Power Combining

Abstract

Power amplifiers are employed in a variety of system applications, where the required power levels are largely different, varying from mW to kW [1,2]. Consequently, a wide variety of PA realizations results, from travelling-wave tube amplifiers in very high power systems [3,4], in satellite payloads or radars, to solid-state amplifiers for medium-low power systems [5,6], such as wireless communication handsets. The request for high output power levels is influencing device technologies adopted for PA module realization [7,8]. Prior to the development of solid state devices, microwave power amplification and generation were mainly based on the use of vacuum tubes [9, 10], including magnetron, klystron and travelling-wave implementations (TWTAs) [4,11]. These devices still remain in use at kilowatt levels, where solid-state devices cannot compete so far.Nevertheless, the development of high power microwave solid-state device technologies (GaAs HEMT or HBT, GaN HEMT, etc.) may offer an order-of-magnitude improvement in reliability and reduction in size, weight, and low-voltage power-supply requirements as compared to vacuum devices. However, the output power attainable from a single solid-state device is basically limited by thermal and impedance matching problems. To meet system requirements it is therefore mandatory to combine several devices, thus attaining higher power levels. Many power splitting/combining schemes have been investigated and developed, involving different technologies and propagation media, ranging from metal waveguides (cavities, microstrips, striplines, etc.) where the power is confined into a limited region, to open space configurations [12][13][14].Devices involved in power splitting/combining operations are referred to as power splitters/ combiners and they play a key role in the design of high power PA, while being also fundamental components in designing mixers [15], multipliers and oscillators [16,17], or other linear and nonlinear circuits [18]. Moreover, since the proposed schemes can often be adopted for both the tasks of power division and combination, the terms power combining and power splitting are usually adopted simultaneously or interchangeably. Due to their intrinsic reciprocal characteristic in fact, the same device can alternatively be viewed as a power combiner or as a power splitter, depending on the selection of its input and output ports.The key features of power splitting/combining devices are clearly their insertion loss (related to the efficiency), bandwidth and size. The techniques adopted for the optimization of device performance are strictly related to the type of splitting/combining structure and to the selected realization technology. High Efficiency RF and Microwave Solid State Power Amplifiers

A 17.3–20.2-GHz GaN-Si MMIC Balanced HPA for Very High Throughput Satellites

“…A three-stage balanced architecture with input and output Lange coupler was selected. The use of the latter leads to a twofold benefit as compared to a more standard corporate topology [7]. First, the HPA return losses are minimized being almost coincident with those of the Lange structure.…”