Correlation of radio-frequency (RF) signals is a fundamental operation in many fields such as information processing, detection, and imaging techniques at large. Because of the intrinsic limitations of electronic techniques, standard digital correlators, which rely on the acquisition of signals and their processing, become very complex to implement for the real-time analysis of signals whose bandwidth exceeds a few hundred MHz. On the other hand, analog correlators are limited by the performances of RF components. In this paper, we report the proof-of-concept of a correlator architecture based on a simple photonic platform, suitable for analog wideband RF signal processing. The concept, based on multi-heterodyne interferometry, gives access in real time to the entire correlation function of two signals by computing the cross correlation coefficients for 200 values of their relative delay simultaneously. The time-delay step can be adjusted from a few ns down to a few ps, enabling us to process signals with MHz to multi-GHz bandwidth. We have applied this architecture to the localization of RF transmitters by time difference of arrival (TDoA) and obtained a precision close to 10 ps for a 100 ms integration time. This concept is expected to find practical applications in various domains, from radar and electronic warfare to telecommunications, imaging, and radio-astronomy.