In this paper, a method is proposed to reduce the in-band radar cross section (RCS) of the high-gain Fabry-Perot antenna (FPA) based on the cancellation between the antenna mode RCS (AM-RCS) and structural mode RCS (SM-RCS). The ports of the two back-fed microstrip array antennas are connected to form the partial reflective surface (PRS) with a high reflectivity. The phase delay line (PDL) is proposed to control the AM-RCS to cancel out the SM-RCS. The AM-RCS is used to further reduce the in-band RCS of the low RCS high-gain FPA instead of being eliminated by the matched load. The measured results show that the FPA has a great impedance matching within the band of 9.8-11.2 GHz, and the maximum realized gain of the FPA reaches 10.7 dBi. The simulated bistatic RCS of the FPA is less than-14 dBsm within ±90 degrees angle domain at the center frequency. The minimum monostatic RCS of the proposed FPA is reduced by 17.9 dB compared with the reference FPA. Furthermore, this paper provides a design basis for the feed line length of the FPA from the perspective of scattering performance. INDEX TERMS Antenna mode radar cross section (AM-RCS), Fabry-Perot antenna (FPA), dividing scattering field, radar cross section (RCS).

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