A novel photonic-assisted deramp receiver extends detection distance along range direction of linearly-frequency-modulated continuous wave (LFM-CW) radars is proposed. A dual-polarization quadrature phase shift keying (DP-QPSK) modulator is used to modulate an optical frequency-comb (OFC) to generate orthogonally polarized optical signals. Then the orthogonally polarized optical signals are coherently detected with an optical local oscillator (OLO), which is generated by modulating the other OFC with the RF-reference signal on a null-biased Mach-Zehnder modulator (MZM). At the output of each detection unit, beating results can be recovered using a digital signal processing algorithm. By stitching the beating results of several paralleled detection units, the deramp signal corresponded to an extended range distance can be recovered. The proposed technique is experimentally evaluated through both simulated echoes and real echoes of two static trihedral corner reflectors (TCRs) distributed along range direction.