  In this paper, we combine the design of band-pass frequency selective
surfaces (FSSs) with polarization converters to realize a broadband
frequency-selective polarization converter (FSPC) with lowbackward scattering,
which consists of the top polarization conversion layer backed by a multi-layer
bandpass FSS. It is numerically demonstrated that the 1 dB transmission window
can be obtained from 8.5 GHz to 11 GHz with a 25.6% fractional bandwidth (FBW),
and the bandwidth of reflection below -10 dB is up to 92% from 5.6 GHz to 15.13
GHz. Moreover, the proposed device can achieve two polarization conversion
bands (5.66-6.9 GHz and 12.8-15.2GHz) with the polarization conversion ratio
over 90%. Besides, by arranging the proposed structure in a checkerboard-like
distribution, the backward scattering energy can be reduced in a wide frequency
band ranging from 4 to 16 GHz. Both simulation and experimental results are in
good agreements, which demonstrates our design strategy. Compared with the
conventional polarization conversion designs, the proposed design presents an
extra frequency-selective performance and hence can be applied to various
practical situations, for instance, working as radomes to transmit the in-band
signals with high-efficiency while keeping low-backward scattering for the
out-of-band waves.
