Title Non-Foster radio frequency source Title (croatian) Nefosterovski radiofrekvencijski izvor Author Aleksandar Kiričenko Mentor Silvio Hrabar (mentor)Committee member Silvio Hrabar (član povjerenstva)Granter University of Zagreb Defense date and country 2020, Croatia Scientific / art field, TECHNICAL SCIENCES Universal decimal classificationUDC ) 621.3 - Electrical engineering Abstract This research focuses on broadband non-Foster matching of electrically small antennas, particularly in the transmitter applications. As a starting point, an effort was made to evaluate, theoretically and experimentally, the extent of advantages offered by non-Foster matching, if the stability problem (which is inherent for all non-Foster circuits) were not present. A linear, quadrature non-Foster-like circuit has been developed, which closely mimics the behaviour of non-Foster matched transmitter system, with the advantage that it does not suffer from stability issues. The behaviour of such a system is very similar to the behaviour of a native non-Foster matched transmitter, under the same conditions. The antenna reactance cancellation effect was confirmed experimentally and the radiated power was found to be constant within the wide frequency range. However, the efficiency of energy transfer to the antenna with this technique was found to be modest. Another, more versatile, linear non-Foster-like transmitter-antenna system was developed based on an RF current source that mimics open-circuit-stable non-Foster element behaviour. This principle of operation was verified through the measurements on a demonstrator and the results were consistent with theory and simulations. Both of the proposed linear non-Foster-like systems comprise linear amplifiers that generally exhibit low efficiency that is further deteriorated when driving highly reactive loads such as small antenna. Therefore, the solutions based on non-linear, discrete-time circuits were considered and investigated. Several non-linear non-Foster-like transmitter-antenna topologies were proposed, utilising voltage supply tracking, pulse width modulation and current tracking operation principles. The representative solution was practically verified by measurements on demonstrator model showing improvement of efficiency compared to linear non-Foster-like transmitter system, as well as further advantages over classic non-Foster matching.
Abstract (croatian) Ovo istraživanje usredotočeno je na nefosterovsko prilagođenje električki kratkih antena posebno za odašiljačku primjenu. Kao polazište, pokušalo se teoretski i eksperimentalno utvrditi prednosti koje bi nudila tehnika nefosterovskog prilagođenja, u slučaju kada problem stabilnosti (koji je svojstven svim nenfosterovskim mrežama) ne bi bio prisutan. U tu svrhu razvijen je linearni kvadraturni sustav odašiljač-antena, koji vjerno oponaša funkciju klasičnog nefosterovski prilagođenog odašiljačkog sustava, s bitnom razlikom da ne sadrži pozitivnu povratnu vezu, koja je osnovni uzrok problema stabilnosti kod nefosterovskih elemenata. Ponašanje takvog sustava je vrlo slično ponašanju izvornog nefosterovskog odašiljačkog sustava. Simulacijama i eksperimentalno potvrđen je efekt poništenja reaktancije antene, što rezultira jednakom izračenjem snagom u širokom rasponu frekvencija. Međutim, učinkovitost prijenosa energije na antenu ovakvim sustavom ostaje i dalje skromna. Slijedeći, svestraniji linearni nefosterovski sustav odašiljač-antena razvijen je na temelju radiofrekvencijskog strujnog izvora koji oponaša nefosterovski element stabilan pri otvorenom kraju (OCS). Ispravnost ovog pristupa eksperimentalno je potvrđena, a rezultati su u skladu s teorijom i simulacijama. Oba predložena linearna sustava koji oponašaju nefosterovsko prilagođenje sadrže linearna pojačala koja su poznata kao nisko učinkovita, a što se dodatno pogoršava pri opterećenju vrlo reaktivnim trošilima, poput kratke antene. Stoga su razmatrana i istražena rješenja temeljena na nelinearnim sklopovima koji rade u diskretnom vremenu. Predloženo je i simulacijama evaluirano nekoliko nelinearnih rješenja sustava odašiljač-antena u sklopnom načinu rada: varijanta s adaptibilnim naponom napajanja, varijanta s pulsno-širinskom modulacijom i varijanta s praćenjem struje. Reprezentativno rješenje između predloženih praktično je verificirano mjerenjima na prototipu. Rezultati su pokazali poboljšanje učinkovitosti u usporedbi s linearnim, nefosterovski inspiriranim sustavom odašiljač-antena kao i nekoliko drugih prednosti u odnosu na klasično nefosterovsko prilagođenje.
Keywords
small antenna
transmitter
non-Foster
reactance
power
matching
efficiency
non-linear
current tracking
Keywords (croatian)
kratka antena
nefosterovski
odašiljač
snaga
prilagođenje
efikasnost
linearno
nelinearno
sklopni
tranzistorska sklopka
pojačalo
praćenje struje
negativni pretvornik imitancije
Language english URN:NBN urn:nbn:hr:168:019651 Study programme Title: Doctoral study programme "Electrical Engineering and Computing" Catalog URL http://lib.fer.hr/cgi-bin/koha/opac-detail.pl?biblionumber=52325 Type of resource Text Extent xvi, 173 str. File origin Born digital Access conditions Closed access Terms of use Created on 2022-03-09 13:54:16
