Optically addressed ultra-wideband connected array antenna

Abstract

Modern RF antenna systems are being asked to address many simultaneous and pressing challenges, e.g., wide operational bandwidth, dynamic gain patterns, and conformal profiles. One way to address these problems is to develop a low profile and ultra-wideband (UWB) phased array antenna. However, the design, fabrication, and integration of such an array using an all-RF feed is exceedingly difficult. Thus, in this paper we present a novel optical feeding technique to achieve efficient excitation of a UWB connected array (CA) antenna. By feeding the array optically, preservation of the theoretical bandwidth and low-profile of elementary connected dipole elements is enabled. Coupling of light to a photodiode merely requires enough space to firmly secure a fiber ferrule, allowing for the population of more densely packed arrays and wider operational bandwidth. Additionally, the optical feeding of the array can provide low noise excitation of the radiating elements, which supports high fidelity beam steering of independent signals over the array's ultra-wide bandwidth. Currently all of these abilities are unattainable by conventional electronic feeding networks. Previously the main limiting factor for the realization of such an optical system was the low power handling capability of the photodiode at the antenna excitation point. Recently, however, modified uni-travelling carrier (MUTC) photodiodes, flip-chip bonded to high-thermal conductivity aluminum nitride (AlN), have been able to achieve output powers of over 1 W at 10 GHz under CW operation, and over 10 W using pulsed power modulation. A prototype MUTC photodiode-integrated antenna array on AlN with direct fiber feed to each antenna element is discussed and demonstrated that can provide 5–20 GHz bandwidth and a size, weight, and power (SWaP) superior to conventional electronic phased array systems.