  We present the optical characterization of two-scale hierarchical
phased-array antenna kinetic inductance detectors (KIDs) for
millimeter/submillimeter wavelengths. Our KIDs have a lumped-element
architecture with parallel plate capacitors and aluminum inductors. The
incoming light is received with a hierarchical phased array of slot-dipole
antennas, split into 4 frequency bands (between 125 GHz and 365 GHz) with
on-chip lumped-element band-pass filters, and routed to different KIDs using
microstriplines. Individual pixels detect light for the 3 higher frequency
bands (190-365 GHz) and the signals from four individual pixels are coherently
summed to create a larger pixel detecting light for the lowest-frequency band
(125-175 GHz). The spectral response of the band-pass filters was measured
using Fourier transform spectroscopy (FTS), the far-field beam pattern of the
phased-array antennas was obtained using an infrared source mounted on a 2-axis
translating stage, and the optical efficiency of the KIDs was characterized by
observing loads at 294 K and 77 K. We report on the results of these three
measurements.
