USA As Represented by Secretary of the Navy

Government of the United States of America, As Represented by the Secretary of Commerce

Other

The United States of America

Eung Gi Paek

Joon Y Choe

Mark G Parent

Charles L Wilson

Craig I Watson

The basic concept of satellite-free time transfer using time reversal (T3R) has been invented and successfully demonstrated over long distance (about 4,000 km) with an accuracy of approximately 200 ns rms. The current invention describes new methods to drastically improve performance up to &#x3c;10 ns rms&#x2014;better than the current differential GPS, without satellites. The new method employs the Vernier concept utilizing the unique p-independence property of T3R irrespective of carrier frequencies. Also, a histogram method to automatically filter out extraneous data and allow high accuracy and a new method to extend the timing range of T3R beyond the pulse repetition period by removing ambiguity are proposed. A systematic way to obviate the signal blockage caused by transmit/receive window mismatch, is also proposed. Issues and solutions associated with the ionosphere are proposed, including 24-7 operation in adverse ionospheric conditions, such as the constantly changing ionosphere, multiple hops, static asymmetry, and jamming and spoofing.

High-performance time transfer using time reversal (T3R)

A distributed time reversal mirror array (DTRMA) system includes a plurality of independent, sparsely distributed time reversal mirrors (TRMs). Each of the TRMs includes an antenna; a transceiver connected to the antenna for transmitting a signal toward a target, for receiving a return, reflected signal from the target, and for retransmitting a time-reversed signal toward the target: means for phase-locking and for maintaining spatial and temporal coherences between the TRMs; and a computer including a machine-readable storage media having programmed instructions stored thereon for computing and generating the time-reversed retransmitted signal, thereby providing a phased array functionality for the DTRMA while minimizing distortion from external sources. The DTRMA is capable of operating in an autonomous, unattended, and passive state, owing to the time-reversal's self-focusing feature. The beam may be sharply focused on the target due to the coherently synthesized extended aperture over the entire array.

Distributed time-reversal mirror array

A Time Transfer Time Reverse Mirror (TT TRM) method and system includes a radio transceiver for transmitting a series of short pulses repeatedly at a period T and for receiving from a remote node a return signal that is a retransmission of the original signal at the same period T: a clock circuit for inputting a clock signal to the transceiver: and a computer for (i) computing and generating an imaginary time-reversed signal version of the original signal, (ii) comparing the return signal with the imaginary version, (iii) computing a delay between the return signal and the imaginary version that is substantially equal to twice the time difference between the two nodes, and (iv) applying the computed delay to a clock input calibration for a desired signal. The system includes time transfer using the ionospheric reflection (refraction), producing precise synchronization among remote nodes beyond the line-of-sight and thus without necessitating GPS or communication satellites.

Time transfer method and system

A phased array antenna system includes an RF front end, a radome, and an optical calibrator embedded in the radome for enabling in-situ calibration of the RF front end. The optical calibrator employs an optical timing signal generator (OTSG), a Variable Optical Amplitude and Delay Generator array (VOADGA) for receiving the modulated optical output signal and generating a plurality of VOADGA timing signals, and an optical timing signal distributor (OTSD). The in-situ optical calibrator allows for reduced calibration time and makes it feasible to perform calibration whenever necessary.

Antenna calibration method and system

A time-reversal imaging radar system for acquiring an image of a remote target includes an antenna array having a plurality of spaced-apart antennas, and a transceiver coupled to the antenna array for alternately transmitting a radar signal via the antenna array toward the target and for receiving target-reflected radar signals. The transceiver includes means for multiple-pass time-reversing the transmitted and received radar signals whereby coherent beam focusing is realized at both the target and at the receiver to thereby enhance the resolution of the acquired target image.

Imaging radar method and system

System and method for rapidly reconfigurable two-dimensional true time delay generation for phased array antennas is described. The system utilizes a broadband light source, an array of fiber chirp gratings in a single fiber, and an acousto-optic spectrometer to generate a time-delayed linear grating. The grating is subsequently rotated to the desired angle utilizing an acousto-optic device having no moving parts.

True time delay generating system and method

True time delay generation utilizing broadband light source with fiber chirp grating array and acousto-optic beam steering and 2-D architectures

A method for improving the quality of holographic images by reducing local noise in a holographic memory system is disclosed. The method is characterized by: storing a white reference image and a black reference image in the memory system, storing a series of data images in the memory system, applying a simple model based on a point-to-point of linear interpolation to the series of data images, the white reference image and the black reference image to provide a series of corrected data images having reduced noise. The simple model is preferably in the form of

Noise reduction in volume holographic memories

An acousto-optic tunable filter and filtering method are disclosed providing for a significantly increased number of available wavelength channels for output. The filter combines a diffraction grating, the grating vector of which is transverse to light propagation direction, with an acousto-optic beam deflector, which, by accommodating a narrow spectral bandwidth (about 5% that of conventional acousto-optic tunable filters), provides significantly increased output bandwidth and available wavelength channels (by a factor of approximately 20).

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Germantown, MD, United States of America

Eung Gi Paek