A Systemized View of Superluminal Wave Propagation

Withayachumnankul, Withawat; Fischer, Bernd; Ferguson, Bradley S.; Davis, B.R.; Abbott, Derek

doi:10.1109/jproc.2010.2052910

Cited by 42 publications

(19 citation statements)

References 51 publications

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“…However, in a highly dispersive system, the group delay can be negative at a certain frequency range. Some describe this phenomenon as "superluminal propagation", implying the group velocity in the system is greater than the speed of light [16][17][18]. Contrarily, the opposing part claims that NGD is no other than the result of excessive phase shift or waveform dispersion [19,20].…”

Section: Ngd For Mimo Antennasmentioning

confidence: 99%

Low Correlation Mimo Antennas With Negative Group Delay

Chung¹,

Yang²,

Lee³

2011

PIER C

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A key feature of upcoming 4G wireless communication systems is multiple-input-multiple-output (MIMO) technology. To make the best use of MIMO, the antenna correlation between adjacent antennas should be low (< 0.5). In this context, we propose a correlation reduction technique suitable for closely spaced antennas (distance, d < λ/40). This technique reduces mutual coupling between antennas and concurrently uncorrelates antennas' radiation characteristics by inducing the negative group delay at the target frequency. The validity of the technique is demonstrated with a USB dongle MIMO antenna designed for LTE 700 MHz band. Measurement results show that the antenna correlation is reduced more than 40% using the proposed technique.

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Section: Ngd For Mimo Antennasmentioning

confidence: 99%

Low Correlation Mimo Antennas With Negative Group Delay

Chung¹,

Yang²,

Lee³

2011

PIER C

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“…Note that the dispersion curve in Fig. 3(a) exhibits a round shape including also a point with infinite group velocity [3,23], where dβ/dk = 0. This point is outside the operation window for our protocol.…”

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confidence: 99%

Light Stops at Exceptional Points

2018

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Almost twenty years ago, light was slowed down to less than 10^{-7} of its vacuum speed in a cloud of ultracold atoms of sodium. Upon a sudden turn-off of the coupling laser, a slow light pulse can be imprinted on cold atoms such that it can be read out and converted into a photon again. In this process, the light is stopped by absorbing it and storing its shape within the atomic ensemble. Alternatively, the light can be stopped at the band edge in photonic-crystal waveguides, where the group speed vanishes. Here, we extend the phenomenon of stopped light to the new field of parity-time (PT) symmetric systems. We show that zero group speed in PT symmetric optical waveguides can be achieved if the system is prepared at an exceptional point, where two optical modes coalesce. This effect can be tuned for optical pulses in a wide range of frequencies and bandwidths, as we demonstrate in a system of coupled waveguides with gain and loss.

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“…Therefore, the velocity of the start and end of the information cannot exceed . To put it another way, as discussed in [11], [12], and [28], the speed of the information is determined by the "precursor velocity" or the "front velocity" rather than the group velocity, and they are never faster than . However, the "precursor velocity" or the "front velocity" argument can not clearly and comprehensively answer the question of whether a band-limited "superluminal" propagation exists or not, and thus it is still an open question calling for further scientific debate.…”

Section: Discussion On Relativity Stability and Causalitymentioning

confidence: 99%

“…Regarding the stability and causality, if the system is stable and causal, the magnitude and the phase of the system response must follow Kramers-Kronig relations [28], [29] as (15) where and are the phase and magnitude of a system response, respectively. In order to verify the causality and stability of this system, the magnitude of the measured from dc to 10 GHz were applied to (15), the calculated phase (dashed red curve in online version) is compared with the measured phase of (solid blue curve in online version) in Fig.…”

Section: Discussion On Relativity Stability and Causalitymentioning

confidence: 99%

Broadband Fast-Wave Propagation in a Non-Foster Circuit Loaded Waveguide

Long

Jacob

Sievenpiper

2014

IEEE Trans. Microwave Theory Techn.

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Abstract-Frequency independent fast-wave (FW) propagation with phase velocity greater than the speed of light can be ideally realized in a dielectric medium whose relative permittivity is positive, but less than 1. Conventionally, FW propagation is implemented by non-TEM waveguides or antiresonance-based metamaterials, which suffers from the narrow bandwidth due to the dispersion. In contrast, non-Foster circuits provide a brand new method for reducing the dispersion so as to broaden the bandwidth. This paper demonstrates broadband FW propagation in a microstrip line that is periodically loaded with non-Foster circuits. Discrete transistorbased non-Foster circuits functioning as negative capacitors are successfully designed with the novel modified negative impedance converter circuits. A 10-pF negative capacitor over a bandwidth of 10-150 MHz has been implemented. The fabricated circuits have been integrated into a microstrip line to form a FW waveguide. The retrieved phase velocity of the effective medium from the measured -parameters characterizes a stable and causal FW medium with constant phase velocity of from 60 to 120 MHz, and this has been further verified by Kramers-Kronig relations and the near-field measurements along the waveguide. In conclusion, a stable, causal, and broadband FW waveguide has been achieved by means of transistor-based non-Foster circuits. The implemented broadband FW propagation can potentially be applied in broadband leaky-wave antennas and cloaking techniques.Index Terms-Fast-wave (FW), metamaterials, non-Foster circuits, periodically loaded transmission line.

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A Systemized View of Superluminal Wave Propagation

Cited by 42 publications

References 51 publications

Low Correlation Mimo Antennas With Negative Group Delay

Low Correlation Mimo Antennas With Negative Group Delay

Light Stops at Exceptional Points

Broadband Fast-Wave Propagation in a Non-Foster Circuit Loaded Waveguide

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