Not applicable to this invention.
The present invention concerns a power combining system and in particular concerns a fault-tolerant power combining system.
Power combining networks are used to combine the power generated by a group of amplifiers into a single output. Power combining networks provide solutions for many applications that require more output power than can be provided using a single conventional amplifier. For example, power combining networks are commonly used to broadcast signals in satellite communication systems such as Satellite Digital Audio Radio Service (SDARS) systems and Direct Broadcast Satellite (DBS) systems.
A significant advantage of a power combining network is the ability of the network to compensate for amplifier failure. Typical power combining network designs, especially those used in satellite communication systems, include redundant amplifiers. For example, an eight-amplifier system such as that shown in
A problem arises when the number of amplifier failures exceeds the number of redundant amplifiers in the system. In an ideal system, the power loss (in dB) of an N-input system in this situation is
where N is the number of amplifier inputs in the system and m is the number of failed amplifiers (with m<=N−1). However, the power loss suffered by a conventional system is significantly greater than that of an ideal system. This difference is better understood by examining the operating characteristics of network 10 depicted in
Power combiner 14 is typically implemented using a four-port waveguide power combiner to handle the power necessary for most satellite applications. Signals fed into the two input ports of power combiner 14 constructively combine into a single signal. If the two signals are appropriately phased with respect to each other, a single signal with twice the power is output from one of the output ports. If the two signals are not phased correctly with respect to each other, a portion of the output power is diverted to load 16 attached to the other output port. When an amplifier fails, and therefore does not provide a signal to one of the input ports, an ideal system would pass the power of the signal of the operational amplifier connected to the power combiner through to the next stage of power combiners. However, in a conventional system a significant portion of that power is diverted into load 16. Accordingly, the power loss (in dB) from one or more failed amplifiers in a conventional N-input system is
where N is the number of amplifier inputs in the system and m is the number of failed amplifiers (with m<=N−1).
Accordingly, a need exists for a new power combining network design. The new power combining network should improve network efficiency and recover more power in the event of amplifier failure. Furthermore, the new power combining network should be cost effective and minimize any additional hardware required.
The present invention addresses the foregoing deficiencies of conventional power combining networks by providing a fault-tolerant power combining system. Using short plates and reactive combiners, the invention recovers a significant portion of the power lost in conventional systems upon failure of one or more amplifiers. In particular, short plates are used to redirect power reflected out of the reactive combiners back into the reactive combiner to be combined with the signal input into the reactive combiner by a functioning amplifier. In this manner, a significant portion of power lost using conventional power combining networks is recovered using a minimal amount of additional hardware.
According to one aspect of the invention, a power combining system includes multiple amplifiers, a reactive combiner for combining the output power of the amplifiers and a short plate. Switches are used to electrically connect an output of each of the amplifiers to an input of the reactive combiner. In addition, switches are used to electrically connect the short plate to an input of the reactive combiner in place of a failed amplifier.
According to another aspect of the invention, a power combining system includes multiple amplifiers, multiple power combiners for combining the output power from the amplifiers, and short plates. The power combiners are arranged in stages, with the power combiners used in the first stage being reactive combiners. Switches are used to electrically connect the output of each of the amplifiers to a respective input of a reactive combiner in the first stage of power combiners. Switches are also used to electrically connect a short plate to an input of a reactive combiner in place of a failed amplifier.
Preferably, the multiple amplifiers amplify a common signal in parallel. It is also preferable that the electrical path length between the short plate and the reactive combiner allow a signal reflected by the short plate back into the reactive combiner to be in phase with respect to a second signal input into the reactive combiner. Finally, isolators preferably isolate the amplifiers and redirect power reflected by the reactive combiner into a load connected to the respective isolator.
The foregoing summary of the invention has been provided so that the nature of the invention can be understood quickly. A more detailed and complete understanding of the preferred embodiments of the invention can be obtained by reference to the following detailed description of the invention together with the associated drawings.
The output of each amplifier 21 is coupled to a first stage of power combiners via a redundancy switch 24. Unlike conventional systems, the first stage of power combiners is made up of reactive combiners 25. In this embodiment of the invention, the latter two stages of power combiners are made up of four-port power combiners 26, with their respective loads 27, as in conventional systems. However, alternative embodiments of the invention include implementations using reactive combiners 25 in one or more of the latter stages of power combiners.
Network 20 also includes one or more redundant amplifiers, which are represented by redundant amplifier 30 depicted in
Isolators 22, redundancy switches 24, reactive combiners 25, four-port combiners 26 and short plate switches 28 are implemented using waveguides according to one embodiment of the invention. The materials and size of the waveguides used are dependent upon the frequency bandwidth of the signal being amplified and combined by network 20. The design of appropriate waveguides to be used in the individual components is well known to those of ordinary skill in the art and will not be described herein.
The operation of the present invention will now be described with reference to
To maximize recovery of lost power, the electrical path length between short plate 29 and reactive combiner 25 is designed so that the reflected signal power reaches reactive combiner 25 properly phased with respect to the signal power output by operational amplifier 21b. This electrical path length is determined based on factors such as the frequency bandwidth of the signals being output and the design of reactive combiner 25, which are well known to those skilled in the art. In a perfectly efficient system, the signal power output by reactive combiner 25 will equal that of operational amplifier 21b.
The foregoing description of the invention described a two-input power combining network 20a. The eight-input power combining network 20 depicted in
As described above, the present invention provides a fault-tolerant power combining system which recovers and outputs more signal power in the event of amplifier failure than conventional power combining systems. According to the invention, the power loss (in dB) in an N-input power combing network is
where N is the number of amplifier inputs to the system and m is the number of failed amplifiers (with m<=N−1). Returning to
The foregoing detailed description of the invention is intended to illustrate preferred embodiments of the invention. However, the examples set forth above are not intended to limit the scope of the invention, which should be interpreted using the claims provided below. It is to be understood that various modifications can be made to the illustrated examples of the invention without departing from the spirit and scope of the invention.
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