Radiofrequency broadband tunable oscillator based on non-Foster impedance/admittance

Objašnjen je osnovni princip rada oscilatora, uvjet samopobude i analizirana posebnost oscilatora temeljenog na nefosterovskoj impedanciji/admitanciji. Razjašnjene su temeljne karakteristike sklopova za dobivanje negativne impedancije te provedene simulacije S-parametara, tranzijentna analiza, simulacija velikog signala te AC analiza. Sve simulacije sklopova provedene su u programskom paketu ADS s ultra-brzim operacijskim pojačalom THS4304. Također, diskutiran je utjecaj nelinearnih efekata na svojstva negativne impedancije. Dani su temeljni zaključci u vezi negativnih pretvornika impedancije N-tipa i S-tipa. Projektirana su i međusobno komparirana tri različita oscilatora temeljena na nefosterovskoj impedanciji te analizirani njihovi valni oblici, procesi utitravanja, spektri i izlazna snaga. Razmatrani su načini ugađanja frekvencije te ovisnost frekvencije o teretu i izvedbi negativnog pretvornika impedancije. Serijski spoj kapaciteta i otpora ili induktiviteta i otpora simulirao je kao teret električki kratku antenu, a rezonantni sklop omogućio promjenu frekvencije osciliranja u širem frekvencijskom opsegu. Na koncu su obavljena mjerenja na praktično ostvarenim sklopovima i uspoređeni rezultati sa simulacijama.Basic working principles of oscillator and conditions for oscillation were explained and specialty of oscillator based on non-Foster impedance/admittance was analised. Also, basic characteristics of circuits designed to get negative impedance were explained together with S-parameter simulations, transient simulations, large signal and AC simulations. All before mentioned simulations were performed with program ADS and based on high-speed operational amplifier THS4304. Moreover, influence of nonlinear effects on changing negative impedance characterictics was discussed. Some basic conclusions were given about short circuit stable and open circuit stable types of negative impedance converter. Three different designs of oscillator based on non-Foster impedance were made and compared as well as their waveforms, oscillation process, spectrum and output power were analised. Tuning of frequency and frequency dependance considering the load and negative impedance converter design was also discussed. Electrically short antenna as the load was simulated with serial combination of resistance and capacitance/inductance and resonant circuit enabled frequency tuning within wide frequency range. In the end measurements were made on practical circuits and compared with simulation results