The expansion of sources of renewable energy requires e.g. the designation of suitable areas for wind turbines (WT) and photovoltaics installations. Tall WT may interfere with terrestrial navigation and radar installations due to reflections of the electromagnetic waves. They may also emit infrasound noise. These issues may pose restrictions on building permits of WT.To be able to evaluate and score the profitability of onshore WT locations, the prevailing wind direction and speed need to be assessed up to 250 m height. As the nacelle of WT are installed at 150 m up to 250 m offshore, maintenance and repair of shafts and gearboxes are difficult to implement and costly. The quality and mechanical precision of manufacturing of WT parts are therefore essential for a long lifetime and a good return-on-invest.PTB as the National Metrology Institute of Germany has successfully completed research projects that address these issues. This paper describes each topic and gives an overview about the infrastructure such as the Wind Competence Centre (CCW) at PTB, the results of the projects, and their contributions to the expansion of renewable energy.

The aim of this publication is to provide an overview of the recent advances of the XML schema for digital calibration certificates.The motivation and benefits of digital calibration certificates is explained and the basic requirements to which the DCC complies are stated in Section 1.A representative selection of changes is presented and explained in Section 2; and finally, conclusions are drawn, and an outlook on further work is given in Section 3.

One of the benefits of the Digital Calibration Certificate (DCC, [1] and [2]) as shown by PTB is to have flexible ways to transform the resulting DCC document since it is a digital document.In order to better visualise the content for human beings, or for a transitional period to print an analogue copy of the DCC XML [3] document with sign and seal, a feature for transforming the DCC to a human readable form is needed.We will call this form human readable (HR) (see Fig. 1), and it is an optional part of the DCC.This paper will show how to generate the human readable form of the DCC by using the eXtensible Stylesheet Language (XSLT [4]).In section 1 we will give a short review of the DCC schema (XSD) and describe the structure of an exemplary DCC (XML).In section 2 we will suggest how to generate the human readable of a DCC document.First, we will discuss for which purpose the human readable can be used.Then, we show how the human readable can be generated by using XSLT.Finally, we will give an outlook on future steps and topics to be solved.

With contributions from Jochen Bredemeyer, Thomas Kleine-Ostmann, Jens Werner, Jens Wellhausen, and Heyno Garbe

The aim of this publication is to provide an overview of the prototype digital calibration certificate. The role of calibration certificates is explained and the differences between paper-based and digital calibration certificates are described in Section 1. All specifications of the digital calibration certificate are given in Section 2; security aspects are discussed in Section 3; and finally, conclusions are drawn in Section 4.The prototype of the digital calibration certificate (DCC) was first described in the PTB-Mitteilungen [1] in 2017.

We introduce a new tunable reflectarray element for an operation frequency of 26 GHz in the k-band. It is shown that a 340∘ continuous tunning range of the reflected wave can be accomplished by using an aperture-coupled patch antenna with only one single varactor diode. The simplified design and the small needed space make it usable for k-band reflectarrays with many elements. The functionality of the reflectarray element is explained and the crucial parts are analyzed. The approach to get a full phase shift is discussed in detail. A bias-T is developed to provide the control voltage to the varactor diode without interfering with the high frequency path. The high frequency path and the DC-path are decoupled by 39 dB using a bias-T. A commercial off-the-shelf varactor diode is selected and its functionality at 26 GHz is verified. Therefore, a test printed circuit board with through, reflect, line standards is developed to de-embed the varactor diode and to evaluate it with a vector network analyzer. The reflectarray is simulated in a unit cell with plane wave excitation and periodic boundary condition using the simulation software package CST Microwave Studio™.

The radar echo of a large wind turbine (WT) is investigated in the C band: An unmanned aerial system (UAS) is used to perform a reflectivity measurement across the flight altitude using a passive bistatic radar (PBR) constellation of a non-cooperative precipitation radar transmitter in horizontal polarization. This is done at various distances to check if far field conditions apply to derive a radar cross section (RCS). As a fully independent method, a monostatic FMCW radar is installed on ground at certain distances to the WT. The results of both methods are compared against each other regarding the applicability of the RCS.

The impact of scattering objects such as wind turbines (WTs) and other buildings on the VOR has been addressed in various publications. Nevertheless, a practically feasible possibility to predict especially the Doppler VOR bearing error during the building’s planning phase is challenging, since a electromagnetic model of that facility must replicate its radiation with both CSB and SBO antennas in a complex scenario that is large w.r.t. the wavelength. A new time domain method will be introduced to address this topic for dynamically disturbed environments. Separating its frequency modulated (FM) and amplitude modulated (AM) content, the indicated bearing is calculated subsequently by determining the corresponding phase difference. Within the research project WERAN, an UAS-based (here: octocopter) platform with dedicated antennas, receivers and adapted signal processing was developed. Using this device, it is now possible to measure separately small phase errors on the 30Hz FM and AM signal components. According to the prediction, bearing errors due to existing wind farms are now traceable at specific positions in the airspace. Hence, the numerical results can be validated by in situ measurements of real DVOR signals-in-space in the environment of real WTs. The presentation will give an overview on the numerical method and the validation cases.

The impact of scattering objects such as wind turbines (WTs) and other buildings on the VOR has been addressed in various publications. Nevertheless, a practically feasible possibility to predict especially the Doppler VOR bearing error during the building’s planning phase is challenging, since a electromagnetic model of that facility must replicate its radiation with both CSB and SBO antennas in a complex scenario that is large w.r.t. the wavelength. A new time domain method will be introduced to address this topic for dynamically disturbed environments. Separating its frequency modulated (FM) and amplitude modulated (AM) content, the indicated bearing is calculated subsequently by determining the corresponding phase difference. Within the research project WERAN, an UAS-based (here: octocopter) platform with dedicated antennas, receivers and adapted signal processing was developed. Using this device, it is now possible to measure separately small phase errors on the 30Hz FM and AM signal components. According to the prediction, bearing errors due to existing wind farms are now traceable at specific positions in the airspace. Hence, the numerical results can be validated by in situ measurements of real DVOR signals-in-space in the environment of real WTs. The presentation will introduce the numerical method and the measurement platform and give an overview on the validation cases.

In an intercomparison organized within the framework of the German Calibration Service (Deutscher Kalibrierdienst – DKD), seven different calibration laboratories participated in the measurement of the antenna factor for three different antennas according to different standards. Between August 2017 and April 2018, measurements have been performed on a hybrid antenna, a logarithmic-periodic antenna and on an Open Ended Waveguide.

In this paper, we describe measurement results of the signal-in-space of very high frequency (VHF) omnidirectional range (VOR) facilities. In aviation VOR are used to display the current course of the aircraft in the cockpit. To understand the influence of wind turbines (WT) on the signal integrity of terrestrial navigation and radar signals, the signal content and its changes, respectively, must be investigated. So far, only numerical simulations have been carried out on the frequency-modulation (FM) part of the Doppler-VOR (DVOR) signal to estimate the influence of WT on DVOR. Up to now, the amplitude-modulated (AM) part of the DVOR was not assessed at all. In 2016, we presented an unmanned aerial system (UAS) as a carrier for state-ofthe-art radio-frequency (RF) measurement instrumentation (Schrader et al., 2016a, c; Bredemeyer et al., 2016), to measure and to record the true signal-in-space (both FM and AM signal) during the flight. The signal-in-space (which refers to time-resolved signal content and field strength, respectively) is measured and sampled without loss of information and, furthermore, synchronously stored with time stamp and with precise position in space, where the measurements were taken.

The disturbing effects of scattering objects such as wind turbines (WTs) and other buildings on the flight navigation aid Doppler very high frequency omnidirectional radio range (DVOR) have been addressed in previous publications. Nevertheless, a practically feasible possibility to precisely and consistently predict the DVOR bearing deviation before the buildings’ construction is still missing. In this contribution, a method based on numerical simulations is presented which allows calculating the DVOR receiver's antenna voltage in the time domain for dynamically disturbed environments. Separating its frequency modulated and amplitude modulated content, the indicated DVOR bearing is calculated subsequently by determining the corresponding phase difference. Finally, the calculation results are validated by in situ measurements of DVOR signal disturbances in the environment of eight WTs.

Antenna calibration is classically performed assuming far-field conditions. With increasing computational power available, numerically demanding near-field to far-field transformation algorithms are becoming more important. This paper shows how modern near-field to far-field transformation algorithms can be used to precisely calibrate antennas. In addition to the actual algorithm, this paper also demonstrates how the calculated far-field data can be used to calculate the electric field strength in front of arbitrary antennas. This post processing step is of special importance for the traceable calibration of electric field strength meters.

An intercomparison in the framework of the German Calibration Service (Deutscher Kalibrierdienst – DKD) was carried out. Two different travelling standards were used to measure the 10 % to 90 % rise time of a pulse generator and the 10 % to 90 % rise time, −3 dB bandwidth and attenuation at 500 MHz of an oscilloscope. Fourteen participants performed the measurements from September 2015 until May 2016.

The Netherlands Organisation for Applied Scientific Research TNO is regularly tasked to perform windfarm-radar impact studies. The requests most often come from windfarm operators in Europe, but studies for an operator based in Australia have also been performed. Referring to terminology introduced by Eurocontrol’s wind-turbine task force (WTTF), both simple engineering assessments (SEAs) and detailed engineering assessments (DEAs) are conducted. Certain civilian or military ANSPs (air navigation service providers) do, however, not follow Eurocontrol’s guideline, in which case a DEA is conducted, regardless of the distance between the radar system and the windfarm. The analyses may involve both primary and secondary radar systems. The main ingredients of TNO assessments are briefly sketched. Subsequently, the judgement process, i.e., the criterion upon which the verdict on windfarm construction is based, is discussed. It is observed that ANSP’s do not always utilize a well-defined criterion, which gives rise to subjectivity.

A passive bistatic radar (PBR) constellation of a radar transmitter, wind turbines as targets and an unmanned aerial system (UAS) carrying the receiver is used for scattering measurements and discrimination between single wind turbine (WT) echoes. Since the geometry is fully known, the radar echo gained from the WT is related to its reflectivity across the flight altitude of the UAS. These results are compared against computer simulations of the same scenario.

In the project WERAN it is also aimed to determine the interaction of wind turbines (WT) with radar signals. The evaluate the strength of single a single WT reflecting radar transmissions, measurement campaigns with multicopters (UAS) have been carried out at various radar sites in the L (Air Defense), S (AD and ATC) and C band (Precipitation radar). The presentation focusses on radar echoes received at different UAS flight altitudes and distances to the scatterers. It is useful to analyse the radar return both in the time and frequency domain to detect static and time variant signal components. Some results will be shown and discussed. In the follow-up project WERAN plus there are some additional airborne vehicles in use to carry the measurement equipment. Some ideas of what can be expected from measurements at higher altitudes and moving at horizontal speed will be shared.

The project WERAN aimed to determine the interaction of wind turbines (WT) with signals of terrestrial navigation systems such as VHF omnidirectional radio ranges (VOR) and RADAR. One of the main goals of the project was to quantify the additional VOR bearing error caused by wind turbines by means of measurement and numerical simulations. In this presentation we will discuss the results of on-site measurements and compare those with numerical simulations. A remote- controlled multicopter with precision localization has been used as measurement platform. It carries a compact but capable high frequency instrumentation and integrated antennas to measure simultaneously both the AM reference signal and the FM signal of a Doppler VOR as true signal-in- space. Actual position, time stamp and measurement data are simultaneously stored at the platform. These measurements give insight into the signal content and signal integrity of VOR with and without WT. Furthermore, varying operational conditions of WT such as rotation vs idle state or angular movement of the nacelle may have different influence on the additional bearing error. During the follow-up project WERAN plus we will use the measurement data and simulation results to derive a model-based assessment tool. This will allow for prediction of the degree of interference (additional bearing error) of additional WT in the area around VOR with given topology.

We describe the development of a system for measurements of electromagnetic field strength distributions and on-site antenna calibrations based on an unmanned aerial system (UAS). The commercially available octocopter was improved by a state-of-the-art GNSS navigation system and a shielding against electromagnetic harsh environments. We have designed, built and tested the FPGA-based data logging hardware as well as several RF frontends and antennas to be mounted on the UAS. We show first applications of our UAS measuring the interaction of wind turbines and terrestrial navigation systems such as DVOR and radar systems used for air traffic surveillance.

The paper presents the characterization of a 300-GHz transmission system for modern digital communications. The quality of the modulated signal at the output of the system (error vector magnitude, EVM) is measured using a vector signal analyzer. A method using a digital real-time oscilloscope and consecutive mathematical processing in a computer is shown for analysis of signals with bandwidths exceeding that of state-of-the-art vector signal analyzers. The uncertainty of EVM measured using the real-time oscilloscope is open to analysis. Behaviour of the 300-GHz transmission system is studied with respect to various modulation schemes and different signal symbol rates.