A long baseline interferometer antenna system and method for determining the location of an emitter. The long baseline interferometer antenna system comprises a first antenna, a second antenna, an inertial navigation system, an antenna baseline measurement system, a multi-channel receiver and a processor. The first and second antenna elements are positioned on a platform and are both configured to receive signals from the emitter. The first and second antenna elements form a long baseline antenna pair. The inertial navigation system measures the platform position and attitude; and the antenna baseline measurement system measures the antenna baseline vector between the first and second antenna elements. The multi-channel receiver measures the differential phase between antenna pairs, and the processor computes the emitter location. Additional antenna elements can be included and some can be configured as squinted beam pair and make use of amplitude difference of arrival measurements.