Development of terahertz vacuum electronics for array receivers

Heterodyne array receivers are employed in radio astronomy to reduce the observing time needed for mapping extended sources. One of the main factors limiting the amount of pixels in terahertz receivers is the difficulty of generating a sufficient amount of local oscillator power. Another challenge is efficient diplexing and coupling of local oscillator and signal power to the detectors. These problems are attacked in this dissertation by proposing the application of two vacuum electronic terahertz amplifier types for the amplification of the LO-signal and by introducing a new method for finding the defects in a quasioptical diplexer. A traveling wave tube (TWT) design based on a square helix slow wave structure (SWS) at 825 GHz is introduced. It exhibits a simulated small-signal gain of 18.3 dB and a 3-dB bandwidth of 69 GHz. In order to generate LO-power at even higher frequencies, the operation of an 850-GHz square helix TWT as a frequency doubler has been studied. A simulated conversion efficiency of 7% to 1700 GHz, comparable with the state-of-art solid-state doublers, has been achieved for an input power of 25 mW. The other amplifier type discussed in this work is a 1-THz cascade backward wave amplifier based on a double corrugated waveguide SWS. Specifically, three input/output coupler types between a rectangular waveguide and the SWS are presented. The structures have been realized with microfabrication, and the results of loss measurements at 1 THz will be shown. Diplexing of the LO- and signal beams is often performed with a Martin-Puplett interferometer. Misalignment and deformation of the quasioptical components causes the polarization state of the output signal to be incorrect, which leads to coupling losses. A ray-tracing program has been developed for studying the influence of such defects. The measurement results of the diplexer of a multi-pixel terahertz receiver operated at the APEX telescope have been analyzed with the program, and the results are presented. The program allows the quasioptical configuration of the diplexer to be corrected in order to obtain higher receiver sensitivity

Jäähdytetty 90 GHz:n VLBI-vastaanottimen etupää

A cooled 90 GHz VLBI-receiver front end is discussed in this thesis. Very Long Baseline Interferometry (VLBI) is a method in which the signals received by several radiotelescopes, located even on different continents, measuring the same object are combined in order to achieve a higher angular resolution and imaging capability. The focus of this work is on the design of passive waveguide components. A corrugated feed horn, a polariser, a directional coupler, a power divider and a band-pass filter were designed. Their simulated properties are presented, and from the part of the power divider and the band-pass filter, the prototypes of which were available before the writing of this thesis, a comparison to actual devices is carried out. The prototypes were measured at room temperature. The heart of the front end is two lownoise preamplifiers provided by DA-Design Ltd. They are based on indium-phosphide high electron mobility transistors (InP HEMTs), the structure and operating principle of which are reviewed. A measurement procedure for obtaining the gain and noise characteristics at room and cryogenic temperatures is described, and the measurement results are presented from the part of one amplifier. A 20 percent operating bandwidth was set as a goal. Expect for the polariser, the simulated performance of all the components was satisfactory for such a bandwidth. Axial ratio and isolation requirements of 0.5 dB and 30 dB limited the relative bandwidth of the polariser to about 13 percent. The properties of the prototype power divider followed the simulations closely, the power split being equal and the return loss better than 18 dB. Even though the width of the pass-band of the prototype filter was the desired one, the pass-band had shifted about 1 GHz towards lower frequencies. The average insertion loss was 0.8 dB. The average noise temperature and gain of the low-noise preamplifier were 60 K and 53 dB at a temperature of 20 K.Tässä työssä käsitellään 90 GHz:n VLBI-vastaanottimen jäähdytettyä etupäätä. Pitkäkanta interferometria, eli Very Long Baseline Interferometry (VLBI), on menetelmä, jossa useiden, jopa eri mantereilla sijaitsevien, samaa kohdetta havaitsevien radioteleskooppien mittaustulokset yhdistetään suuremman erotuskyvyn ja kuvantamisominaisuuden saavuttamiseksi. Työn painopiste on passiivisten aaltoputkikomponenttien suunnittelussa. Suunniteltuja komponentteja ovat korrugoitu syöttötorvi, polarisaattori, suuntakytkin, tehonjakaja ja kaistanpäästösuodatin. Komponenttien simuloidut ominaisuudet esitetään, ja koska tehonjakajasta ja suodattimesta ehdittiin teettää prototyypit ennen työn valmistumista, niistä saatuja mittaustuloksia verrataan simuloituihin. Prototyypit mitattiin huoneenlämpötilassa. Kaksi DA-Design Oy:n toimittamaa vähäkohinaista esivahvistinta muodostaa etupään ytimen. Ne perustuvat korkean elektroniliikkuvuuden transistoreihin, joiden substraattina on käytetty indium-fosfidia (indium-phosphide high electron mobility transistor, InP HEMT). Transistorien rakenne ja toimintaperiaate käydään pääpiireittäin läpi, ja mittausmenetelmä sekä huoneenlämpötilassa olevan että 20 kelviniin jäähdytetyn vahvistimen kohinalämpötilan ja vahvistuksen selvittämiseksi kuvataan. Mittaustulokset esitetään toisen vahvistimen osalta. Kahdenkymmenen prosentin toimintakaista asetettiin tavoitteeksi. Simuloinnit osoittivat kaikkien komponenttien täyttävän tavoitteen polarisaattoria lukuun ottamatta. Sen toimintakaista rajoittui noin 13 prosenttiin 0.5 dB:n akselisuhde- ja 30 dB:n isolaatiovaatimuksen takia. Prototyyppitehonjakajan mitatut ominaisuudet vastasivat varsin hyvin simuloituja: teho jakaantui tasan ja paluuvaimennus oli enemmän kuin 18 dB:ä. Vaikka prototyyppisuodattimen mitattu kaistanleveys oli haluttu, päästökaista oli siirtynyt noin 1 GHz:n verran alemmille taajuuksille. Keskimääräinen väliinkytkemisvaimennus oli 0.8 dB. Jäähdytetyn esivahvistimen keskimääräiseksi kohinalämpötilaksi mitattiin 60 K:iä ja vahvistukseksi 53 dB:ä

37 GHz observations of a large sample of BL Lacertae objects

We present 37 GHz data obtained at Metsahovi Radio Observatory in 2001 December - 2005 April for a large sample of BL Lacertae objects. We also report the mean variability indices and radio spectral indices in frequency intervals 5 - 37 GHz and 37 - 90 GHz. Approximately 34 % of the sample was detected at 37 GHz, 136 BL Lacertae objects in all. A large majority of the detected sources were low-energy BL Lacs (LBLs). The variability index values of the sample were diverse, the mean fractional variability of the sample being \Delta S_2 = 0.31. The spectral indices also varied widely, but the average radio spectrum of the sample sources is flat. Our observations show that many of the high-energy BL Lacs (HBL), which are usually considered radio-quiet, can at times be detected at 37 GHz.Comment: 12 pages, 5 figures + 5 tables. Published in Astronomical Journa

Väkivaltatyö Itä-Suomessa - Väistö-hankkeen arviointi

Väkivaltatyön käytännön toimintatapojen kehittäminen Itä-Suomessa-hankkeen (Väisto) tavoitteena oli vahvistaa perhe- ja lähisuhdeväkivallan ehkäisyn ja ongelmiin puuttumisen rakenteita ja väkivaltatyön osaamista. Väistö-hanketta on toteutettu hankeperheessä, johon on kuulunut VIOLA ry:n Saumuri-hanke ja Rikosuhripäivystyksen Orava-hanke. Hankkeen toteuttamisen selkeitä vahvuuksia ovat olleet koulutukset, jotka ovat tavoittaneet laajan joukon hankealueen sosiaali- ja terveysalan ammattilaisia. Koulutusten myötä väkivaltaan liittyvä osaaminen on lisääntynyt, samoin väkivallasta kysymiseen tarkoitettujen työvälineiden käyttö on lisääntynyt. Hankealueella luotiin kaksi toisistaan poikkeavaa toimintamallia, joilla on yhteiset ja jaetut tavoitteet. Väistö-hankkeen ja siinä luotujen käytäntöjen tärkeitä vahvuuksia ovat olleet yksinkertaiset ja selkeät hoitopolut molemmilla toiminta-alueilla, palveluihin hakeutumisen matala kynnys, hankkeen vetäjien vahva sisällöllinen asiantuntemus ja hankkeen tavoitteita tukeva organisaatiokulttuuri ja ilmapiiri. Väistön myötä syntyneet toimintamallit ovat käytännössä testattuja ja hyviksi todettuja

Low noise amplifiers for MetOp-SG

We present low-noise amplifiers (LNA) that have been developed in the framework of two pre-qualification ESA projects for frequencies between 54 and 229 GHz for the METOP-SG satellite program. The main goal of these satellites is water vapor detection in atmospheric science and weather forecasting which advances the current state of the art for the metamorphic high electron mobility transistor (mHEMT) technology. The MMIC amplifiers are based on the In0.52Al0.48As/In0.8Ga0.2As/In0.53Ga0.47As heterostructure and utilize transistors with a gate length of 50 nm. On-wafer measurements will be presented for all frequency bands as well as results of packaged LNAs

Government steering Beyond 2020 : From Regulatory and Resource Management to Systems navigation

The Steering2020 project provides an overview of the development and current state of Finnish state governance and strengthens the discussion on the possibilities of systemic governance. The analysis identifies enablers and barriers in the transition to more phenomenon-based steering. The more systems-based form of future steering and anticipatory governance is called systems navigation. The project is based on complexity- and systems-theoretical interpretations of anticipatory governance. From the perspective of complexity thinking, the challenges and opportunities of system navigation are not in the characteristics of institutions and actors themselves, rather in the relationships between them. Systems navigation is a structure and process of systemic steering that emerges and guides interaction, with an emphasis on a humble and forward-looking approach to governance and decision-making, as well as systemic trust and learning. The Covid-19 crisis has provided an exceptional frame of reference for analysing the policy tools and instruments of systems steering in crisis situations. In part, the exceptional situation has reinforced the perceived need for a more systemic approach to steering, in part it has highlighted the longing for clear competencies and less complexity. Multilevel systems steering does not represent mainstream. It is therefore important to draw lessons and learn from examples of cultural change on international, regional and local level, as well as to support systemic trust and adaptation, and to introduce incentives to reform guidance when needed.This publication is part of the implementation of the Government Plan for Analysis, Assessment and Research. (tietokayttoon.fi) The content is the responsibility of the producers of the information and does not necessarily represent the view of the Government