  Radio interferometry most commonly involves antennas or antenna arrays of
identical design. The identical antenna assumption leads to a convenient and
useful mathematical simplification resulting in a scalar problem. An
interesting variant to this is a "hybrid" interferometer involving two designs.
We encounter this in the characterization of low-frequency antenna/array
prototypes using a homogenous low-frequency array telescope such as the
Murchison Widefield Array (MWA). In this work, we present an interferometry
equation that applies to hybrid antennas. The resulting equation involves
vector inner products rather than scalar multiplications. We discuss physical
interpretation and useful applications of this concept in the areas of
sensitivity measurement and calibration of an antenna/array under test using a
compact calibrator source.
