  Highly integrated active nanophotonics addressing both device footprint and
operation speed demands is a key enabling technology for the next generation
optical networks. Plasmonic systems have proven to be a serious contender to
alleviate current performance limitations in electro-optic devices. Here, we
demonstrate a plasmonic optical phased array (OPA) consisting of two
10-$\mu$m-long plasmonic phase shifters, utilized to control the far-field
radiation pattern of two subwavelength-separated emitters for aliasing-free
beam steering with an angular range of $\pm5^\circ$ and flat frequency response
up to 18 GHz (with the potential bandwidth of 1.2 THz). Extreme optical and
electrostatic field confinement with great spatial overlap results in high
phase modulation efficiency ($V_{\pi}L=0.24\: \text{Vcm}$). The demonstrated
approach of using plasmonic lithium niobate technology for optical beam
manipulation offers inertia-free, robust, ultra-compact and high-speed beam
steering.
