Analysis of Photonics-Based RF Beamforming With Large Instantaneous Bandwidth

Since the photonics-based true time delay could significantly broaden the instantaneous bandwidth of a phased antenna array system, solutions utilizing wideband signals could be enabled to considerably enhance the functionality and performance of RF systems. To investigate the features of the wideband beamforming, a comprehensive theoretical model is developed in this paper to analyze the photonics-based broadband beamforming network for uniform linear arrays. In the proposed model, the performance of the beamforming network over the operational frequency band is intuitively depicted through a two-dimensional spatial-temporal frequency response, in which both the spatial frequency (or the corresponding observation angle) and the temporal frequency are adopted as independent variables. In addition, cross correlation of the original signal and the signal that undergoes the beamforming network is calculated to define a wideband pattern and a new figure of merit, so that the waveform-dependent overall response over a large bandwidth can be evaluated. Based on the theoretical model, a time-domain method for pattern measurement is proposed and experimentally demonstrated, which offers the coincident result as the frequency-domain method but is more convenient to be conducted. Numerical results of several typical photonics-based beamforming structures are presented to investigate the impact of nonidealities on the two-dimensional response and the proposed figure of merit.