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Abstract
In this paper, the mathematic model of Colpitts oscillator is illustrated and the expressions for the main circuit parameters are derived, with which chaotic oscillation can be established. Experimental researches were conducted on the implementations of chaotic Colpitts oscillator using two types of broadband bipolar junction transistors (BJTs), namely BFG520XR and BFG425W with corresponding threshold frequency of 9 GHz and 25 GHz. Experimental results indicate that, chaotic oscillation can be obtained in a wide frequency regime in microwave band. When using BFG425W in the Colpitts circuit, the highest fundamental frequency of the chaotic oscillation can be about 1.6 GHz, and the harmonics observed with Agilent PSA/ESA Spectrum Analyzer are noticeable as far as 12 GHz, which is the highest one reported so far. Several typical applications using such chaotic oscillators are also presented at the end of this paper.