Prof. Dr.-Ing. Ingo Gaspard

Next decade will encounter a 1000-fold increase in capacity demand for wireless communications systems which will not be supported by microwave band below 6 GHz where most wireless technologies operate today. Besides reducing cell size and applying enhanced signal processing the use of new frequency spectrum above 30 GHz i.e. at mm wavelengths especially for indoor scenarios is suggested. In order to design communication systems at these frequencies in an optimal way a sound knowledge of the radio channelproperties is mandatory.When increasing frequency, building material surfaces, like walls, which interact with the wave travelling from transmitter to receiver start to be rough with respect to the wavelength and propagation mechanisms like reflection becomes more complicated because besides scattering into diffuse directions depolarization of the impinging wave takes place. Starting with measurement results from an extensive measurement campaign at868MHz ISM band taking into account polarization effects this talk will present results on different combinations of antenna polarization at TX and RX end in order to mitigate fading effects in smart home applications. In order to further validateand investigate thisconcept the implementation and parameterization of a ray tracing system level simulation tool is described and simulation results show clearly average advantages over a number of different links in a given scenario by using the combination of a linearly and a circularly polarized antennasat the two ends of each communication link in the envisaged smart home indoor application.As the next topic of this talk a vector network analyser based measurement system including the design, implementation and measurement based characterization of two different conical horn antennas for the 38 GHz band is described. Based on this system the realization and evaluation of an indoor measurement campaign where scattering experiments at a typical slightly rough indoor wall are carried out is reported. Further a simulation approach parameterized by these measurement results for investigation of depolarization caused by single scattering at slightly rough surfaces at 38 GHz based on the geometric optics (GO) approach to solve Kirchhoff’s approximation is presented. Scattering surfaces are modeled by two-dimensional random Gaussian height distributions characterized by correlation length and standard deviation. At each surface element of the rough surface the impinging wave is decomposed into one component parallel to the plane of incidence and one perpendicular to the plane of incidence. For each of the two components Fresnel reflection coefficient –which is in general different for the horizontal and vertical polarized part of the wave with respect to the local coordinate system of the surface element -is applied and the resulting wave into the direction of receiver is calculated in global coordinate system. At an arbitrary receiver position the partial waves of all surface elements forming the rough surface are coherently addedaccording to polarization. Weighting of the transmitted wave field as well as of the received wave field according to realistic, measured antenna pattern is also applied. The described simulation approach allows for a complete description of the polarization properties of the received signal according to Mueller matrix. Simulation results for different parameter sets like incident/scattering angle, frequency, roughness, polarization of field incident at rough surface etc. will be given and show that there is a significant depolarization –seen by an increased cross-polar ratio after reflection –even for surfaces with rms height variation as low as 0.1 mm.

Biography:

Since 2009 Ingo Gaspard is professor at Darmstadt University of Applied Sciences and is teaching courses in RF/microwaves, antennas, radar, EMC, fields & waves and measurement technology. Prior to this position he was working with Deutsche Telekom and subsidiaries for more than 15 years in the areas of planning, operation and validation of mobile radio systems, international standardization bodies and corporate research in mobile radio and broadcast systems. Ingo was working as expert and project manager in many national and international/EU funded research projects during that time. Educated at the Technical University of Kaiserslautern he holds a Dipl.-Ing. degree from there and a Ph.D. degree from Technical University of Darmstadt. He is regularly active as a reviewer for IEEE Antennas & Propagation society, member of URSI, commission C, member of the editorial board of journal “FREQUENZ” and holds more than 10 patents.

Address:Darmstadt University of Applied Sciences, , Darmstadt, Germany