Passive signal combiners are employed to transform at least one signal from one domain to another. In some aspects the transformation comprises an FFT, an IFFT, a DFT, or an IDFT. In some implementations the passive signal combiners comprise a set of planar waveguides (e.g., which may be referred to as beamformers or Rotman lenses) that have multiple inputs and outputs and are configured to provide orthogonal output signals. In some implementations an electrical signal (e.g., received via an antenna element) is coupled to passive beamformers that transform the electrical signal from one domain to another domain. Here, a transformation of the electrical signal by a given passive beamformer may have a first resolution, and outputs from the passive beamformers may correspond to orthogonal groups. A combiner circuit may be used to combine the outputs from the passive beamformers and produce a combined output having a second resolution and an associated error. In some aspects, this error may be less than a cumulative error associated with the passive beamformers if a single passive beamformer was instead employed to transform the electrical signal at the second resolution. Also, by using at least partially different bandwidths for components in the circuits, a higher effective bandwidth for the transformation may be achieved.