Radio signal transmission over optical fiber is considered a promising technology for future wireless communication applications, thanks to the advantages such as broad bandwidth, low loss, and the immunity to the electromagnetic interference. There are two schemes that are employed to transmit radio signals over optical fiber, the intensity modulation/direct detection (IM/DD) and remote heterodyne detection (RHD). For IM/DD scheme, the RF signal is intensity modulated onto the optical carrier at the transmitter and recovered by a photodiode at the remote end. The problem related to IM/DD scheme is that the chromatic dispersion caused by optical fiber leads to significant power penalty. To avoid chromatic dispersion-induced power penalty, RHD scheme is usually used. For RHD scheme, the RF signal is carried by two phase-locked optical carriers and is recovered at the remote end by a photodetector.
On the other hand, there have been great interests in the development of true time delay (TTD) beamforming techniques for phased array antennas. Phased array antennas using TTD techniques can provide wide instantaneous bandwidth without beam squint problem, which ensures an accurate delivery of radio signals. Different TTD beamforming techniques have been proposed, but all of them are based on IM/DD scheme, which has the problem of power penalty. In this paper, we propose to use RHD scheme for TTD beamforming, to avoid dispersion-induced power penalty. A fiber Bragg grating prism for broadband beamforming using discrete fiber Bragg gratings will be designed and implemented. Theoretical and experimental results will be reported.