Influence of the Antennas on the Ultra-Wideband Transmission
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Influence of the Antennas on the Ultra-Wideband Transmission ¨ Werner Sorgel Institut f¨ur H¨ochstfrequenztechnik und Elektronik, Universit¨at Karlsruhe (TH), Kaiserstrasse 12, 76128 Karlsruhe, Germany Email: [email protected]
Werner Wiesbeck Institut f¨ur H¨ochstfrequenztechnik und Elektronik, Universit¨at Karlsruhe (TH), Kaiserstrasse 12, 76128 Karlsruhe, Germany Email: [email protected] Received 29 October 2003; Revised 16 February 2004 Spectrum is presently one of the most valuable goods worldwide as the demand is permanently increasing and it can be traded only locally. Since the United States Federal Communications Commission (FCC) has opened the spectrum from 3.1 GHz to 10.6 GHz, that is, a bandwidth of 7.5 GHz, for unlicensed use with up to −41.25 dBm/MHz EIRP, numerous applications in communications and sensor areas are showing up. Like all wireless devices, these have an antenna as an integral part of the air interface. The antennas are modeled as linear time-invariant (LTI) systems with a transfer function. The measurement of the antenna’s frequency-dependent directional transfer function is described. Quality measures for the antennas like the peak value of the transient response, its width and ringing, as well as the transient gain are discussed. The application of these quality measures is shown for measurements of different UWB antennas. Keywords and phrases: ultra-wideband, ultra-wideband antennas, quality measures for UWB antennas, time-domain antenna characterization, transient radiation and reception.
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INTRODUCTION
In April 2002, the Federal Communications Comission (FCC) has released the first report and order regarding the application of ultra-wideband (UWB) communication devices [1]. The antennas are an essential part of such systems as of any wireless system. All antenna’s properties depend strongly on the frequency. Therefore, the transmitted waveform is filtered by the antenna structure. The ultra-wide bandwidth allows for resolving the fine structure of the transient transmitting and receiving performance of the antenna. For the free-space propagation channel, the channel impulse response depends only on the antennas’ filtering characteristic. In the case of a line-of-sight (LOS) channel, the energy content of the channel impulse response is dominated by the direct path, which again is filtered by the transient responses of the employed antennas. For the analysis of environments with the condition of rich multipath like non-lineof-sight (NLOS), one has to take into account that the filtering characteristic of the antenna has not only an impact on This is an open-access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
the frequency domain and the time domain but has also a spatial component. This results in different filtering characteristics for different directions and leads to a weighted excitation of the different paths. Therefo
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