Experimental Demonstration of Op-Amp-Based Negative Inductor in Microwave Regime

This letter presents the methodology behind the design and development of a device that disobeys Foster’s reactance theorem and operates as a negative inductor in the microwave range. An operational amplifier (op-amp)-based negative impedance converter (NIC) is used to design a negative inductor (nonfoster element). The design concept is quantitatively analyzed, simulated, and experimentally verified. A co-simulation technique and some basic principles are presented to make it easier to build and optimize the negative inductor circuit. The simulation results show that the input admittance is negative from 1 to 4 GHz. The method of fabrication used is a hybrid microwave integrated circuit (HMIC). The methodology is verified by the measurement of a prototype whose size is $20\times 20$ mm ( $0.006\lambda _{0} \times 0.066\lambda _{0}$ ) with a thickness of h = 1.6 mm ( $0.0053\lambda _{0}$ ), where $\lambda _{0}$ is the free-space wavelength at 1 GHz. Good agreement between experimental data and theoretical predictions is observed for 1–4 GHz, proving the validity of the provided method. The proposed prototype can eliminate reactance in impedance matching while designing broadband RF antennas and absorbers. This is the first work which demonstrates the realization of negative inductor in using HMIC technology.