Measuring plasma wave properties with spatially separated antennae observes wavelength, propagation speed, and direction as well as frequency. This approach has been pivotal to progress in understanding three phenomena in space plasmas. The first is lower hybrid solitary waves, which are waves with cylindrical symmetry propagating inside a density cavity. The second is electron phase-space holes, which are propagating vortices in phase space. The third is called broadband ELF (extra low frequency) electric fields and is an important but poorly understood wave process essential to transverse ion acceleration.