Study On Active Wideband Miniaturized Antennas

In recent years,with the continuous development of wireless technology,people's demand for communications equipment is increasing,and the study of wideband miniaturized antenna is particularly important.Traditional electrically small antennas are difficult to achieve wideband miniaturization because of the limitation of bandwidth gain volume constraint theory.The non-foster circuit using the negative impedance converter can effectively improve the bandwidth,low gain and large volume of the conventional antenna,and is beneficial to realize wideband miniaturization of the antenna.In this paper,an active wideband miniaturized antenna based on non-foster matching circuit is studied,and the main work is as follows:Firstly,the non-foster circuit based on the transistor S parameter model and the practical non-foster circuit are designed.The simulation results show that two kinds of circuits can generate negative capacitance in the 100MHz-600 MHz frequency range,their reactance characteristics are opposite to the positive capacitance,and change with the negative slope of frequency.After that,the influence of the main parameters of the circuit on the simulation results is analyzed.Finally,based on the stable non-foster circuit,the simulation proves that the reactance of the negative capacitance produced by the circuit can effectively cancel the reactance of the positive capacitance.Secondly,an active wideband miniaturized antenna based on non-foster matching circuit is designed.The active antenna radiator is monopole antenna,its height is 120 mm.Firstly,the impedance parameters and S parameters of the antenna are extracted by software HFSS simulation,then the equivalent circuit model of the antenna is established according to the extracted parameters,and a stable non-foster active matching circuit is designed.The simulation results show that the circuit can generate negative capacitance and cancel the large reactance of monopole antenna,thus improving the imaginary part characteristic of the input impedance of the antenna.Finally,a passive matching network is designed,and the simulation results show that the passive matching network can improve the real part characteristics of the antenna input impedance.Finally,the non-foster circuit and monopole antenna are processed,and the input impedance and the reflection coefficient of the monopole antenna matching the non-foster circuit are tested.The test results show that the negative capacitance produced by the non-foster matching circuit can effectively cancel the large reactance of monopole antenna,thus expanding the impedance bandwidth of the antenna and realizing wideband miniaturization.