This Master thesis examines a phenomenon that occurs in the upper polar atmosphere, namely, Polar Mesospheric Winter Echoes, or PMWEs. PMWEs are radar echoes observed by Very High Frequency Mesosphere Stratosphere Troposphere (VHF MST) radar, from altitudes of 60 to 76 km at 7 to 15 UT, in the winter months from the middle of September to the beginning of May. The aforementioned specifications are the partial results of this thesis.PMWEs are generally understood to be caused by turbulence; however, radar data indicate some rare cases where PMWEs can be created with velocities exceeding the speed of sound, which is not possible with current turbulence theory. Kirkwood et al., 2006 and Belova, Kirkwood, and Sergienko, 2013 hypothesised that infrasound could generate the necessary conditions for PMWEs with velocities equal to or exceeding the speed of sound. Observations of PMWEs presented in this thesis have been carried out by the MST radar ESRAD, located at Esrange (67 56’N, 21 04’E) near Kiruna in northern Sweden. The radar operates at 52 MHz and has been performing continuous radar observations since Dec 1996. Observations of the infrasounds presented in this thesis were carried out by a microbarometer located close to Rymdcampus in Kiruna. Access to the data is restricted, but through university administration, this master’s thesis has been granted permission to use the data for the study of PMWEs. The instrument performed continuous infrasound measurements from the 24th of May 2016 and forward. This thesis will perform a full analysis of all radar data from the 17th of Dec 1996 until the 31st of Jan 2021 to assess the altitude interval, diurnal interval and yearly interval. The data given in the first section are a result of this work. Additionally, space weather parameters relation with the occurrence of PMWEs is analysed. Space weather parameters are very important for the chemistry and conditions present in the mesosphere. It is shown thatt here is a strong relation between solar wind and PMWE occurrence, decent relation with Kp index and no to weak relation with solar particle event (SPE). Correlating space weather and PMWEs in greater detail could be the subject of other studies. Last but most interesting, microbarometer data will be analysed for days where high-speed PMWEs are detected. Because of the rarity of these high-speed PMWEs, only seven total cases were found from 24 May 2016 onward, making the analysis of the infrasound measurements very limited, and no connection was found. However, it was found that days with high-speed PMWEs had an abnormally low amount of infrasound detections, further making analysis difficult but raising questions of why. This could mean that infrasound signals might be hindered from reaching the ground on days where we have high-speed PMWEs. No further conclusions can be made, as this indicates relation but not causation. Airborne infrasound instruments could be used to detect weaker infrasound signals due to being unaffected by wind disturbance at the ground.

In eastern North America, "tree bats" (Genera: Lasiurus and Lasionycteris) are highly susceptible to collisions with wind energy turbines and are known to fly offshore during migration. This raises concern about ongoing expansion of offshore wind-energy development off the Atlantic Coast. Season, atmospheric conditions, and site-level characteristics such as local habitat features (e.g., forest coverage) have been shown to influence wind turbine collision rates by bats onshore, and similar features may be related to risk offshore. In response to rapidly developing offshore wind energy development, I assessed the factors affecting coastal and offshore presence of tree bats. I continuously gathered tree bat nightly occurrence data using stationary acoustic recorders on five structures (four lighthouses on barrier islands and one light tower offshore) off the coast of Virginia, USA, across all seasons, 2012–2019. I used generalized additive models to describe nightly tree bat occurrence in relation to multiple factors. I found that sites either indicated maternity or migratory patterns in their seasonal occurrence pattern that were associated with local roosting resources (i.e., presence of forest). Across all sites, nightly occurrence was negatively related to wind speed and positively related to temperature and visibility. Using predictive performance metrics, I concluded that the model was highly predictive for the Virginia coast. My findings were consistent with other studies—tree bat occurrence probability and presumed mortality risk to offshore wind-energy collisions is highest on nights with low wind speed, high temperature and visibility during spring and fall. The high predictive model performance I observed provides a basis for which managers, using a similar monitoring and modeling regime, could develop an effective curtailment-based mitigation strategy. Although information at fixed points is helpful for managing specific sites, large questions remain on certain aspects of tree bat migration, in part because direct evidence (i.e., tracking of individuals) has been difficult to obtain so far. For instance, patterns in fall behavior such as the timing of migration events, the existence of migratory pathways, consistencies in the direction of travel, the drivers of over-water flight, and the activity states of residents (or bats in stopover) remain unstudied in the mid-Atlantic. The recently established Motus Wildlife Tracking System, an array of ground-based receiver stations, provides a new technique to track individual bats via the ability to detect course-scale movement paths of attached very high frequency radio-tags. To reveal patterns in migration, and to understand drivers of over-water flight, I captured and radio-tagged 115 eastern red bats (Lasiurus borealis) and subsequently tracked their movements. For the bats with evidence of large movements, most traveled in a southwesterly direction whereby paths were often oriented interior toward the continental landmass rather than being oriented along the coastline. This observation challenges earlier held beliefs that bats closely follow linear landscape features, such as the coast, when migrating. I documented bats traveling across wide sections of the Chesapeake and Delaware bays confirming the species' ability to travel across large water bodies. This behavior typically occurred in the early hours of the night and during favorable flying conditions such as low wind speeds, warm temperatures, and/or during sudden increases in temperature associated with the passage of cold fronts. For bats engaging in site residency through the fall, the proportion of night-hours in which bats were in a resting state (and possibly torpor), increased with colder temperatures and the progression of the fall season. My study demonstrated that bats may be at risk to offshore wind turbine collisions off the mid-Atlantic, but that this risk might be minimal if most bats are migrating toward the interior landscape rather than following the coast. Nonetheless, if flight over large water bodies such as Chesapeake and Delaware bays is a viable proxy for over-ocean flight, then collision risk at offshore wind turbines may be somewhat linked to atmospheric, seasonal timing, or other effects, and therefore some level of predictable and manageable with mitigations options such as smart curtailment. / Master of Science / In eastern North America on the mid-Atlantic and Northeast coasts, a group of bat species named "tree bats" engage in seasonal migrations—generally shifting north in spring and south in fall. On the East coast, it is known that eastern red bats and silver-haired bats will occasionally fly over the ocean during these periods. Although this behavior is somewhat hard to explain due to their reliance on trees for day-time roosting, it raises concern conservation concerns due to the current and future rapid development of offshore wind energy turbines. This is compounded by the fact that collision rates with turbines are high for this species group in general and highest in the fall migratory season. The fall period is also when bats may be attracted to tall structures such as turbines and when most offshore flight happens. Nevertheless, bats are sensitive to atmospheric conditions such as temperature and wind speed, and other factors influence their propensity to fly (and be at risk to turbine strikes). So, understanding these drivers may aid in understanding the conditions that present the highest risk to strike at offshore wind turbines. In response to rapid offshore wind development in the Atlantic, I recorded bats in coastal Virginia, USA from 2012–2019, using acoustic monitors—devices that collect the echolocation vocalizations of bats. I found that tree bat visitation offshore or on barrier islands was associated with wind speed, temperature, visibility, and seasonality. Using statistical modeling, I developed a predictive tool to assess occurrence probabilities at varying levels of wind speed, temperature, and seasonality. Probability of occurrence and therefore assumed risk to collision was highest on high temperature and visibility nights, low wind speed nights, and during the spring and fall seasons. Therefore, I suggest a similar modeling regime could be used to predict the occurrence of bats at offshore wind sites to inform potential mitigation efforts. Next, I attempted to answer broader questions about tree bat migratory behavior such as attempting to identify migratory pathways throughout the mid-Atlantic. The Motus Wildlife Tracking System gives researchers the ability to directly track individuals over long-distances with radio-transmitters and ground-based receiver stations. Using Motus, I captured and radio-tagged >100 tree bats, which were of majority eastern red bats and tracked their movements throughout the mid-Atlantic region. I found that movements were not oriented along the coastline, which challenged previously held beliefs that bats use the coast during migration. Tree bats also traversed large bodies of water, the Chesapeake and Delaware bays, confirming the ability for this group to fly over-water. Through statistical modeling, I found that these over-water bouts were early in the night and related to advantageous flying conditions such as low wind speeds, high temperatures, and during periods of sudden temperature increase (which could be linked to the passage of cold weather fronts). Offshore collision risk to tree bats may be somewhat minimal if most bats orient inland, rather than coastal for their migration movement. Nevertheless, for those bats that do fly over the ocean, if crossing large waterbodies is a viable proxy for over-ocean movement, then this behavior is linked to multiple factors, of which can be used to predict occurrences and even potentially predict and manage risk to collision.

Within the military there is great need for reliable communication between vehicles. During the planning and construction of a military RIB, Rigid-hulled Inflatable Boat, it is important to design an efficient antenna system that does not deteriorate out of disorder. It must also be ensured that the antennas transmitted power does not stay in the RIB boat. We have been given assignment to model and simulate a proposed antenna system and assess which tool is best suitable for the task. To analyze the antenna system we will look at the radiated electrical field together with the reflectionand EMC properties. The tool that we choose to use is a software called EMPro produced by Keysight Technologies. In this program we will create 3Dstructures for each individual object, the boat, the three antennas and the seawater. It’s also important to include each objects properties concerning material, so that they correctly reflect the reality. We are covering a broad spectrum with our antennas reaching from 1.6-30MHz, 30-88MHz and 100512MHz. The resulting simulation verifies that electromagnetic field would be powerful enough and that the antennas would not affect each other with the proposed placement. We could also confirm that our antennas reflected an inordinate amount of power but with cause that our models were not an exact replica of the antenna. The software EMPro is a suitable tool for this kind of projects concerning modeling and simulating antenna systems.Within the military there is great need for reliable communication between vehicles. During the planning and construction of a military RIB, Rigid-hulled Inflatable Boat, it is important to design an efficient antenna system that does not deteriorate out of disorder. It must also be ensured that the antennas transmitted power does not stay in the RIB boat. We have been given assignment to model and simulate a proposed antenna system and assess which tool is best suitable for the task. To analyze the antenna system we will look at the radiated electrical field together with the reflectionand EMC properties. The tool that we choose to use is a software called EMPro produced by Keysight Technologies. In this program we will create 3Dstructures for each individual object, the boat, the three antennas and the seawater. It’s also important to include each objects properties concerning material, so that they correctly reflect the reality. We are covering a broad spectrum with our antennas reaching from 1.6-30MHz, 30-88MHz and 100512MHz. The resulting simulation verifies that electromagnetic field would be powerful enough and that the antennas would not affect each other with the proposed placement. We could also confirm that our antennas reflected an inordinate amount of power but with cause that our models were not an exact replica of the antenna. The software EMPro is a suitable tool for this kind of projects concerning modeling and simulating antenna systems. / Inom militären finns stort behov av pålitlig kommunikation mellan fordon. Vid konstruktion av ett småfartyg i militärtoch bevakningssyfte är det viktigt att designa ett välfungerande antennsystem som inte försämras utav störningar, det ska även ses till att antennernas utsända effekt inte fastnar i småfartyget. Vi har fått en ritning av hur antennplaceringen är planerad, denna rapport går ut på att verifiera dess funktionalitet samt hitta en mjukvara som kan användas för att verifiera olika antennsystem. För att bedöma antennsystemet kommer denna rapport att undersöka att dess elektriska fält samt reflektionsoch EMC egenskaper, en uppgift som kan lösas med programvaran EMPro (Keysight). I programvaran skapas en 3Dstruktur som innehåller småfartyget, dess 3 stycken antenner samt omfattande havsvatten. Här tas hänsyn till objektens materialegenskaper, antennernas jordning samt de frekvenser antennerna arbetar på, 1.6-30MHz, 30-88MHz samt 100-512MHz. Simulering av systemet gav positiva resultat kring antennsystemets elektromagnetiskafält, antennerna kommer inte heller att störa varandra. Antennerna som vi har modellerat reflekterar orimligt mycket effekt, detta bortser vi från då vi inte haft tillgång till exakt avbildning av antennerna. EMPro är ett verktyg som är lämpligt att använda i detta samt liknande projekt. Dock krävs det att en kraftig dator finns tillgänglig då simuleringar av stora antennsystem baseras på stora uträkningar, som generellt tar lång tid.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: A well-known problem with FM-CW radar systems is the leakage of transmitter power into the receiver which leads to the making of close-in targets, and can severely limit the system dynamic range performance. This thesis considers two solutions to this radar system problem for a low frequency radar operating in the VHF band. The first method to suppress coupling is using separate transmit and receive antennas designed in such a way as to reduce coupling between them. The second is to design a negative feedback loop as part of the radar receiver where the feedback loop adaptively reduces the amount of transmitter leakage through to the receiver. This project details the realisation of these two solutions. A number of antenna designs are modelled in software and simulated to determine their characteristics of which the transmit-to-receive coupling is the key parameter. As no low coupling configuration could be found a simple configuration is chosen and practical measurements are taken. These antennas are then used in the radar system that is to be built. An FM-CW radar system is designed and simulated using software with a negative feedback loop being designed and implemented into the radar simulation. A practical radar system is then made inclusive of the feedback loop. Measurements are then taken to determine the efficacy of the feedback loop. / AFRIKAANSE OPSOMMING: ʼn Bekende probleem met FM-CW radar stelsels is die lekkasie van versender krag tot in die ontvanger wat lei tot die maak van nabye teikens en kan die stelsel se dinamiese sendbereik steng beperk. Hierdie tesis oorweeg twee oplossings tot hierdie probleem vir ʼn lae frekwensie radar wat in die VHF band werk. Die eerste metode wat na gekyk word om die koppeling te onderdruk is om die twee antennas van die radar stelsel so te ontwerp sodat die hoeveelheid koppeling tussen hulle verminder is. Die tweede is om ʼn negatiewe terugvoerlus as deel van die ontvanger te ontwerp. Hierdie terugvoerlus sal die versender lekkasie sein aanpassend in die ontvanger verminder. In hierdie projek word die realisering van bogenoemde oplossings uiteengeset. ʼn Paar verskillende antenna ontwerpe word gemodelleer in sagteware en word gesimuleer om hul karakteristieke te bepaal. Die belangrikste van hierdie faktore is die versender na ontvanger koppeling. Sienend dat geen ontwerp met ʼn lae genoeg koppeling gevind kon word nie, is ʼn eenvoudige ontwerp gekies en praktiese metings daarvan geneem. Hierdie antennas word dan gebruik in die radar stelsel wat gebou sal word. ʼn FM-CW radar stelsel word ontwerp en gesimuleer in sagteware. Die negatiewe terugvoerlus word ook ontwerp en geïmplementeer in die radar simulasie. ʼn Praktiese radar stelsel word dan gemaak insluitend die terugvoerlus. Metings word dan geneem om die effektiwiteit daarvan te bepaal.

[pt] Este trabalho descreve o desenvolvimento completo de um Amplificador de Potência de RF para Transceptores Multibanda. Em sua etapa inicial mostra um apanhado geral da teoria de todos os parâmetros relevantes para a medida de desempenho desses dispositivos, como potência, ganho e parâmetros de não linearidades. Em seguida são expostas as teorias básicas para o entendimento dos mecanismos para extração da máxima potência de um transistor, focando nos transistores de efeito de campo FET, incluindo a caracterização para regimes de alta potência. São apresentados os modos de operação de um amplificador de potência, focando nos chamados modos clássicos, dado que esses modos são convenientes para operação em banda larga. Para a correta operação de qualquer dispositivo que apresente ganho, a análise de estabilidade é apresentada com o procedimento de estabilização de transistores. A partir de todo o apanhado teórico, é desenvolvida uma metodologia de projeto de amplificadores de potência utilizando a ferramenta de simulação computacional Advanced Design System. Então, após toda a modelagem do amplificador, a construção e medidas são realizadas e boa concordância com a simulação foi obtida. / [en] This work describes the full development of a RF Power Amplifier for Multiband Transceivers. In its initial stage shows an overview of the theory of all relevant parameters to measure the performance of these devices, like power, gain and nonlinearity parameters. Then it exposes the basic theories for the understanding of the mechanisms for extracting the maximum power of a transistor, focusing on field effect transistors FET, including characterization for regimes of high power. It presents the modes of operation of a power amplifier, focusing on so-called classical modes, since these modes are suitable for broadband operation. For proper operation of any device that presents gain, the stability analysis is presented with the stabilization procedure of transistors. From all theoretical basis, is developed a design methodology of power amplifiers using the computational simulation tool Advanced Design System. So after all the amp modeling, construction and measurements are performed and good agreement was obtained with the simulation.

Doppler radar wind profilers are already widely used to measure atmospheric winds throughout the free troposphere and stratosphere. Several methods have been developed to quantify atmospheric turbulence with such radars, but to date they have remained largely un-tested; this thesis presents the first comprehensive validation of one such method. Conventional in-situ measurements of turbulence have been concentrated in the surface layer, with some aircraft and balloon platforms measuring at higher altitudes on a case study basis. Radars offer the opportunity to measure turbulence near continuously, and at a range of altitudes, to provide the first long term observations of atmospheric turbulence above the surface layer. Two radars were used in this study, a Mesosphere-Stratosphere-Troposphere (MST) radar, at Capel Dewi, West Wales, and the Facility for Ground Based Atmospheric Measurements (FGAM) mobile boundary layer profiler. In-situ measurements were made using aircraft and tethered-balloon borne turbulence probes. The spectral width method was chosen for detailed testing, which uses the width of a radar's Doppler spectrum as a measure of atmospheric velocity variance. Broader Doppler spectra indicate stronger turbulence. To obtain Gaussian Doppler spectra (a requirement of the spectral width method), combination of between five and seven consecutive spectra was required. Individual MST spectra were particularly non-Gaussian, because of the sparse nature of turbulence at its observation altitudes. The width of Gaussian fits to the Doppler spectrum were compared to those from the `raw' spectrum, to ensure that non-atmospheric signals were not measured. Corrections for non-turbulent broadening, such as beam broadening, and signal processing, were investigated. Shear broadening was found to be small, and the errors in its calculation large, so no corrections for wind shear were applied. Beam broadening was found to be the dominant broadening contribution, and also contributed the largest uncertainty to spectral widths. Corrected spectral widths were found to correlate with aircraft measurements for both radars. Observing spectral widths over time periods of 40 and 60 minutes for the boundary layer profiler and MST radar respectively, gave the best measure of turbulence intensity and variability. Median spectral widths gave the best average over that period, with two-sigma limits (where sigma is the standard deviation of spectral widths) giving the best representation of the variability in turbulence. Turbulent kinetic energies were derived from spectral widths; typical boundary layer values were 0.13 m 2.s (-2) with a two-sigma range of 0.04-0.25 m 2.s (-2), and peaked at 0.21 m 2.s (-2) with a two-sigma range of 0.08-0.61 m 2.s (-2). Turbulent kinetic energy dissipation rates were also calculated from spectral widths, requiring radiosonde measurements of atmospheric stability. Dissipation rates compared well width aircraft measurements, reaching peaks of 1x10 (-3) m 2.s (-3) within 200 m of the ground, and decreasing to 1-2x10 (-5) m 2.s (-3) near the boundary layer capping inversion. Typical boundary layer values were between 1-3x10 (-4) m 2.s (-3). Those values are in close agreement with dissipation rates from previous studies.

This term paper is the second part of the dissertation FM RDS signal processing using FPGAs. In the first half of the work is processed the information needed before the actual design and implementation. These can be divided into three themes. The first theme is the received signal VHF / FM + RDS, the second one handles the problem of software radio and last topic concerns FPGAs. The second half deals with the solution implementation and receiver radio VHF / FM and bitrate optional RDS to digital form and its implementation on FPGA. This section also includes the measurement of results.

The aim of this work is to design a microprocessor-controlled multimode VHF radio can receive AM, FM and DAB. The first step is to become familiar with digital radio broadcasting DAB and RDS. Then we can proceed to the design of the receiver circuit solution using modern component base. Next it is necessary to write utility software and construct a prototype of receiver, verify its functionality and parameters. The result of the work is the multi-mode VHF broadcasting receiver controlled using touch screen display and supported by web management.

The common objective of this project is implementation of software defined radio (SDR) into FPGA. The text contains review and comparison of several hardware concepts intended for SDRs implementation then the methods for digital implementation of various components of radios as the filters, mixers and others are mentioned. Part of the text introduces used hardware platform and describes software support for designing, simulations and implementation into hardware. Significant part of project describes complex of external hardware components as filter, amplifier and control panel designed and built within the project realization. But the main part of project demonstrates design of the software solution of radio receiver. There is specified architecture of radio for FM broadcast receiving, next the more complex systems with carrier recovery algorithm are presented. These systems are able to work with AM, BPSK and QPSK modulations. It is possible to implement all these receivers into hardware and verify their operation. The practical laboratory theme has been outlined within the project run.