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Impact of Dynamic Scatterers upon Frequency- and Amplitude-Modulation

Hard Copy
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Impact of Dynamic Scatterers upon Frequency- and Amplitude-Modulation (English shop)

A Theoretical and Practical Treatise in the Context of the Doppler-VOR and Wind Turbines

Björn Neubauer (Author)


Table of Contents, PDF (160 KB)
Extract, PDF (630 KB)

ISBN-13 (Hard Copy) 9783736975064
ISBN-13 (eBook) 9783736965065
Language English
Page Number 348
Lamination of Cover matt
Edition 1.
Publication Place Göttingen
Place of Dissertation Braunschweig
Publication Date 2021-10-20
General Categorization Dissertation
Departments Physics
Theoretical physics (including physics of oscillation and waves)
Measurement and controlling engineering
Aerospace engineering
Electrical engineering
Common electrical engineering
Telecommunications and communications engineering
Keywords amplitude modulation, Amplitudenmodulation, analytical expression, analytische Ausdrücke, bearing intelligence Position, building restricted area, Anlagenschutzbereich, Doppler shift, Dopplerverschiebung, Doppler VOR, Drehfunkfeuer, DVOR, dynamic scatterer, dynamisches Streuobjekt, energy transition, Energiewende, frequency modulation, Frequenzmodulation, modulation, Modulation, multipath propagation, Mehrwegeausbreitung, navigation, system Navigationssystem, phase shift, Phasenverschiebung, probability distribution, Wahrscheinlichkeitsverteilung, probability distribution, Wahrscheinlichkeitsverteilung, renewable energy, erneuerbare Energien, scaled measurement environment, skalierte Messumgebung, scaled terrain topology, skalierte Geländetopologie. scatterer Streuer bzw. Streuobjekt, signal integrity, Signalintegrität, superposition of oscillations, Superposition von Oscillationen bzw. Wellen, terrain topology, Geländetopologie, time varying signal strength, zeitveränderliche Signalstärke, wind energy, Windenergie, wind farm, Windfarm, wind turbine, Windenergieanlage (WEA), Rundstrahler, Navigationsempfänger, navigation receiver, bearing error, konventioneller Drehfunkfeuer, conventional rotating beacon, requenzmodulierte Signalkomponente, requency-modulated signal component, Simulationswerkzeug, simulation tool, Winkelgeschwindigkeit, angular velocity, Anderson'scher Peilungsfehler, Anderson’s Bearing Error, Signalverschlechterung, signal deterioration, Dreiecksausrichtung, triangular alignment, Rotationsebene, Plane of Rotation, Senderhöhe, Emitter Height, Eulersche Gleichung, Euler Equation, Kettenregel, Bessel-Funktion, chain rule

In 1959 Anderson et. al publish their paper „The CAA Doppler Omnirange”. In that contribution they present their analytically derived receiver‑model for quantifying the bearing error of the Doppler VOR (DVOR) due to multipath propagation. At that time this model exclusively serves for comparing the susceptibility of the DVOR with the one of its precursor which is the conventional VOR. For this purpose, they take the impact of a static omnidirectional scatterer solely upon one signal component into account, which is the frequency modulated one.

Due to the number of already installed wind turbines and especially due to the desire to install way more turbines, the signal integrity of the DVOR has become a very timely topic in Germany in the context of renewables energies.

In this dissertation Anderson’s basic generic model is both improved and substantially extended with respect to the impact of wind turbines upon the multipath signal.
In the first part of this work Anderson’s error model is quantitively expended with respect to the relative amplitude of the scattering path. Furthermore, the analytical model is fundamentally improved with respect to quality: For the first time the analytical model allows to take the dynamic effects of wind turbines into account, i.e. both Doppler shifts as well as an additional amplitude modulation due to the scattering object — namely the wind turbine. Additionally, this analysis is carried out for the DVOR’s reference provided by an amplitude modulated signal component, which has been completely neglected so far by the current state of the art.

These analytical models allow for extensive parameter studies, which are applicable e.g. for the validation of both numerical simulation tools as well as approaches by measurements.
In the second part of this work the dynamic impact of wind turbines upon the DVOR’s bearing intelligence is investigated by measurements. This is carried out in an environment scaled with a ratio of 1:144. It utilizes the equipment realized within the projects “Sk-ILS” and “min-Vor-Win” and expands it by inventing a procedure for crafting and electromagnetically characterizing voluminous scattering bodies. These allow for a systematic analysis of the impact of terrain topologies.

A variety of measurements and the corresponding fundamental analysis address: Doppler shifts and Doppler spectra depending on the orientation of the plane of rotation, the blades’ shape, revolutions per minute, and the position of the turbines as well as the amplitude and width of Doppler spectra.

Fundamental results of this work are e.g.: A 10 km safety‑radius of the DVOR’s protective area, up to now applied in Germany and as well recommended by the ICAO, can be considered way to restrictive. Furthermore, the receiver settings play a crucial role, when determining the bearing error. Thus, stating the latter makes it mandatory to state the receiver settings as well.


To produce green energy efficiently, signal interferences by wind-turbines is a significant problem for aeronautical radio navigation systems. From the view point of safety in aircraft operations, interferences of electromagnetic waves should be paid attention to not only VOR but also other systems such as DME, radar, and communication systems. Therefore, this fundamental research has the potential to contribute to the entirety of the aeronautical industry – in terms of methods of operation, safety management, and radio systems deployment. The followings are my review comments.
In Chapter 1, background is described. The basic theory is indicated, and then the issues of wind-turbines are noted. VOR as well as Doppler VOR are the main focuses in this thesis. The author’s mention of the importance and strategy of today’s green energy produced using wind-turbines and the problems of electromagnetic waves caused by the blades is a nice point. Given that the safety of aircraft operation and the huge costs for wind-turbine deployment are strongly related with each other, the influences of signal interference on with (D)VOR should be investigated. This chapter notes the technical provisions, the present assessment for (D)VOR, and the environment in Germany, where the wind turbine and (D)VOR systems are located. The main point of the thesis is easily understood by the reader.
In Chapter 2, the principle of DVOR is explained. In Chapter 3, signal deterioration of FM-components by static scatterer is described. The formulation is well-known, but the way it is constructed helps readers to understand the principles, including scatter waves. The relationship between the receiver antenna (location and azimuth angles) and errors is shown. There is one mistake on line 7 of page 20 where Figure 10.2 is referred to as Figure 3.2. Considering the dynamic scatter, this chapter is fundamental and quite important for analyzing signal interference from wind-turbines.
Next, the author expands on the formulation for the static case to cover non-static situations in Chapter 4. A receiving antenna loaded on an aircraft obtains three main types of data: static scattered fields, doppler shifted scattered fields, and amplitude modulation from wind-turbines with moving blades. This expansion of the formulation is explained in detail through the procedures. The effects of doppler shift can be easily understood. In contrast to the FM-components discussed in Chapters 3 and 4, signal deterioration of AM-components caused by non-static scatterers is discussed in Chapter 5. Some relation can be confirmed from the results, which include receiver allocation (distance and angle), phase shift, and errors as parameters.
In Chapter 6 is an interesting element of the thesis. The method of assessment is an important factor for operators and developers. Assessment should be classified corresponding to the positional relation between the source(emitter), the receiver, and the scatterer. This means the areas are evaluated in precise, approximate and simple assessments. This thesis covers the approximation, but this case would be often used in real situations.
In Chapter 7, the measurement setup is described. A scaled model is employed. This measurement is conducted for the frequency of the ILS (Instrument Landing System). The operating frequency is 16 GHz, and a metallic sphere is selected as the scatterer. The results show that the analytical values and actual measurement values coincide well. The value of RCS (radar cross section) for the sphere is confirmed.
In chapter 8, the main measurement concept for (D)VOR is described. The schematic hardware setup used for the channel sounding is shown. The frequency of 15.9 GHz is selected – the actual (D)VOR frequency is approximately at 110 MHz. Other devises and apparatus are introduced here. The antennas used and their specifications are described in Chapter 9. A patch antenna and horn antennas are chosen in this thesis. In Chapter 10, the influences of terrain topology are evaluated. Scattering from terrain profiles is also an important factor to the total received fields. Therefore, the behavior of electromagnetic fields
affected terrain-roughness should be investigated for radio propagation. The author presents the differences from materials and the effects of scaled generic hillsides. I think the latter case especially is very interesting, and the thesis demonstrates diffracted fields from the hill. In some cases, wind-turbines are deployed on mountains to generate more electric power. Considering real signal environments, receivers on aircraft catch the direct path from the emitter including scattered waves from terrain and obstacles like wind-turbines. Consequently, the values shown in this chapter are a performance index of (D)VOR.
In Chapter 11, fabricated scale-model wind turbines are introduced referred to as K1 and K2. The scale is 1:144. The length of the blades is approximately 40 cm. In Chapter 12, the author discusses the effects of these scale-model wind-turbines. The main results are shown here. Based on these results, the author indicates the impact of wind-turbines on propagation channels. Measurements were performed at an open area test site. The angle between the emitter and the receiver was 45 degrees. The distance from the emitter to the scatterer was 21 m, which corresponds to 3 km in actual scale. The doppler spectrum could be detected in the experiment. In addition, the results is confirmed that the shape of blades (4 shapes were tested) affects the characteristics of the doppler spectrum. The different rotating angle of wind-turbines was also demonstrated. The effect of wind-turbines was shown to be maximized at half of the angle between the emitter and the receiver. The measurement scenario with three wind turbines located on the top of a hill model is interesting. In this scenario, the impact of the wind-turbines is relatively small in comparison to measurement without a hill model. Of course, the relationship between the height of the emitter and the scatterer affects the impact of wind-turbine. Finally, in Chapter 13, the measurement results for line of sight are shown. This is the case of wind-turbines located at the midpoint between the emitter and the receiver. It seems the shadow case of the wind-turbine or the transmitted case for the receiver. Through this measurement, we can understand the characteristics of radio waves at the back of blades. As we can imagine, the impact of the wind-turbine is maximum when the scatterer is at an angle of 0 or 180 degrees to the emitter. This measurement result is useful for the developers considering the wind-turbine placement.
In Chapter 14, the thesis is concluded. This research was carried out from both measurement and theoretical viewpoints. Topics ranging from basic mathematics to extended forms for the author’s purpose were addressed, and the measurement scenarios were well-considered to fit the real signal environments. Through the thesis, readers can clearly understand the social issues related to green energy for the aeronautical industry and the importance of assessment. The thesis is organized into sections such as introduction, AM-and FM- components in (D)VOR, general concept of the purpose, used components, results of doppler shift, and so on. I think that this result will help assist the ongoing introduction of green energy,

Junichi Honda, Tokyo (Japan)
Electric Navigation Research Institute (ENRI)
25th May 2022