2008/2

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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.
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).
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.
Terminal Antennas in ACE2
(Společnost pro radioelektronické inženýrství, 2008-06) Martinez-Vazquez, Marta; Serrano, Raquel; Carlsson, Jan; Skrivervik, Anja K.
The ACE Network of Excellence was a European Commission funded Network of Excellence, which lasted from 2004 to 2007. One of the activities performed by this Network was in the frame of terminal antennas. In this activity, three aspects were covered in three projects: Small antenna technologies, small terminal antenna technologies and benchmarking of small terminal antennas measurement facilities. The overall aim was to identify the newest trends in antenna design and measurement for personal communications devices, and suggest novel solutions and design methodologies for various applications. The results of this work are presented in this paper.
Wide-Angle X-Band Antenna Array with Novel Radiating Elements
(Společnost pro radioelektronické inženýrství, 2008-06) Chernobrovkin, Roman; Ivanchenko, Igor; Ligthart, Leo P.; Korolev, Aleksey; Popenko, Nina
An antenna array with wide-angle beam steering is presented in this paper. The antenna consists of dielectrically filled open-ended waveguides with a new type of excitation as individual radiators. The characteristics of the radiator have been analyzed. The novel radiator has a wide beamwidth and the frequency band of around 21%. Following the computational modeling and experimental investigations the characteristics of the antenna array for scan angles up to 50° are discussed.

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