2008/2

Browse

Recent Submissions

Now showing 1 - 5 of 22
  • Thumbnail Image
    Item
    Fiber-Optic Vibration Sensor Based on Multimode Fiber
    (Společnost pro radioelektronické inženýrství, 2008-06) Lujo, Ivan; Klokoc, Pavo; Komljenovic, Tin; Bosiljevac, Marko; Sipus, Zvonimir
    The purpose of this paper is to present a fiberoptic vibration sensor based on the monitoring of the mode distribution in a multimode optical fiber. Detection of vibrations and their parameters is possible through observation of the output speckle pattern from the multimode optical fiber. A working experimental model has been built in which all used components are widely available and cheap: a CCD camera (a simple web-cam), a multimode laser in visible range as a light source, a length of multimode optical fiber, and a computer for signal processing. Measurements have shown good agreement with the actual frequency of vibrations, and promising results were achieved with the amplitude measurements although they require some adaptation of the experimental model. Proposed sensor is cheap and lightweight and therefore presents an interesting alternative for monitoring large smart structures.
  • Thumbnail Image
    Item
    Broadband SHF Direction-Finder
    (Společnost pro radioelektronické inženýrství, 2008-06) Radionov, Sergey; Ivanchenko, Igor; Korolev, Alexey; Popenko, Nina
    The original design of the compact broadband direction-finder is presented in this paper. The cylindrical monopole antenna serves as a primary source of the reflector- type antenna. \"Zero-amplitude\" technique is used for bearing the SHF sources. The model experiments with the proposed direction-finder prototype in the frequency band 6 GHz – 11 GHz have been carried out.
  • Thumbnail Image
    Item
    Analysis of Highly Directive Cavity-Type Configurations Comprising of Low Profile Antennas Covered by Superstrates
    (Společnost pro radioelektronické inženýrství, 2008-06) Farahat, Nader; Mittra, Raj; Lugo, Katherine; Ma, Lai-Ching; Gomez, Rodney A.
    In this paper we present a technique for designing antenna/superstrate composites to produce enhanced directivities. As a first step, we study the underlying mechanism that governs the performance of theses antennas by studying the canonical problem of a line source in a rectangular waveguide. The above problem is solved by constructing the Green’s function corresponding to the line source in the rectangular guide, one of whose walls is partially reflecting, that is can leak electromagnetic energy into the space external to the guide. The Green’s function for this problem can be constructed by aggregating the multiple reflections from the two walls. Although the above model is only two-dimensional, we show that it can be used to predict the performance of antenna/superstrate composites. We demonstrate this by modeling several highly directive antennas and show that indeed the required characteristics of this type of antennas can be determined from the analysis of the cutoff behavior of the rectangular guide.
  • Thumbnail Image
    Item
    Local Positioning Services on IEEE 802.11 Networks
    (Společnost pro radioelektronické inženýrství, 2008-06) Vegni, Anna Maria; Di Nepi, Alessandro; Neri, Alessandro; Vegni, Claudio
    This paper deals with localization services in IEEE 802.11 networks, for indoor environment. The proposed solution processes the Time Of Arrival of location packets sent by a Mobile Terminal, that makes access in a IEEE 802.11 network. A set of Location Supporting Nodes and a Location Support Server composes an indoor location services architecture. A fully compatible IEEE 802.11 Localization Services protocol supporting data exchange related to both TOA measurement and processing is reported. Simulation results show the method efficiency in both IEEE 802.11 PCF and DCF modes. Assessment of the maximum number of users for which location services can be provided is also reported. Since high localization accuracy requires large bandwidth, a broadband antenna for LSN and LSS was designed. The related results are reported in the second part of the paper. The antenna works at 5.0 GHz (centre frequency) in broadband mode and is matched on the wireless operating frequencies with a percentage more than 8% (1:1.5 VSWR).
  • Thumbnail Image
    Item
    Enhanced Coupling Values in Coupled Microstrip Lines using Metamaterials
    (Společnost pro radioelektronické inženýrství, 2008-06) Lauro, Sebastian E.; Toscano, Alessandro; Vegni, Lucio
    In this paper, we show how metamaterials can be used to enhance the coupling values of microstrip directional couplers. Coupling between regular coplanar microstrip lines, in fact, is limited, due to the small ratios between the characteristic impedances of even and odd TEM modes supported by the structure. The broadside configuration or the employment of an overlay are often utilized to overcome this limitation, leading, however, to more bulky components. On the other hand, the employment of metamaterials with a negative real part of the permittivity is able to increase the coupling values, while keeping the profile of the structure very low. A quasi-static model of the structure is developed and physical insights on the operation of the proposed component and on the role of the metamaterial loading are also given. Simple design formulae derived through a conformal mapping technique are presented and validated through proper full wave numerical simulations.