A harmonics-based retrodirective system (HBRS) is proposed for microwave power transfer to an airplane for weight saving. Re-radiation of rectenna harmonics is adopted for the pilot signal in the HBRS. It is necessary for actualizing the HBRS to evaluate harmonic re-radiation from rectennas. In this paper, we fabricated rectennas which are on a thin and lightweight substrate, and conducted experiments. From measurements with a single rectenna, we obtained re-radiation patterns which agreed with the electromagnetic simulation. The re-radiation patterns from the array of two rectenna were consisted with the patterns which were calculated from the array factor.