Chirped Microwave Pulse Generation Using a Photonic Microwave Delay-Line Filter With a Quadratic Phase Response

We propose an optical approach to generating chirped microwave pulses using a photonic microwave delay-line filter (PMDLF) with a quadratic phase response. If a chirp-free broadband microwave pulse is inputted into the filter, a chirped microwave pulse is generated thanks to the quadratic phase response of the filter. To design a PMDLF with a quadratic phase response, complex tap coefficients are required, which is hard to implement in the optical domain. In this letter, a PMDLF with equivalent complex coefficients implemented based on a nonuniformly spaced delay-line structure is demonstrated. Since only positive coefficients are required, the filter is easy to implement. A design example is provided. A five-tap PMDLF to generate a chirped microwave pulse with a chirp rate of 13.2 GHz/ns is then experimentally demonstrated.