Research On Ultra-wideband Microwave Chaotic Circuits And Techniques Of Negative Resistance Enhancement

Chaotic signal is wideband, pseudorandom, noise like, so it can be widely used in secure communications, ultra-wideband communications, spread spectrum communications, chaos radar, electronic warfare and other areas. One of the research key points on chaotic circuits is the design of chaotic signal generators. The chaotic signal bandwidth is one of the most important performance indexes, which is mainly influenced by the chaotic fundamental oscillation frequency. So the primary goal in the design of chaotic circuit is to enhance the chaotic fundamental oscillation frequency and obtain ultra-wideband chaotic signal bandwidth.Chaotic Colpitts oscillator has become a hotspot in chaotic circuit research, as it can be used in microwave band. But the classic chaotic Colpitts oscillator is influenced by the low Q value and parasitic base-collector capacitance, and the chaotic fundamental oscillation frequency is only one tenth of the transition frequency of the transistor used.In this paper, the chaotic bifurcation diagram of the classical chaotic circuit has been achieved by solving the nonlinear equations. Based on the chaotic bifurcation diagram, the diference between chaotic oscillation and normal oscillation is explained in mathematical and physical methods. The parasitic capacitance influence on negative resistance is qualitatively and quantitatively analyzed by using the expressions of the negative resistance. Then the techniques of negative resistance enhancement are introduced into chaotic circuit design. A two-inductor chaotic circuit, a two-stage chaotic circuit with enhanced negative resistance and a differential chaotic circuit have been designed to enhance the chaotic oscillation frequency, bandwidth and stability.Theoretical and simulation analysis show that:1. The influence on negative resistance caused by the base-collector parasitic capacitance can be restrained with optimized two-inductor chaotic circuit.2. The two-stage chaotic circuit has been formed by adding an additional negative resistance into the one-stage chaotic circuit. And the negative resistance of the two-stage chaotic circuit is enhanced by 2 times.3. The chaotic circuit stability is enhanced in differential circuit which was designed based on the two-inductor and two-stage circuit. The stability enhancement makes the circuit testing work easier. So the chaotic oscillation frequency is up to the maximum frequency of the transistors by using the parasitic capacitors as main tank components.The novel chaotic circuits have been implemented with BFG520 transistors and 2um GaAs HBT process. Measurement results show that the fundamental oscillation frequency is up to 2.82GHz,75% higher than the highest fundamental frequency (1.60GHz) reported. The total bandwidth with continues chaotic signal spectrum is up to 9.04GHz(0.56GHz-9.60GHz), and the bandwidths with lOdB power spectrum deviation are:1.92GHz(1.28GHz-3.20GHz)、2.30GHz(3.20GHz-5.50GHz)、 3.20GHz(6.40GHz-9.60GHz).