We report on the measurement of topological invariants in an electromagnetic
topological insulator analog formed by a microwave network, consisting of the
winding numbers of scattering matrix eigenvalues. The experiment can be
regarded as a variant of a topological pump, with non-zero winding implying the
existence of topological edge states. In microwave networks, unlike most other
systems exhibiting topological insulator physics, the winding can be directly
observed. The effects of loss on the experimental results, and on the
topological edge states, is discussed.Comment: 10 pages, 10 figure
