Ultra-wideband RF photonic phased array antenna

Date
2016
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University of Delaware
Abstract
Modern RF antenna systems are being asked to address many simultaneous and pressing challenges, e.g., wide operational bandwidth, dynamic gain profiles, and conformal profiles. One way to address these is to develop a flexible 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, presented is an optical feeding technique to achieve efficient excitation of an 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 population of more densely packed arrays, namely the CA, which offers potentially wide operational bandwidth. Additionally, 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 along with variable gain with suitable apodization. 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 feed point. Recently, however, modified uni-travelling carrier (MUTC) photodiodes, flip-chip bonded to high-thermal conductivity aluminum nitride (AlN), have achieved output powers of over 1 W at 10 GHz under CW operation [37], and over 10 W using pulsed power modulation [38]. A robust prototype MUTC photodiode-integrated antenna array on AlN with direct fiber feed to each antenna element is discussed and demonstrated that provides 5-20 GHz bandwidth and size, weight, and power (SWaP) superior to conventional electronic phased array systems [44].
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