Low-distortion long variable delay of linear frequency modulated waveforms

The impulse response of 500-MHz-wide, linear frequency modulated (LFM) waveforms is delayed and advanced by ±50 ns using microwave-photonic processing. The delays are obtained through the application of a variable frequency offset to a single optical sideband using an acousto-optic modulator. The peak-to-sidelobe ratio (PSLR) and integrated sidelobe ratio (ISLR) of the processed impulse response functions are higher than 18 and 20 dB, respectively, for the entire range of delay and advancement. The ISLR is 14 dB better than that of corresponding previous demonstrations. The results provide, for the first time, 100-ns microwave-photonic delay variations of practical radar signals with a high fidelity that complies with application standards. The method is applicable to LFM waveforms of arbitrary bandwidths and central radio frequencies.