  We investigate coherent single-photon transport in a waveguide quantum
electrodynamics structure containing multiple giant atoms. The single-photon
scattering amplitudes are solved using a real-space method. The results give
rise to a clear picture of the multi-channel scattering process. In the case of
identical and equally-spaced giant atoms in a separate configuration, we also
use the transfer-matrix method to express the scattering amplitudes in terms of
compact analytical expressions, which allow us to conveniently analyze the
properties of the scattering spectra. Based on these theoretical results, we
find that the non-dipole effects of giant atoms, which are relevant to the
design of the setup, can strongly manipulate several types of collective
properties of the output fields, including the superradiant phenomenon, the
multiple Fano interference, and the photonic band gap. This makes it possible
to manipulate the photon transport in a more versatile way than with small
atoms. We also make a proposal to probe the topological states of a chain of
braided giant atoms by using photon scattering spectra, showing that waveguide
quantum electrodynamics systems with giant atoms are ideal platforms to merge
topological physics and on-chip quantum optics.
