Flat-plate antennas have a compact form by use of a folded path network construction whereby received signals are coupled through a unitary network structure to an adjacent signal processing unit. On a folded path basis, processed signals are then coupled back into the network structure, combined with other received processed signals and then passed out of the network structure to an adjacent signal port. The signal processing unit may provide either amplification, phase shifting, or both. By reciprocal operation a signal to be transmitted may be divided into sub-array components, processed (e.g., power amplified and phase shifted), further divided, and coupled to each slot radiating element (e.g., 256 slots) of an array of slot sub-arrays. The unitary network structure may be formed of a stack of aluminum layers or plates, each having openings formed therein so that when the plates are stacked together normal and transverse waveguide sections are formed internally in an arrangement to provide signal coupling, combining and dividing. Methods employing folded path processing are also disclosed.