Georg Zimmer

Navigation Signal Disturbances by Multipath Propagation – Scaled Measurements with a Universal Channel Sounder Architecture

Abstract The performance of navigation systems is always reduced by unwanted multipath propagation. This is especially of practical importance for airborne navigation systems like the instrument landing system (ILS) or the VHF omni directional radio range (VOR). Nevertheless, the quantitative analysis of corresponding, potentially harmful multipath propagation disturbances is very difficult due to the large parameter space. Experimentally difficulties arise due to very expensive, real scale measurement campaigns and numerical simulation techniques still have shortcomings which are briefly discussed. In this contribution a new universal approach is introduced on how to measure very flexibly multipath propagation effects for arbitrary navigation systems using a channel sounder architecture in a scaled measurement environment. Two relevant scenarios of multipath propagation and the impact on navigation signals are presented. The first describes disturbances of the ILS due to large taxiing aircraft. The other example shows the influence of rotating wind turbines on the VOR.

EMC analysis including receiver characteristics - pantograph arcing and the instrument landing system

This contribution presents a sophisticated compliance study, whether emissions of transient sparks occurring between pantographs of rails and overhead lines can interfere with receivers of the instrument-landing-systems (ILS) onboard aircraft. Though the investigated interference scenario actually is quite specific and arose in the context of the enhancement of the airport Frankfurt in Germany it comprises several fields of electromagnetic compatibility where yet insufficient approaches exist. In particular, absolute field strength measurements of transient signals in a non-ideal measurement railway environment are conducted. Another new aspect in this study is, that the individual receiver characteristics are taken into account, e.g. non-linearity and band pass behavior, where usually only simple continuous wave signals in an interference path loss model are considered. Consequently, a setup is presented, where an individual measured interference signal from a real environment is synthesized and fed into a real EMC sink. This procedure however, could be generalized to any other receiver or interference source.

Vectorial channel sounding in a reverberation chamber - measuring dynamic behaviour

The key aspect of reverberation chambers (RC) is the statistic behavior of the field inside including the influence of the moving, respectively rotating mode stirrer. By means of a vectorial channel sounder presented in this contribution the dynamic influences of the stirrer are investigated with respect to its mechanical relaxation time and its efficiency. Additionally, the ability of vectorial channel sounding allows to simultaneously measure the influence of different antenna orientations and polarizations on time-variant propagation channels investigating spatial-dependent effects in the RC. Measurements are done on a small time scale that is not accessible by standard field probe sampling times. Results also indicate dynamic effects of the RC even for a static case, where the RC may be mechanically excited by external sources, respectively vibrations.

Electromagnetic scattering problems -Numerical issues and new experimental approaches of validation

Electromagnetic scattering problems, thus the question how radiated energy spreads when impinging on an object, are an essential part of wave propagation. Though the Maxwell’s differential equations as starting point, are actually quite simple,the integral formulation of an object’s boundary conditions, respectively the solution for unknown induced currents can only be solved numerically in most cases.As a timely topic of practical importance the scattering of rotating wind turbines is discussed, the numerical description of which is still based on rigorous approximations with yet unspecified accuracy. In this context the issue of validating numerical solutions is addressed, both with reference simulations but in particular with the experimental approach of scaled measurements. For the latter the idea of an incremental validation is proposed allowing a step by step validation of required new mathematical models in scattering theory.