waveguides (SSIWs), slotted half mode substrate integrated waveguides (slotted HMSIWs) and slotted parallel plate SIWs loaded with capacitances and inductances are analyzed theoretically and related to those of conventional waveguides. In practice, the slotted SIWs and HMSIWs are distributed structures, so that they are loaded with ladders of capacitances and inductances across their slots. The cut-off frequencies of the slotted SIWs and HMSIWs loaded with specific capacitances and inductances are then calculated from our analytic technique. These numerical predictions are both compared with and also in some cases used to clarify the corresponding values of cut-off frequencies estimated by HFSS and also by CST Microwave Studio by means of using S-parameters. Field plots for some of these practical examples are used to provided further insights regarding the design and operation of these structures. A tuneable resonator and tuneable single port narrow band antenna are designed. A rudimentary design of a bandpass filter (in the form of a SIW loaded with both inductances and capacitances in series across the slot) is also outlined. Finally, a modal analysis technique for a general composite waveguide structure, essentially consisting of three sections of SIW, is developed from first principles. This method is used to establish matrices which are used to calculate the S-parameters of the full structure. Though the technique itself is not entirely original, its application is a novel one which can be applied to a whole range of hybrid waveguide structures. Some specific examples of the general case which have practical importance, namely rectangular SIW sections at either end of a slotted SIW region via means of a step with E-planes and H-planes respectively, are considered. The operational characteristics of these waveguide structures are analyzed by means of examining their S-parameters over a suitable range of frequencies. These predicitions are then compared with, and also in some cases, used to interpret the S-parameter estimates from HFSS. The calculated predictions from the modal analysis for these examples are useful for the determination of frequency characteristics of SSIWs, which are instrumental in the novel design of a plethora of microwave devices. In fact, the mode matching method is compared with CST Microwave Studio to estimate the cutoff frequency of a slot SIW antenna

    Lumped silicon photonic Mach-Zehnder modulators for high-speed optical interconnects

    Get PDF
    The boom in worldwide internet connectivity and cloud services has caused unprecedented need for high-bandwidth connections between and within data centres. Silicon photonics is becoming the platform of choice to provide low-cost, large-volume production of future optical transceivers. However, the scale of modern data centres introduces challenges of speed, reach and, crucially, energy consumption for these devices. Silicon photonic Mach-Zehnder modulators (MZMs) are one possibility for providing electrical-to-optical conversion at the transmit side of such fibre-optic links. In this thesis, comprehensive investigation is carried out into lumped MZMs, specifically, as their unterminated, capacitive load holds promise for lower power consumption than more typical travelling-wave MZMs with resistive terminations. Detailed characterisations and simulations of dual-drive silicon photonic lumped MZMs are made to investigate the key trade-off of modulation bandwidth and drive voltage. Drivers with low source impedance are investigated as a means of boosting lumped MZM bandwidths, while advanced modulation formats such as four-level pulse-amplitude modulation (PAM4) and electrical duobinary modulation (EDB) are also leveraged to provide more spectrally-efficient signals. In particular, experimental demonstration is made of a novel low-impedance, switched-capacitor PAM4 driver for a lumped MZM in a 30 Gb/s silicon photonic link over 10 km of optical fibre. Simulations are carried out to optimise the bias and doping levels of lumped MZMs used with such drivers. Predistortion methods are investigated through experiments and simulations as alternative ways to increase the bandwidth. A simple first-order FIR filter is shown experimentally to enable 25 Gb/s NRZ modulation with a low-bandwidth MZM, while more optimised precompensation enables 50 Gb/s PAM4 and EDB. Finally, simulations using an accurate equivalent circuit model for the lumped MZM demonstrate the potential for a well-designed driver with lowered source impedance and controlled amounts of inductive peaking to reduce the need for transmitter-side precompensation
    • …
    corecore