  We predict magnon polariton states circulating unidirectionally in a
microwave cavity when loaded by a number of magnets on special lines. Realistic
finite-element numerical simulations, including dielectric, time-dependent and
non-linear effects, confirm the validity of the approximations of a fully
analytical input-output model. We find that a phased antenna array can focus
all power into a coherent microwave beam with controlled direction and an
intensity that scales with the number of magnets.
