Abstract: The in-band radar cross section (RCS) of antenna can be reduced by high impedance surface (HIS) due to the reflection phase band-gap. For the basic square HIS, one size has only one reflection phase band-gap. Dual reflection phase band-gap HIS structure is realized by the method of different parameters cascading in this paper, and the cascaded HIS structure is fabricated on the dual-band antenna to reduce the RCS. The simulation and measured results show that compared with the original antenna the in-band RCS of the U-shape dual-band antenna is reduced by at least 15dB at lower frequency and 5dB at higher frequency.