Study Of Active Broadband Miniaturized Antenna For Mobile Terminal

Terminal antenna is in a key position in wireless communication equipment.The performance of terminal antenna directly affects the communication quality of wireless communication equipment.Now the terminal equipment in wireless communication is developing towards the trend of simple appearance and beautiful technology and superior performance,which requires that the terminal antenna must be miniaturized and wideband.Passive wideband miniaturization technology is limited by the gain-bandwidth-volume theory.In this paper,the application of non-foster active circuit to wideband miniaturization of terminal antenna can effectively realize the wideband of small-size terminal antenna.By combining the negative capacitance generated by non-foster circuit with the small-size terminal antenna,a miniaturized and wideband terminal antenna is designed,which is of great research value for the development of multi-antenna and multi-band mobile phones in the future.Based on the analysis and simulation design of the principle,and the actual processing test,this paper studies the broadband matching of terminal antenna based on the non-foster reactance circuit.The main tasks completed are:1.Summarized the basic principles and implementation methods of the non-foster circuit,and designed the non-foster circuit covering the GSM/LTE low-end frequency band(500MHz-1500MHz)of the mobile phone antenna according to the non-foster reactance theory.The simulation software Keysight ADS was used to carry out the simulation design of the non-foster circuit,and negative impedance converters(NICs)that is based on the transistor s-parameter model and that is based on actual packaged model were respectively established.The simulation results showed that negative capacitance could be generated at the input-end of the NIC.The influence of parameter variation on input impedance characteristics is analyzed,and the stability of the circuit is also analyzed.The software simulation verifies that the negative capacitance generated by the non-foster circuit can offset the positive capacitance in the antenna equivalent circuit so as to realize the broadband matching.2.Having designed a small-size inverted L-type planar monopole terminal antenna,its operating band is among 500 MHZ to 1500 MHZ,the horizontal length and vertical length of inverted L-type patch is 10 mm,the antenna impedance characteristics has been simulated by electromagnetic simulation software ANSYS HFSS,taking extraction of the antenna S parameters and input impedance parameters,then respectively designed LC passive matching network based on discrete device and active matching networks based on the circuit foster,comparing the differences of two matching method,the active matching in the broadband antenna miniaturization has prominent advantages.Finally,the actual non-foster circuit and inverted-L mobile phone antenna are processed,the impedance characteristics of the non-foster circuit are tested,and the S11 of the mobile phone antenna with active matching is tested.The results show that the negative capacitance generated by the nonfoster circuit can offset the strong capacitive reactance of the antenna,and finally the broadband miniaturization of the mobile phone antenna can be realized.