Linearly chirped signals with long temporal duration are generated by adding a dispersive loop in the photonic time-stretched coherent radar. The signal-to-noise ratio (SNR) variation of the optical pulse recirculation is analyzed and simulated to evaluate the multiple extension of temporal duration. The achievable temporal duration is confined by the dispersion and the amplified spontaneous emission noise accumulation. The experimental results verify the SNR variation of the optical pulse recirculation. Moreover, tunable linearly chirped signals with temporal duration of 100 ns and a bandwidth of 4 GHz at X or Ku band are generated. With the improvement of the time-bandwidth product, a drone can be successfully observed.