  This paper proposes two spoof surface plasmon polariton (SSPP) leaky-wave
antennas using periodically loaded patches above perfect electric conductor
(PEC) and artificial magnetic conductor (AMC) ground planes, respectively. The
SSPP leaky-wave antenna is based on a SSPP transmission line, along which
circular patches are periodically loaded on both sides to provide an additional
momentum for phase matching with the radiated waves in the air. The PEC and AMC
ground planes underneath the antenna reflect the radiated waves into the upward
space, leading to an enhanced radiation gain. Both PEC- and AMC-grounded
antenna prototypes are fabricated and measured in comparison with the one
without any ground plane. The experimental results show that the PEC and AMC
ground planes increase the radiation gain by approximately 3 dB within the
operational frequency range 4.5-6.5 GHz. It also demonstrates that the
AMC-grounded leaky-wave antenna, with a thickness of 0.08\lambda at 6 GHz,
features more compact profile than the PEC-grounded one (with a thickness of
0.3\lambda at 6 GHz).
