This research concerns the investigation of applications of broadband and multiple band amplifier antenna arrays for spatial power combining systems. Spatial power amplifiers are used to combine power from an array of solid-state devices at millimeter-wave frequencies, resulting in increased output power, power combining efficiencies, and power added efficiencies. An array of antennas with active devices (microwave amplifiers) is excited with uniform field distribution (magnitude and phase), and power carried by the incident field is amplified and then reradiated by the output antennas. This power is combined in space due to coherent conditions for the magnitude and phase satisfied for each output antenna. Spatially distributed power combining systems generally consist of a number of transverse electric and magnetic layers (for example, a patch antenna array coupled to a slot antenna array) separated by waveguide sections. The idea of a generalized scattering matrix (GSM) is utilized for the simulation of large waveguide-based electromagnetic power combiners, wherein an entire system is decomposed into individual modules. The GSM of each module is obtained based on a full-wave analysis technique (in particular, integral equation method and finite-difference time-domain method), and the overall system response is obtained by cascading GSMs of individual modules. The GSM is constructed for all propagating and evanescent TE- and TM-modes and provides an accurate account of the interactions between neighboring modules.
      New types of antennas such as, tapered meander line, U-slot patch, microstrip loop, triangular slot antennas and their modifications are proposed as receive and transmit elements of antenna arrays to increase frequency bandwidth, create conditions to operate in multiple band regimes, and increase radiating and power combining efficiency of the system. Multilayered dielectric environment containing interacting antenna arrays is used to suppress surface-wave effects and optimize operational frequency bands of the system.