  Photonic topological insulators are an interesting class of materials whose
photonic band structure can have a bandgap in the bulk while supporting
topologically protected unidirectional edge modes. Recent studies [1-6] on
bianisotropic metamaterials that emulate the electronic quantum spin Hall
effect using its electromagnetic analog are examples of such systems with
relatively simple and elegant design. In this paper, we present a rotating
magnetic dipole antenna, composed of two perpendicularly oriented coils, that
can efficiently excite the unidirectional topologically protected surface waves
in the bianisotropic metawaveguide (BMW) structure recently realized by Ma, et
al. [1], despite the fact that the BMW medium does not break time-reversal
invariance. In addition to achieving high directivity, the antenna can be tuned
continuously to excite reflectionless edge modes to the two opposite directions
with various amplitude ratios. We demonstrate its performance through
experiment and compare to simulation results.
