<title>Photonically controlled phased arrays</title>

Abstract

We review our progress in the demonstration of photonically controlled phased arrays. In particular, we emphasize the impact made by photonic phased arrays steered via true-time-delay. We describe, in addition, a photonic beamforming architecture that combines RF-heterodyning with a Rotman lens feed for multiple beam formation.

Photonics for microwave systems and ultra-wideband signal processing

“…In summary, we have reviewed several demonstrations in a few topical areas that are The early work in MWP were aimed at demonstrating the modulation of high frequency RFsignals onto optical carriers, using photonic devices (directly modulated lasers or EOMs) that were still in their infancy. However, they provided opportunities [e.g., 17,[19][20] for workers in the optoelectronics field to interact with microwave/antenna engineers responsible for integrating the "photonic black boxes" into their host-systems. Based on these interactions, link models were developed to estimate the link G, NF and SFDR, parameters that became recognized as key metrics for system insertion [3,12].…”

“…In the 1990's, a series of pioneering work in the optical control of microwave phased array antennas [1][2][17][18][19][20] were accomplished to demonstrate true-time-delay (TTD) beamsteering, and the insertion of ruggedized RF-photonic links in antenna systems. It is well known that TTD steering can eliminate the phenomenon of beam squint [17] that occurs in phased arrays when "phase-shifters" -as opposed to "time-shifters" -are used to form beams at distinct RF frequencies.…”

“…Details of the optical beamforming network (BFN) design, construction and its operation are The above demonstration of a transmit phased array was followed by the construction of a 96-element L-band radar [19][20] that operated with ~50% instantaneous bandwidth (IBW) at Lband (0.85-1.4 GHz). The radar, comprised of eight subarrays, was designed to form beams that support a wide scan range of ±60 from a conformal aperture with a 10 ft radius of curvature (see Fig.2a).…”

“…The large aperture size and wide angular scan-range for this radar imposed a differential time-delay as long as ~7.75 nsec for its BFN, which was designed to deliver 10-11 bits of resolution. We again used [19][20] the switching of optical delay-lines -formed using fibers or silica waveguides -to generate programmable time-delays for the 4-5 major bits that steer the eight subarrays. Inside the subarrays, electronic time-shifters comprised of microstrip lines were incorporated to obtain 5-6 more bits of resolution.…”

Requirements for true time delay imaging systems with photonic components

“…For instance, in photonic true time delay (TTD) systems, it is common to use highly dispersive chirped Bragg gratings to create delay lines with time delays varying according to the optical carrier. However, these Bragg gratings can cause both amplitude fading if the dispersion is large enough [4]. More importantly, their group delay ripple in the optical region will affect the RF transfer function.…”