Abstract: A signal processing apparatus for providing accurate electrical phase difference measurement of multiple concurrent signal inputs is disclosed. Phase measurement of an individual signal input is accomplished utilizing an efficient spatial sampling scheme. In operation, measurement and reference wideband RF inputs, differing primarily in phase over frequency, are respectively applied to two RF Channelizer components. Each Channelizer separates the composite input bandwidth into multiple time-coincident frequency output channels. Corresponding pairs of output channels then phase modulate a common independent carrier which propagates to the detection plane of a photodetector array forming a spatial interference pattern along one axis for each frequency channel number. A preferred detector element scaling relative to the interference pattern affords efficient phase difference measurement incorporating three detector elements at each frequency channel.