A technique is proposed that improves wireless communication channels in fading environments. The device creates a map of channel measurements. The device then moves its antenna to positions of the previously measured maximum within its reach. Proof-of-concept measurements were performed for smartphone-sized devices in an office environment. A quarter-wavelength monopole antenna for the 2.4 GHz frequency band successfully kept the channel at local maxima. The results show that small antenna movements over half of a wavelength are sufficient to keep the channel in local maxima, to avoid deep fading notches, and to improve channels over state-of-the-art antennas that move with their devices. A channel model for the wireless communication channel of mobile devices with channel maximum antennas is proposed based on the measurement results.

This work investigates how well mobile wireless communication channels can be kept static during device movements when the antenna performs appropriate counter-movements. A prototype is built and proof-of-concept experiments are performed for linear movement in the 2.45 GHz ISM frequency band in an anechoic chamber and in a static office environment. The technique is assessed quantitatively. The measured data show that fluctuations of receive power can be decreased by a factor of thousand as the antenna no longer experiences small scale fading. Changes in the phase are brought down to values smaller than 10° and no longer scale with the traveled distance. Mathematical channel models are derived from the measurements.

A pattern reconfigurable antenna for 2.6 GHz LTE is flush-mounted in a chassis antenna cavity. The driven element is a top-loaded monopole, that is steered based on the electronically steerable parasitic array radiator (ESPAR) principle. The radiation pattern can be configured in 45 degree steps, e.g. front, diagonal front-right, right, etc. The cavity prototype is made from carbon fiber reinforced polymer and includes a chassis mockup. Antenna performance is evaluated based on measured gain patterns, which show that the antenna retains its reconfiguration capabilities when it is flush-mounted. Further, a parametric measurement study with regards to antenna height inside the cavity is performed to investigate the option of mounting an electronics module underneath the antenna.

An automotive concept for vehicular communications is proposed that utilizes the potential of the roof area for antennas. Antennas are distributed in cavities and on shelves in the center and on the front and rear roof ends. The arrangement of antennas on the roof allows better radiation to the front and back of automobiles than shark-fins and single cavities. Combining several modules provides space for further antennas, sensors and integrated front-ends, as well as better spatial separation for multiple-input multiple-output (MIMO) arrays beyond 5G, and cooperative connected and automated driving. A prototype was developed and built into a car chassis. Measured data were analyzed and evaluated in the view of coverage for vulnerable road users and on correlation for MIMO.

Cooperatively driving cars benefit from increased coverage towards driving direction for communication with vulnerable road users. Antenna cavities were designed, prototyped and measured for integration into car roofs above the windshield. Two different antenna cavities were investigated. First, an antenna cavity made from carbon fiber reinforced polymer was measured without a vehicle, to obtain general results without model specific influence. Second, a metal cavity was built into the roof of a sedan type passenger car to include the marked effects of the car body and provide a proof of performance. Gain patterns were measured in anechoic chambers. Results show that the antenna structure and mounting position are suitable for omnidirectional radiation with increased radiation towards low elevation angles in driving direction.

A conformal antenna cavity for the mononoque of racing cars is proposed and prototyped from carbon-fiber reinforced polymer. Performance is evaluated with measured S-parameters and measured radiation patterns.

Cavities built into the vehicle chassis have recently emerged as receptacle for hidden antennas. In the automotive sector they potentially replace the roof mounted shark-fin antenna modules. Simulation models for chassis antenna cavities are critical, because they must both accurately predict antenna performance, while staying computationally reasonable. Moreover, if the chassis of electric cars, airplanes and boats are built with carbon fiber reinforced polymer, then a model for the composite laminate is required. In this paper a simple simulation model for chassis antenna cavities is developed. The carbon fiber composite material is modeled as a linear, homogeneous and isotropic conductor, and several cavity geometry details are omitted. Simulation results are in good agreement with measurements in the frequency band at 5.9 GHz for intelligent transport systems.

Pattern-reconfigurable antennas for the 2.45GHz ISM band are concealed inside a chassis antenna cavity. Three antennas are designed to reconfigure between near-optimum radiation patterns for urban scenarios by toggling between front/back and left/right radiation. The three antennas follow distinct design principles and have different gain switching capabilities. Antenna performance is evaluated based on gain pattern measurements. It is shown, that the antennas retain their reconfiguration functionality when they are placed in the chassis cavity beneath the vehicle's roof.

Vehicles increasingly communicate with their surrounding environment. They are no longer mere receptors of radio broadcasts, but actively exchange information with their surroundings. These communicative vehicles will radically change our view on transportation. They enable cooperative driving and are used as mobile access nodes for telecommunication networks - no longer just moving combustion engines. Extended radio frequency hardware is the technical basis for this increase in wireless vehicular communication. The critical part of the communication system are the antennas, as they have to be placed outside the vehicles hull and therefore become interdependent with vehicle design. This dissertation examines the influence of carbon fiber reinforced polymer on vehicular antennas and the development of an antenna cavity for vehicles. Together these findings secure enough construction space for antennas in future light-weight constructed vehicles.

Electric cars are increasingly constructed with chassis made from Carbon Fiber Reinforced Polymer (CFRP). This requires the characterization of these materials for vehicular antennas. Material samples are measured inside rectangular waveguides and the material parameters are estimated with the Nicolson-Ross-Weir method. Measurement results show, that the electric conductivity of CFRP with twill-weave and CFRP with fiber shreds on the surface are approximately isotropic in the investigated frequency range around 6 GHz. This motivates the use of recycled CFRP. Sustainable materials are in this case also optimal for antenna applications. The transition from metal to CFRP chassis influences monopole antennas, which are currently widely used in automotive applications, as these antennas use chassis parts as ground plane. Both narrowband and wideband monopole antennas are measured on ground planes manufactured from different CFRP.

A cavity for vehicular antennas is designed, manufactured, measured and evaluated. The cavity is larger than currently used roof-mounted shark-fin antenna modules and can be manufactured as part of the chassis and hidden therein. As proof that the production of such a cavity is realizable for electric cars, a prototype is built from CFRP. To show feasibility for antennas, several antennas are measured and evaluated inside the cavity. Investigated antennas include a monopole antenna and an inverted-F antenna, both manufactured as laser-structured injection molded parts; a broadband conical monopole antenna and intelligent antennas with reconfigurable radiation patterns. Detailed measurement based evaluations of the antennas inside the cavity show that the cavity concept is feasible. Influences of the cavity on the functionality of the antennas inside are also analyzed by measurement. Strong influences on the antennas occur at frequencies in the high single-digit gigahertz range, where the cavity is electrically large.

The number of antennas mounted on vehicles keeps growing. Antennas in hidden modules will replace or supplement antennas in shark-fin modules. Chassis antenna cavities were recently proposed as large antenna modules, which can be built, and concealed, inside the vehicle chassis. Recent results of multiple antennas inside a chassis antenna cavity are presented. An inverted-F antenna and a conical monopole antenna are compared, based on measurements performed in an anechoic chamber. Measurements suggest that the position of the antenna inside the cavity has a significant influence on the gain pattern. Further measurements of frequency sweeps are needed, but prior to that exchangeable cavity bases are required.

Chassis antenna cavities were recently introduced as large, hidden, antenna modules. Testing different antenna configurations inside the module would require cutting several holes into the cavity floor. Manufacturing of several prototypes is not feasible, especially for carbon-fiber reinforced polymer chassis; flexible solutions are desired. Exchangeable cavity bases for chassis antenna cavities are proposed, designed and manufactured. Antenna measurements show the feasibility of the concept.

Chassis cavities have recently been proposed as a new mounting position for vehicular antennas. Cavities can be concealed and potentially offer more space for antennas than shark-fin modules mounted on top of the roof. An antenna cavity for the front or rear edge of the vehicle roof is designed, manufactured and measured for 5.9 GHz. The cavity offers increased radiation in the horizontal plane and to angles below horizon, compared to cavities located in the roof center.

Chassis integrated antenna cavities offer ten times the space of conventional automotive roof mounted antenna modules and can be fully concealed beneath the roofline. A pattern reconfigurable antenna for 2.6 GHz LTE is measured inside an automotive chassis cavity. The antenna can be electrically reconfigured to radiate towards the front, back, left or right side of the vehicle. Measurement results show that the antenna retains this ability when being hidden beneath the roof, proving that it is possible and feasible to hide antennas utilizing pattern diversity inside chassis cavities.

A concealed vehicular carbon fiber reinforced polymer (CFRP) cavity in the roof which contains antennas is proposed, prototyped and measured. Compared to state of the art roof mounted shark-fin modules this offers significantly more room for antennas and radio frequency hardware, thus enabling a smooth transition of vehicular connectivity towards 5G. Three antennas were prototyped and embedded in the cavity: Two laser direct structured (LDS) antennas (inverted-F antenna for 2 GHz, monopole for 5.9 GHz), as well as a broadband conical monopole antenna milled from brass that characterizes the feasible frequency range from 2 to 6 GHz by measurement. It is shown that near-omnidirectional radiation from the concealed automotive antenna cavity is achievable.

Rising demand for vehicular communication and cooperative movement have led to an increase of vehicle mounted antennas. A carbon fiber reinforced polymer cavity is presented, that can be integrated into the vehicle chassis. The concealed cavity is large enough to house the anticipated antennas for present and future vehicular communication. Influence of the cavity onto antennas is demonstrated with calibrated gain measurements on the example of a 5.9 GHz monopole antenna for intelligent transportation systems. The cavities impact on antenna performance is found to be much smaller than influences of the car itself.

Carbon fiber reinforced polymer (CFRP) is measured as reflector material for millimeter waves at 60 GHz. Reflectivity is measured to characterize material anisotropy in a mono-static setup. Disc shaped material samples are rotated in steps of one degree. Four commonly employed CFRP are investigated: unidirectional fibers, plain-weave, twill-weave and fiber shreds. Results show that the unidirectional CFRP and twill-weave CFRP are anisotropic, while the remaining materials are isotropic within measurement accuracy.

Twill-weave carbon fibre reinforced polymer is measured as reflector material for electromagnetic waves at 60 GHz. The reflectivity at millimetre wavelength shows a predominant direction, which coincides with the diagonal pattern of the twill's top layer. In the remaining directions the investigated 2/2 twill-weave composite's reflectivity is almost isotropic.

A carbon fiber reinforced polymer (CFRP) laminate, with the top layer consisting of shredded fibers, is proposed and manufactured. The shredded fibers are aligned randomly on the surface to achieve a more isotropic conductivity, as is desired in antenna applications. Moreover, fiber shreds can be recycled from carbon fiber composites. Conductivity, permittivity and permeability are obtained with the Nicolson-Ross-Weir method from material samples measured inside rectangular waveguides in the frequency range of 4 to 6 GHz. The decrease in material anisotropy results in negligible influence on antennas. This is shown by measuring the proposed CFRP as ground plane material for both a narrowband wire monopole antenna for 5.9 GHz and an ultra-wideband conical monopole antenna for 1-10 GHz. For comparison, all measurements are repeated with a twill-weave CFRP.

Carbon Fiber Reinforced Polymer (CFRP) or generally Carbon Fiber Composites (CFC) are increasingly utilized in lightweight construction. Large CFRP parts such as chassis or fuselages are utilized as antenna ground planes. However, radiation characteristics of antennas designed for metal ground planes change when mounted on anisotropic composites. In this paper the influences of CFRP ground planes on the radiation characteristics of antennas in the range from 1 - 10 GHz are investigated with measurements of conical monopole antennas. Measurements show that ground planes from unidirectional CFRP severely distort radiation patterns, while the influence of woven plies is small.

The introduction of carbon-fiber composites in chassis production changed the materials in the vicinity of vehicular antennas. The two IEEE 802.11p antennas of an automotive antenna system are measured on a carbon-fiber roof and an aluminum sheet. Gain patterns are in good agreement, radiation efficiency on the carbon-fiber roof is about ten percentage points lower than on aluminum.

The impact of carbon fiber composites (CFC) as a ground plane material on antenna performance is investigated. CFC are lighweight materials that, due to their high mechanical durability, are increasingly used as chassis material for cars. Their electrical characteristics are anisotropic and dependent on the manufactured structure, which is expected to influence the radiation pattern. Simple monopole antennas for 2.45 GHz (ISM) and 5.9 GHz (ITS G5) are mounted to circular ground planes made of three diferent CFC and aluminum sheets. The influence on antenna performance is investigated with calibrated gain, return loss and the radiation pattern measurements.

Interference alignment has been proposed as a transmission technique to cancel the interference for the K-user interference channel at high signal-to-noise ratio. In the case of multiple-input multiple-output (MIMO)-transmission the interference can be aligned in a subspace of the receiver antennas. In this work we investigate the impact of outdated channel state information (CSI) due to temporal channel variations on the performance of interference alignment. Experimental transmissions of real-time precoded signals from an indoor and outdoor MIMO testbed exhibit performance degradation due to outdated CSI. Furthermore, a model is proposed and evaluated that describes the temporal channel fluctuations based on these measurements.

Interference alignment is a linear precoding technique that eliminates interference in the K-user interference channel. We present measurement results and identify the performance limiting factors that occur under real conditions. In our setup, we found the main causes of impairment to be outdated channel state information in varying channels, thermal noise at the receiver and transmit impairments. We propose a simplistic channel model that is capable of capturing these effects and allows to investigate their impact on the achievable rate.

Modern mobile communication systems are designed based on the cellular principle. The efficiency of such systems is primarily limited by interference from neighboring base stations at the cell edge. In recent years various schemes have been developed to minimize interference through base station cooperation. One such promising scheme is interference alignment (IA). Although theoretically well understood, measurement based evaluations are rare.
Interference alignment (IA) relinquishes half of the available data streams of a mobile connection to align the interference in their subspace and promises an interference free transmission on the remaining data streams. IA uses linear transmit and receive filters and requires global knowledge of the communication channels to calculate these filters. Furthermore IA requires various assumptions regarding the communication channels and the communication network. An important assumption is that the radio channels remain constant from their measurement on to the transmission of the data.
This thesis shows in a scientific, on modern communication systems based, measurement environment that practical channels allow the application of IA and presents measurements that show the impact of changing channels on the efficiency. First the theoretical basics and measurement methods of characteristic figures are summarized. Then the used measurement system, the Vienna MIMO testbed (VMTB), is specified. Differences to a commercial system are clarified and the developed software explained. Additionally the performance of IA under changing channels is quantitatively investigated with the use of mutual information.

Interference Alignment (IA) is a linear precoding scheme for the K-user interference channel with high signal to noise ratio. Ideally, interference is completely suppressed and each user is able to achieve half of the single-user multiple-input multiple-output (MIMO) degrees of freedom. We use the Vienna MIMO testbed to evaluate the feasibility of IA in realtime, in a heterogeneous outdoor to indoor and indoor to indoor scenario representative of an urban scenario. We evaluate the accuracy of alignment and provide benchmarks for typical delays in such a setup.

Molded interconnect devices (MID) allow the realization of electronic circuits on injection molded thermoplastics. MID antennas can be manufactured as part of device casings without the need for additional printed circuit boards or attachment of antennas printed on foil. Baluns, matching networks, amplifiers and connectors can be placed on the polymer in the vicinity of the antenna. A MID dipole antenna for 1 GHz is designed, manufactured and measured. A prototype of the antenna is built with laser direct structuring (LDS) on a Xantar LDS 3720 substrate. Measured return loss and calibrated gain patterns are compared to simulation results.

Recent advancements in production materials for cars replace well-known ground plane materials for vehicular antennas. Carbon-fiber composites (CFC's) replace steel as chassis material, which leads to reduced radiation efficiency. As the production processes of shark-fin antenna modules shift towards laser direct structuring (LDS), it is investigated, if antenna efficiency can be increased by the introduction of a LDS ground plane. Differences in antenna performance are presented on the example of simple LDS and wire monopole-antennas for 5.9 GHz (IEEE 802.11p, ITS G5). Gain, efficiency, return loss and the radiation patterns of an LDS design, a CFC and an aluminum ground plane are compared.

Competence-oriented education aims to teach individuals the cognitive skills required to solve specific problems and the readiness needed to apply such solutions in versatile situations. We find that competence-oriented teaching is a promising paradigm in applied courses for antennas, propagation, and wireless communications. Competence-oriented laboratory courses are easy to implement when the mechanical facilities and equipment from laboratory courses are already available at the institute. Amateur radio equipment is used so that students can work independently without risking damage to delicate equipment. In this article, we describe several methods used to modify lab courses toward competence-oriented academic teaching that we have found are popular with students and enhance their learning experience.

Simple take-home experiments are used at two universities on two continents to spark and expand student interest in the otherwise theoretical coursework in electromagnetic waves and antennas. The students obtain kits from the instructors and can do their experimental homework anytime they like, at home or in a standard undergraduate circuits lab, while combining it with theoretical exercises designed to match the experiments. Topics are covered in the order of electromagnetic wave complexity: (1) uniform plane waves in the optical frequency range with a laser pointer, gelatin and plastic polarizers; (2) frequency selective surfaces for WLAN; (3) non-uniform plane waves in VHF/UHF frequency coaxial cables; (4) quasi-TEM waves in microstrip at UHF frequencies; (5) a "cantenna"; and (6) microwave oven leakage detector.

Coins are used for size comparison in photographs. This interdisciplinary study compiles a comprehensive dataset of over one thousand instances where coins are utilized as size references in scientific publications. Employing quantitative analysis, a numismatic measurement system is uncovered that's characterized by widespread adoption and discernible conventions governing coin use. The findings are presented in this article. The analysis reveals a prototypical numismatic measurement system with widespread use and distinguishable rules how coins get used. The prevalence of coins as a size reference is within the single-digit percentage range in several technical journals. Distributions examine the number of coins per article and explore correlations of coins by number of pages, figures and photos. Text analysis reveals the authors' deliberate choice to use coins for scale and size comparison.
Coins lack many aspects of modern measurement tools. They are not used as a measurement unit unlike the meter or the inch and they don't provide a lower and upper bound on size. The dataset provides evidence that coins are used as size reference for objects with similar dimensions and are occasionally used in conjunction with other measurement tools. Coin properties other than their size are not widely used for measurement applications.
A numismatic analysis provides statistics of used currencies, denominations and mint years. Analysis reveals a trend towards larger currencies when using foreign coins, but generally coins are chosen from the first author's country. Similar items like banknotes, credit cards or jewelery are not used.
The investigation extends to the arrangement in scenes, whether they are placed next to objects or on them, the displayed sides and whether they are standing or lying horizontally. The study concludes by discussing notable outliers within the dataset.

Münzen sind als Größenreferenz in Fotos äußerst beliebt. In dieser Mitteilung beschreiben wir eine neuartige Methode, die mit Hilfe künstlicher Intelligenz (KI) Abbildungen von Münzen als Größenreferenz in Fotos einfügt. Die neuesten KI-Generatoren sind in der Lage, aus Textbeschreibungen schnell realistische Bilder von hoher Qualität zu erzeugen. Mit der vorgeschlagenen Methode ist keine physische Münze bei der Aufnahme von Fotos erforderlich. Die Münzen können nachträglich hinzugefügt werden. Außerdem zeigen wir, wie das Münzmotiv an das Objekt angepasst werden kann.

Authors of scientific articles use coins in photographs as a size reference for objects. For this purpose, coins are placed next to objects when taking the photo. In this letter we propose a novel method that uses artificial intelligence (AI) generated images of coins to provide a size reference in photos. The newest generation is able to quickly generate realistic high-quality images from textual descriptions. With the proposed method no physical coin is required while taking photos. Coins can be added to photos that contain none. Furthermore, we show how the coin motif can be matched to the object.

Coins are used as a measure of size in scientific publications. Over one hundred examples are collected. Although standardized procedures for using coins as a measure of size do not exist, use among scientists is so widespread that some form of consensus has formed in the community. Contemporary usage patterns of coins as a measure of size are analyzed qualitatively. Several rules and predictions are formulated based on this analysis.

Cellular connectivity plays an important role for the future development of automated and connected driving and intelligent traffic. An internet connection based on a 5G network can offer new services as entertainment (media streaming) or traffic information for improved navigation and cruising. Development and testing automotive antenna designs is time consuming and expensive. An open question is the evaluation of different antennas within a realistic environment. To fill this gap and facilitate optimal antenna design we introduce three scoring indicators to compare automotive antennas for cellular mobile communications and estimate their performance. This approach can be applied both to measured data and simulation results. The indicators help to make decisions on the type of integrated antenna by considering throughput as well as network coverage.

We report results from real-world millimetre wave vehicle-to-vehicle channel measurements carried out in an urban street environment, down-town Vienna, Austria. Channel measurements have been acquired with a time-domain channel sounder in the frequency band 59.75-60.25 GHz with a frequency resolution of approximately 5 MHz. We estimate the local scattering function for sequential stationarity regions in time. A multitaper estimator is used to precisely define Doppler and delay resolutions. Estimates for delay and Doppler profiles are evaluated from the local scattering function for several overtaking vehicles at a variety of speeds and for different types of vehicles. The results show that passenger cars are associated with a single Doppler trajectory, whereas larger vehicles, such as trucks, show up in the data with multiple Doppler trajectories.

We conducted drive test measurements in a live LTE 1800 MHz network to evaluate mobile network performance of User Equipments (UEs) located inside and outside a pickup truck. The measurement campaing is performed in Kosovo, starting from Prishtina to the south-western Albanian border. Knowledge of base station locations and cell load during the measurements is made available from the service provider. This is crucial to determine whether the bit rate is limited by network availability, cell load, or propagation effects. To provide reliable in-vehicle coverage, it is necessary to determine the penetration loss. In this paper, we present the first results and show that the penetration loss varies by up to 10.58 dB.