A non-Foster circuit (NFC) based on the resonant tunneling diode (RTD) is proposed for application to broadband impedance matching of electrically small antennas (ESAs). NFCs have traditionally been implemented with transistor pairs to achieve negative impedance, but these have limitations with respect to performance and operational bandwidth at high frequencies. At certain biasing voltages, double barrier RTDs behave as negative differential resistance (NDR) devices, which may be transformed to exhibit negative impedance. In contrast to the transistor-based NFC, these structures serve to gyrate or invert the load impedance, such that an inductive load will lead to a negative capacitance, and vice versa. This device is termed a negative impedance inverter (NII). We demonstrate negative impedance behavior for prototypes with measurements of negative resistance at up to 3 GHz, and device gain of around 5 dB from DC to 4 GHz. Design for stability of the RTD is performed using the Nyquist stability criterion. Stabilized negative capacitance NFCs show optimum performance from DC to the GHz range depending upon the load value. These NFCs are used to impedance match an antenna at low frequencies. An antenna with only one resonance at 3.5 GHz has been transformed with two different matching circuits: to an antenna encompassing the 1 to 2 GHz range; as well as the VHF/UHF bands from 300 MHz to 1 GHz. Additionally, RTDs have been demonstrated for operation at up to THz frequencies, so this topology can be extended to higher frequencies subject to fabrication constraints.
Index Termsresonant tunneling diodes (RTDs), non-Foster circuits (NFCs), stability, electrically small antenna (ESA).
The wave dispersion characteristics for loop array-based metamaterials were analyzed, based on the general transmission line model of a one-dimensional host medium interacting with a chain of coupled loops. By relating the wave propagation constant and the effective parameters of the coupled host medium, we showed that an active medium embedded with non-Foster loaded loop array can be designed to exhibit broadband negative material parameters with positive gain. Accounting for all interactions, the stability of the active medium was investigated, further yielding necessary design specifications for the non-Foster loads. Subsequently, an experimental demonstration was provided to verify the theoretical analysis, showing that stable reconfigurable broadband gain metamaterials at microwave frequencies can be obtained with proper negative impedance converter design.
This paper explores the fight against corruption through the eyes of Anna Hazare, a renowned social activist from India, who spent more than 35 years of his life fighting corruption. AnnaHazare provides a detailed description of the anti-corruption movement he has led, provides his views on the World Bank guidelines to lower corruption, and highlights the need for sacrifice and righteousness on the part of leaders who fight corruption. The paper presents insights into these concepts, which deserve greater attention from organization scholars and must be researched further if the literature on corruption is to be enriched.
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