Reflected power measurement of antennas by using an alternative microwave photonic system is presented in this paper. The proposed experimental setup is based on optical mixing of two distributed feedback (DFB) lasers, where combined beams are detected by a photodetector. The resulting photocurrent corresponds to a microwave signal which is continuously tuned on band-widths from 0 to 4 GHz. The obtained swept frequency is applied to an antenna in order to measure its reflected power. Error sources that limit the measurement accuracy of optical mixing such as effect of power deviation in the linewidth of the beat signal and errors introduced by extra fixture are studied. Results of the measurements obtained with the proposed photonic technique are calibrated and compared with traditional electrical measurements. The most important motivation on the use of the proposed technique in this paper lies in that with a simple configuration we were able to characterize microwave devices in a very wide frequency range, avoiding the use of a vector network analyzer (VNA), and thus, a complicated and tedious calibration procedure, contributing to the field of instrumentation and characterization by using photonic techniques.