Microwave Chaotic Circuit And Its Applications In Communications

Chaotic communication has recently attracted great interests because of its potential applications in communications. This dissertation addresses the three main issues in chaotic communication: design and implementation of chaotic signal generator operating in microwave band, synchronization of chaotic circuits and new methods of applying chaos to communications.In order to design chaotic oscillator operating in microwave regime to widen the bandwidth of the generated chaotic signal, two schemes are tried in this dissertation. The first scheme is to replace the operational amplifier based nonlinear negative resistance (NDR) in classic Chua's circuit with a high-speed tunnel diode to improve the speed of the NDR and thus improve the oscillation frequency (chapter 2). The tunnel diode based Chua's circuit is analyzed by mathematical evaluation and numeric simulations. The second scheme is to use Colpitts circuit to generate microwave chaotic signals (chapter 3). Based on the mathematic analysis of the Colpitts circuit model, this dissertation proposes a method to determine the parameter expressions of the main circuit components, given the fundamental frequency of the chaotic oscillation, and conducts circuit simulations to verify the circuit parameter expressions. Further more, circuit experiments were conducted on chaotic Colpitts oscillation operating in microwave regime using two types of Philips broadband bipolar junction transistors, namely BFG520XR and BFG425W. Chaotic oscillation can be observed in Colpitts circuit with the highest fundamental frequency of 1.6 GHz, which is the highest one reported till now to the best of our knowledge.Synchronization of chaotic Colpitts circuit is studied in the second part of this dissertation (chapter 4). For the synchronization of one-way coupled chaotic Colpitts circuit, based on a generic criterion of global chaos synchronization, the sufficient condition for the coupling parameters is derived to obtain synchronization in two linear coupled unidirectional Colpitts circuits. Chaos synchronization performances of Colpitts circuit are compared when thelinear error feedback synchronization scheme and the PC synchronization scheme are used. Researches on adaptive synchronization of chaotic Colpitts circuit are carried out when there exist circuit parameter mismatches between the driver and the response system and channel distortions are considered. Besides of the study of synchronization in one pair Colpitts circuit, dual synchronization of chaotic Colpitts circuit is also investigated in this dissertation. It is discovered for the first time that dual synchronization can be achieved in two pairs of chaotic circuits with totally different circuit structures (one pair of Colpitts circuits and one pair of Chua's circuits).In the third part of this dissertation, chaotic communication based on dual synchronization of chaotic Colpitts circuits is investigated. After introducing and analyzing a "three-channel" communication scheme using dual synchronization, this dissertation proposes a novel "single-channel" featured digital secure communication system based on dual synchronization of chaos between Colpitts circuits. In this system the usage of channel resources is greatly reduced and the security performance is obtained from both protocol layer and physical layer. The bit error rate (BER) performance of this system is demonstrated by simulations.