  This paper proposes a bidirectional multibeam hybrid transmitarray (HTA)
employing a transmission polarization-rotating metasurface (TPRM). A novel
configuration is introduced to facilitate bidirectional beam scanning by
combining the transmitarray (TA) and folded-transmitarray (FTA). To accomplish
the reconfiguration of both unidirectional and bidirectional radiation states
in the +z, -z, and +/-z directions, a polarization switchable multi-feed array
(MFA) is placed at the focal plane between the TA and FTA, radiating
x-polarization, y-polarization, and 45-degree oblique polarization waves,
respectively. Meanwhile, the proposed antenna can achieve multibeam radiation
in the three aforementioned states by switching the polarization of the MFA. To
demonstrate the operating principle, a prototype has been designed, simulated,
and fabricated. The measured results agree well with the simulated results. The
simulated and measured results indicate that the proposed design can generate
reconfigurable multibeam in both forward and backward directions, either
separately or simultaneously. In the unidirectional states, forward and
backward beam scanning is achieved within an angular range of +/-30{\deg} and
+/-22{\deg}, respectively, with peak gains of 23.6 dBi and 23.1 dBi. A
simultaneous forward and backward beam scanning of +/-40{\deg} and +/-22{\deg}
is achieved in the hybrid radiation state, with peak gains of 19.4 dBi and 19.3
dBi, respectively. The proposed antenna array design offers several advantages,
including bidirectional low-loss beam scanning, a simple structure, low power
consumption, and a low profile.
