This article describes the spatial power combining techniques dealing with the state of the art of Spatial Power Combiners (SPC) considering recent developments. A brand- new splitting scheme is proposed where difierent types of SPC are grouped according to the space where power combining and splitting occur. This paper should provide compendium knowledge for SPC design and selection of the opportune SPC basing on the target application. 1. INTRODUCTION In airborne and space applications, characteristics like reliability, size, e-ciency and weight of the Power Ampliflers (PA) assume a very important role in the selection of the proper PA to be employed. High RF power levels are demanded to vacuum tubes ampliflers like TWTA, Klystron or Gyrotrons but those have the main disadvantage to use heated wires and bulky magnets or electromagnets that give greater size and weight and reduce e-ciency (1). So, combined Solid State PA (SSPA) would be greatly appreciated if they could give at least the same order of magnitude in RF power levels, since in this case graceful degradation is increased. Spatial power combining technique is an alternative one to combine many SSPA reducing to a minimum extent the combining losses (2{4). This article deals with the state of the art of Spatial Power Combiners (SPC) and their charac- teristics (14). In addition, it is proposed a new splitting scheme for the SPC family, grouped respect to the ambient where combining and splitting take place, as shown in Figure 1. The fundamental SPC Amplifler's concept is to provide a large power value with minimum losses. In SPC the elec- tromagnetic energy coming from input is divided as much as possible in the space, without using transmission lines, and it is sent to many SSPA's. After amplifled energy is collected, it is sent to output port with the lowest possible number of transmission lines. SPC employees probes, antennas or transitions to take the spatial RF energy and send it to a two wires transmission line: the use of connectors at the ampliflers ports exclude the combiner to belong to the class of SPC. The system's quality is usually determined from its e-ciency. SPC e-ciency can be deflned as how much power is sent to ampliflers respect to how much power is provided to input port, such as it quantifles the capability of the combiner to intercept incoming energy PI and distribute it to N energy dividing/combining internal ports, that is
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