Paul J. Matthews

Fiber-optic true time steering of an ultrawide-band receive array

We report the development and demonstration of the first true time-delay (TTD) fiber-optic beamformer for ultrawideband antenna receive operation. The beamformer is based on a dispersive-fiber prism configuration that properly time delays the signals originating at each receiving element for coherent combining in the microwave domain. The time-steered receive antenna consists of eight spiral elements arranged into a one-dimensional (l-D) sparsely populated array. The receive array shows an instantaneous bandwidth of 6-18 GHz, limited by the available matched microwave amplifiers. The array performance is measured in an anechoic chamber and exhibits unprecedented squint-free steering over an azimuth scan of 120/spl deg/ over the full frequency range.

A wide-band fiber-optic true-time-steered array receiver capable of multiple independent simultaneous beams

A wide-band fiber-optic true-time-delay array receiver capable of receiving multiple independent beams simultaneously is demonstrated for the first time. The receiver is based on a dispersive prism technique and exhibits squint-free /spl plusmn/60/spl deg/ azimuthal steering of two simultaneous beams with no observable beam squint over a microwave component-limited bandwidth of 6-18 GHz.

Practical photonic beamforming

The impetus for future array antenna systems has revolved around the demands for increased capabilities in array antennas including larger arrays higher power and better angular resolution, wide bandwidths, reconfigurability and higher operating frequencies. In order to move microwave photonics technology for array antennas beyond the proof-of-concept phase and to compete with alternate approaches, the community must be quicker to grasp the systems issues involved. This paper surveys some of the photonics techniques for optical control of array antennas, addresses the system-level issues for technology insertion and discusses some of the competing technologies.

Photonic analog-to-digital conversion by distributed phase modulation

A photonic analog-to-digital converter with a binary optical output was constructed. The architecture scheme is a pipeline analog-to-digital converter, employing phase modulators and polarization-based optics. The result is a photonic analog signal processor that maps an input analog waveform into a binary output. The operational speed of the conversion is primarily limited by the maximum slew rate of the phase modulators.

Ultrawide-band fiber-optic control of a millimeter-wave transmit beamformer

An ultrawide-band fiber-optic true time-delay millimeter-wave array transmitter is fully characterized and demonstrated in this paper. The beamformer is based on dispersive-prism optical-delay lines and exhibits squint-free /spl plusmn/60/spl deg/ steering in azimuth across the entire Ka-band (26.5-40 GHz). This is believed to be the first fully functioning demonstration of a photonically controlled wide-band millimeter-wave transmitter system.

Sub-10 femtosecond timing jitter of a 10-GHz harmonically mode-locked fiber laser

We present the lowest measurements of timing jitter, to our knowledge, of a harmonically mode-locked fiber laser. Phase detection noise measurements demonstrate a timing jitter of less than 10 fs from 100 Hz to 1 MHz.

Demonstration of a wide-band fiber-optic nulling system for array antennas

A novel technique for forming and steering squint-free wide-band nulls in the far-field pattern of an ultrawide-band array antenna is presented. The nulling system relies upon a fiber-optic dispersive prism tapped delay-line microwave filter to generate the appropriate nulling waveform. The null-forming architecture was integrated with a wide-band fiber-optic dispersive prism true-time-delay transmit beamformer for demonstration in an anechoic chamber. Measurements show null depths of the order of 15 dB over the 4-18-GHz bandwidth of the system for various steering angles. The demonstrated architecture may be used for simultaneous wide-band beamforming, sidelobe reduction, and jammer suppression.

RF phase-noise performance of a two-channel optical downconverting link for microwave phase detection

The phase-noise performance of a low-noise preamplified two-channel optical downconverting link is measured for the first time. The downconverter is capable of operation over a 2-18-GHz bandwidth with a fixed intermediate frequency of 160 MHz. Results show that a two-channel configuration used as a remote microwave phase detector exhibits performance equivalent to a typical microwave mixer.

Real-time photonic analog-digital converter based on discrete wavelength-time mapping

A real-time two-channel photonic analog-digital converter operating at >2 GSPS has been constructed and demonstrated for the first time, to our knowledge. The architecture is based on the time-interleaving of discrete, spectrally-distinct optical pulses.

Photonic signal processing for microwave applications

The use of photonic techniques for microwave signal processing has the potential to bring improved performance and new capabilities to RF and microwave systems. Due to this promise, a large number of organizations are vigorously pursuing the processing of signals using photonics. Several recent demonstrations have illustrated the increasing maturity of the field. Here, we briefly present the motivations behind this growing effort and review the current capabilities of photonics.