Microwave Correlator Based on a Nonuniformly Spaced Photonic Microwave Delay-Line Filter

We propose and demonstrate a novel technique to perform matched filtering of a phase-coded microwave signal using a photonic microwave delay-line filter. The photonic microwave delay-line filter is designed to have a frequency response that is conjugate to the spectrum of the phase-coded microwave signal. To implement the delay-line filter, the tap coefficients are usually complex, which is difficult to implement in the optical domain. In this letter, a photonic microwave delay-line filter with equivalent complex coefficients implemented using an all-positive-coefficient photonic microwave delay-line filter based on a nonuniformly spaced delay-line structure is proposed. Since only positive coefficients are required, the implementation of the filter is greatly simplified. An experiment is performed. The decoding of a 6.75-GHz binary-phase-coded microwave signal is experimentally demonstrated.