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The two-dimensional problem of acoustic scattering of an incident plane wave by a
semi-infinite array of either rigid or soft circular scatterers is solved. Solutions to the corresponding
infinite array problems are used, together with a novel filtering approach, to enable accurate solutions
to be computed efficiently. Particular attention is focussed on the determination of the amplitude
of the Rayleigh–Bloch waves that can be excited along the array. In general, the far field away
from the array consists of sum of a finite number of plane waves propagating in different directions
(the number depending on the observation angle) and a circular wave emanating from the edge of
the array. In certain resonant cases (characterised by one of the scattered plane waves propagating
parallel to the array), a different far field pattern occurs, involving contributions that are neither
circular waves nor plane waves. Uniform asymptotic expansions that vary continuously across all of
the shadow boundaries that exist are given for both cases.