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The newly discovered “long-term” multicarrier multipactors that can be induced by low-energy electric fields potentially threatens the reliability of spaceborne microwave systems. It also causes a new technical challenge to the prediction of the global occurrence threshold of multicarrier multipactors. In this paper, we propose efficient approaches to rapidly compute the fluctuation of space electrons in the evolving process of a multicarrier multipactor, based on which Monte Carlo approaches are developed to efficiently find the global “worst case” waveforms and the occurrence thresholds for both “single-event” and “long-term” multipactors. The proposed approaches can be used for wideband devices, providing an efficient integrated solution for the multicarrier multipactor analysis for practical high-power microwave devices with inhomogeneous field distribution. [ABSTRACT FROM PUBLISHER]

Coupled electromagnetic resonances have various important applications in microwave engineering. Among them, the newly discovered electromagnetically induced transparency (EIT) has attracted much interest. In this paper, we explore the use of configurable electrically induced transparency to construct a microwave “diffractive medium” whose air-like optimally matched transparency and metal-like optimally reflective opacity can be conveniently switched by a binary dc voltage. Different from EITs based on closely coupled resonances, we use decoupled electrically induced resonances to achieve a low-loss transparency along with an optimal impedance matching with air. Satisfying the condition of a lossless perfectly matched layer, such transparency and opacity can be obtained in a wide range of incident angles. We validate our approach by experimentally demonstrating two electrically controlled steering antennas based on diffractive grating effect, both with thin planar apertures and binary digital control circuits. The proposed approach can be extended to higher frequencies, achieving configurable diffractive devices at millimeter-wave and terahertz frequencies. [ABSTRACT FROM PUBLISHER]

Reports on the fabrication of a left-handed metamaterial with negative permittivity and permeability simultaneously in a specific small frequency band. Performance of refraction and beam-shifting experiments using triangular-shaped and parallelogram-shaped sample; Description of the refraction experiment.

In Physics, causality is a fundamental postulation arising from the second law of thermodynamics. It states that, the cause of an event precedes its effect. In the context of Electromagnetics, the relativistic causality limits the upper bound of the velocity of information, which is carried by electromagnetic wave packets, to the speed of light in free space (c). In anomalously dispersive media (ADM), it has been shown that, wave packets appear to propagate with a superluminal or even negative group velocity. However, Sommerfeld and Brillouin pointed out that the 'front' of such wave packets, known as the initial point of the Sommerfeld precursor, always travels at c. In this work, we investigate the negative-group-velocity transmission of half-sine wave packets. We experimentally observe the wave front and the distortion of modulated wave packets propagating with a negative group velocity in a passive artificial ADM in microwave regime. Different from previous literature on the propagation of superluminal Gaussian packets, strongly distorted sinusoidal packets with non-superluminal wave fronts were observed. This result agrees with Brillouin's assertion, i.e., the severe distortion of seemingly superluminal wave packets makes the definition of group velocity physically meaningless in the anomalously dispersive region. [ABSTRACT FROM AUTHOR]

Abstract: We present the first study of the hybridizing effect of different left-handed metamaterials (LHM) based on S-shaped and Ω-shaped resonators. Three different cases of hybridizing are investigated, ten configurations of various hybrid ratio are simulated, fabricated and measured, and a series of different left-handed passbands is obtained, showing that the left-handed passband of the proposed hybrid structure can be controlled by tuning the hybrid ratio. The hybrid left-handed metamaterial proposed in this Letter has potential applications in LHM-based filters, couplers, antennas, etc. [Copyright &y& Elsevier]