Werner Sorgel

Influence of the antennas on the ultra-wideband transmission

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 to , that is, a bandwidth of , for unlicensed use with up to 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 antennas 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.

Transient responses of a Vivaldi antenna and a logarithmic periodic dipole array for ultra wideband communication

Antennas are mandatory system components for UWB communication systems. The paper presents a comprehensive approach for the characterization of UWB antenna concepts. Measurements of the transient responses of a LPDA and a Vivaldi antenna prove the effectivity of the presented model.

Deterministic UWB Wave Propagation Modeling for Localization Applications based on 3D Ray Tracing

For the assessment of radio based localization applications deterministic channel models are required that allow for the simulation of wave propagation in realistic environments. This paper describes the extension of the deterministic narrow-band wave propagation modeling approach of ray tracing to ultra wideband (UWB) channels. A channel model is presented that permits the simulation of wave propagation in realistic three-dimensional environments over the entire frequency range of UWB applications from 3.1 to 10.6 GHz. Simulation results for the impulse response and the power delay profile in a typical indoor scenario are shown. From a set of simulation results statistics are extracted and compared to already standardized statistical UWB channel models

Impulse responses of linear UWB antenna arrays and the application to beam steering

Ultra wideband (UWB) systems enable the transmission of short pulses with a very high time resolution. The application of UWB arrays leads to small beam widths without sidelobes even for sparse arrays with large element spacing. However the transmitted and received signals are subject to distortions due to the dispersive properties like ringing and filtering of the antennas. These effects are analyzed for true time delay beam steering in the paper by the means of the antenna array impulse response. This is derived for the example of a linear array for the frequency range of 3.1-10.6 GHz. The theoretical results are verified by measurements.

A small planar inverted F antenna with capacitive and inductive loading

The development of very small antennas significantly influences the miniaturization of handheld devices. A planar and symmetric antenna is built up. A capacitive loading for this planar inverted F antenna (IFA) is presented. For a further size reduction, an inductive loading is investigated. The method of moments (MoM) is used to model the antenna and measurements are carried out for verification.

Characterization of multipath clusters with ray-tracing in urban MIMO propagation environments at 2 GHz

For the design of MIMO (multiple input multiple output) systems, channel models are required that properly describe the behavior of the physical channel. The propagation environment around a mobile station (MS) and a base station (BS) is a multipath environment. Multipath components can be grouped together into so called clusters. We define a cluster as a group of paths with similar directions of departure or arrival in azimuth and elevation and similar time delay of arrival. A 3D deterministic ray-tracing tool is used to calculate the double-directional MIMO channel. The advantage of deterministic ray-tracing in contrast to measurements is that ray-tracing offers the possibility of detailed characterization of all multipaths and investigation of the propagation effects without any constraint concerning the antenna or the measurement equipment. A new automatic procedure to identify clusters in azimuth, elevation and delay at the transmitter and the receiver from ray-tracing data is presented. Based on the ray-tracing simulations, we propose a new iterative procedure to extract multipath clusters. The extracted parameters show clearly that, in macrocellular environments, the number of MS-clusters is much greater than the number of BS-clusters. The presented cluster characteristics help to parameterize MIMO channel models and to make simulation results more realistic.

An adequate channel model for ultra wideband localization applications

In this paper a suitable approach to the deterministic modeling of ultra wideband channels has been presented. The developed channel model allows for wave propagation modeling within realistic three-dimensional environments and thus builds an ideal basis for the assessment of localization applications. The presented simulation results and the comparison with the IEEE 802.15.3a model show that this model delivers accurate and realistic channel impulse responses

Frequency dependence of correlation coefficients in ultra wideband antenna arrays

In order to optimize the performance of multi-antenna systems for communications applications it is desirable to have little correlation between the signals at the different receiving antennas. This can be achieved by choosing appropriate antenna characteristics and positions. For ultra wideband (UWB) applications this task is even more challenging, since correlation coefficients are dependent on frequency. This paper presents an investigation of the frequency dependence of the correlation coefficients of a linear antenna array in an UWB indoor propagation scenario. The investigated array itself consists of omni-directional elements. Thus only the correlation behaviour that is introduced by the propagation channel is regarded. It turns out from the conducted simulations that the correlation coefficients are highly altering with frequency and distance of the antennas. Furthermore, they severely depend on the position of the array inside the room. The simulation results show that, even if omni-directional antenna elements are used, with a dedicated placement of the antenna array pretty low correlation coefficients can be obtained over the entire frequency range regulated by the FCC for UWB applications.

Electromagnetic Characterization of Ultra Wideband Antennas

Ultra Wideband applications in communication and Radar have stimulated research for several 10 years. The possibilities for high resolution and high data rates have been the driving visions. Especially the military research added the feature of low probability of detection. Since the United States Federal Communication Commission (FCC) has opened the spectrum from 3.1 to 10.6 GHz for unlicensed, low power applications a new dimension is added to ultra wideband research. This papers focuses on state of the art research in ultra wideband antennas. Especially the Vivaldi antenna and the logarithmic periodic dipole array (LPDA) of small size for applications in communications are treated. It is shown that both can handle very well the more than 100 % relative bandwidth. While the Vivaldi antenna shows low distortion and only small ringing, the logarithmic periodic dipole array exhibits high distortion, ringing and higher order modes of radiation. This behavior has to be optimized together with the modulation schemes for ultra wideband communications.

Broadband multimode antennas for MIMO applications

This paper presents compact broadband multimode antennas for MIMO and diversity applications. The antenna system is riot based on spatial diversity. as usual MIMO system, but on a combination of pattern and polarisation diversity. Different modes of self-complementary spiral antennas we used to decorrelate the signals. It is shown that only one antenna is necessary to receive three uncorrelated signals, thus the space required to place the MIMO antenna is very small.