Application Of Non-Foster Elements In Broadband Matching Networks And Absorbing Structures

With the rapid development of communication technology, miniaturization of wireless communication device is needed. As a key component in the wireless communication system, the performance of the antenna plays important roles. The research of the miniaturized and broadband antennas has become the new focus in the field of antenna research.Electrically-small antennas, usually working at VHF or lower frequency, are required in the applications of vehicular communication system, personal wireless communication equipment, etc. Unfortunately, the restrictive relation between the high quality factor and the bandwidth efficiency limits the application of the passive matching because of the realizability constraints imposed by the gain-bandwidth theory of Bode, Fano, and Youla. The limitation can be overcome by adopting the Non-Foster elements, which have the opposite properties of frequency response compared with the typical Foster elements. Hence, the research on wideband and stable Non-Foster elements attracts more interests in the design of the matching network. Furthermore, broadband matching is also the prerequisite to realize the broadband absorbing structure, employing Non-Foster elements is a new method in the design of broadband, ultrathin absorbers.This thesis first studies two types of Non-Foster circuits, namely operational amplifier NIC (negative impedance converter) and transistorized NIC. A novel and compact current feedback amplifier-based NIC (CFA-based NIC) has been proposed and realized. The measurement results show the negative inductivity of the input impedance over a wideband from 50 to 500 MHz. Especially, the equivalent inductor of the present circuit is -3.4 nH±10% from 200 to 500 MHz.Secondly, based on the study above, Non-Foster elements are embedded in a resonant printed electrically-small antenna to achieve broadband matching without increasing the size of the whole structure. The measured results show that for Non-Foster matching, the relative bandwidth of the antenna is 55.6%, while for passive matching, the relative bandwidth is 6.9%.Finally, this thesis investigates the application of Non-Foster elements in design of absorbing structure. The introduce principle of the Non-Foster elements is discussed. Then, the effective use of Non-Foster elements in absorbing structure is analyzed and the simulation and its equivalent circuit model is presented.