Research On Broadband Small Antennas Loaded Non-foster Matching Network

In the recent years, the devices of communication systems are more and moreminiaturized and wideband. As an important part of communication systems,broadband small antennas are researched increasingly. For electrically smallantennas, the effectiveness of passive matching is severely limited byGain-bandwidth theory. The non-foster impedance matching network can breakthrough the theory, and improve the performance of the antennas. So the research ofthe non-foster matching network is booming.In this paper, the history and the background of non-foster impedancematching network is presented firstly. Then the theory of negative impedanceconverter (NIC) is researched, especially the NIC built by Linvill. We built theschematic of non-foster impedance matching network in ADS. The stability hasbeen tested by Nyquist stability criterion, Harmonic balance simulation andTransient simulation. The inductances have been used to make the circuit stable.The circuit confirms that the circuit can convert the passive impedance to negativeimpedance.An electrically small antenna was designed and tested by the vector networkanalyzer. The equivalent circuit was built by the data. An investigation of theantenna loaded with non-foster impedance matching network was performed. In thesame way, the stability of the circuit is studied. The inductances and resistors areused to make sure that the circuit is stable. Furthermore, a passive impedancematching network is designed and loaded to the a ntenna loaded with non-fosterimpedance matching network, so that antenna achieves the miniaturized andbroadband characteristic. Finally, the gain improvement by the matching network iscalculated.