Limitation of Negative Impedance Converter using Operational Amplifier for matching electrically small antenna

This paper investigates the limitation of Negative Impedance Converter (NIC) using Operational Amplifier (Op-Amp). The limitation is theoretical analyzed and then experimentally verified. The results show that, the Op-Amp based NIC has complex input impedance. In addition, the input impedance presents a negative resistance with large magnitude, if a negative small capacitance is desired for matching an electrically small antenna. Therefore, an Op-Amp based NIC reduces the efficiency of the whole matching network, and limits its application in matching electrically small dipole or monopole antenna with large negative capacitive reactance.