Conformal, low profile, and wideband phased arrays have received increasing attention due to their potential to provide multiple functionalities over several octaves of frequency, using shared common apertures for various applications, such as radar, ultra-fast data-links, communications, RF sensing, and imaging. These arrays offer tremendous advantages, including multiple independently steerable beams, polarization flexibility, and high reliability.
With high frequency operation, high input resistance in transmitting the RF signal driving to the antenna may cause an imbalanced operation of the radiating elements of the antenna. Conventional 50-Ω coaxial line feeding the RF signal to the antenna are often unsuited for a balanced operation of the antenna. As a result, a balanced-to-unbalanced transformer, i.e., a balun, as well as an impedance transformer, is typically provided for each radiating element. The use of these transformers, however, can impose additional restrictions on the performance of the antenna array, such as the bandwidth, operational frequency, weight and profile, particularly at high operational frequencies, conformability, overall compactness and the additional relative high costs of these components.
Use of certain structure associated with conventional antenna arrays (such as baluns, amplifiers and/or RF transmission lines) may be reduced or avoided altogether by optically feeding the RF information to the antenna array, such as with optical fibers. For example, in an optically-fed phased-array architecture, transmitting signals are converted from the electrical domain to the optical domain by using electro-optic (EO) modulators, transmitted to the antenna array via optical fibers. Each optical fiber outputs its optical signal to a photodiode/antenna pair, where the photodiode receives the optical signal output from the optical fiber and outputs an electrical signal to drive the antenna to which it is connected. Such antenna arrays can have low impact in the physical space they occupy, and may be implemented with a low height profile and may be formed conformally to non-planar surfaces. However, complexities in installation of the antenna array may make it difficult to easily take advantage of the small form factor and conformal configurations available for such optically fed antenna arrays.