Deepak Singh Nagarkoti

An Active Wideband and Wide-Angle Electromagnetic Absorber at Microwave Frequencies

Two-dimensional (2-D) metamaterials (MTMs) can be used to create perfect electromagnetic absorbers. In this letter, a novel active MTM absorber with non-Foster loads is proposed. For obliquely incident plane waves with both transverse-electric (TE) and transverse-magnetic (TM) polarizations, its effective circuit model is analytically demonstrated, accounting the material losses. Based on the circuit model, a stability characterization is introduced to give the design principles for the non-Foster elements to achieve a wideband and wide-angle metamaterial absorber (MA). These active elements are achieved by a two-port non-Foster circuit based on the resonant tunneling diodes. For the purpose of verification, a sample active MA design is presented, exhibiting a high electromagnetic absorption rate for wideband and wide-angle incidence for both TE and TM polarizations at microwave frequencies, as compared to its passive counterpart.

Graphene-based tunable non-foster circuit for VHF applications

This paper presents a negative impedance converter (NIC) based on graphene field effect transistors (GFETs) for VHF applications. The NIC is designed following Linvill’s open circuit stable (OCS) topology. The DC modelling parameters of GFET are extracted from a device measured by Meric et al. [IEEE Electron Devices Meeting, 23.2.1 (2010)] Estimated parasitics are also taken into account. Simulation results from Keysight Advanced Design System (ADS) show good NIC performance up to 200 MHz and the value of negative capacitance is directly proportional to the capacitive load. In addition, it has been shown that by varying the supply voltage the value of negative capacitance can also be tuned. The NIC stability has been tested up to 2 GHz (10 times the maximum operation frequency) using Nyquist stability criterion to ensure there are no oscillation issues.

Wave propagation in reconfigurable broadband gain metamaterials at microwave frequencies

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.

Anna Hazare A Corruption Crusader and His Grassroots Wisdom

This article 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. Anna Hazare 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 article 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.

Beam-Steering Performance of Flat Luneburg Lens at 60 GHz for Future Wireless Communications

The beam-steering capabilities of a simplified flat Luneburg lens are reported at 60 GHz. The design of the lens is first described, using transformation electromagnetics, before discussion of the fabrication of the lens using casting of ceramic composites. The simulated beam-steering performance is shown, demonstrating that the lens, with only six layers and a highest permittivity of 12, achieves scan angles of 30° with gains of at least 18 dBi over a bandwidth from 57 to 66 GHz. To verify the simulations and further demonstrate the broadband nature of the lens, raw high definition video was transmitted over a wireless link at scan angles up to 36°.

Radiation-Q bound of a small non-Foster antenna

Within this article the fundamental limit of Q of an antenna with non-Foster elements will be proposed. The Chus fundamental radiation Q-limit of small antennas has been revisited for non-Foster small antennas, where non-Foster elements are assumed to be within the radiansphere. In the case, where non-Foster circuits are not part of the antenna itself, the fundamental limit for matching a high-Q antenna defined by Bode-Fano has been revisited using non-Foster matching technique. Furthermore, this paper will discuss how non-Foster antennas (NFAs) can overcome the fundamental Chus limit of small antennas depending upon the consideration of non-Foster elements as a part of antenna itself. Also, simulation results of Q-bound curve for a test antenna has been verified with measured non-Foster element.

Signal to noise ratio improvement with non-Foster antenna matching

This paper discusses the signal to noise ratio (SNR) improvement at the antenna receiver system output using non-Foster matching. High mismatch loss in an antenna reduces the external noise power below the internal noise floor which results in a lower SNR than expected appearing at the input of the receiver. Non-Foster matching can minimize the mismatch loss but also adds its own noise to the receiver circuit. Thus, the improvement of SNR is dependant upon the noise and loss added by the matching circuit.

Stability analysis of resonant tunnelling diode for resistive matching of an electrically small antenna

We present a method for broadband impedance matching of electrically small antennas (ESAs) using devices with negative differential resistance regions, and specifically a resonant tunelling diode (RTD). A scheme is presented for cancellation of the high reactance of the ESA, as well as overcoming the low radiation resistance. The scheme is designed for stable operation.