This paper proposes an ultra-wideband hybrid polarization conversion-absorption (PCA) metasurface with a transmission band for radar cross section (RCS) reduction application. To achieve the in-band transmission of the incident wave and the out-of-band suppression of the scattering wave, the proposed metasurface is composed of a low-frequency PCA array, a high-frequency polarization conversion (PC) array, and a second-order frequency selective surface (FSS). The lumped resistors are used in the PCA array to generate the absorption characteristic, thus giving rise to the reduction of the co-polarization component of the scattering field and meanwhile the elimination of the high-frequency resonances. An interdigital structure is introduced into the PCA array to not only achieve a good transmission for a co-polarization component of the incoming wave but also result in an extra PC band for narrowing the transition band between the transmission window and the high-frequency PCA band. The orthogonal layout of the PCA array and the PC array is used to decrease the interaction between them, thus resulting in an ultra-wideband PCA band. The second-order FSS consisting of a stacked structure is designed to generate a good passband with the steep roll-off and the good out-of-band suppression. The proposed metasurface has an ultra-wideband PCA band, a good transmission band, and narrow transition bands. When the proposed metasurface is arranged into an array in a rotation way, the ultra-wideband RCS reduction performance can be obtained. Simulated and measured results are given to demonstrate a 10 dB RCS reduction band of 3.4-24.6 GHz with a -1 dB transmission band of 8.45-10 GHz.

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