An efficient arrangement of four switches has been conceived for coupling, to four output ports, the output powers of any subset of four devices that are members of a redundant set of five devices. In normal operation, the output power of each of four of the devices would be coupled to one of the four output ports. The remaining device would be kept as a spare: normally, its output power would be coupled to a load, wherein that power would be dissipated. In the event of failure of one of the four normally used devices, that device would be disconnected from its output port and connected to the load, and the spare device would be connected to the output from which the failed device was disconnected. Alternatively or in addition, the outputs of one or more devices could be sent to ports other than the ones originally assigned to them.

Figure 1. Ports A, B, C, and D can be connected in either of two different combinations of pairs,depending on the setting of a waveguide switch of the “baseball” type. Nominally equivalent switchingcould be effected by use of an electric circuit containing a DPDT switch.

In the original intended application, the devices would be microwave amplifiers and the switches would be mechanically actuated waveguide switches. The arrangement could also be generalized to devices other than microwave amplifiers, to switches other than mechanically actuated microwave switches, and to greater numbers of switches, ports, and devices (N, N, and N + 1, respectively, where N > 4).

The mechanically actuated microwave switches in the original application would be two-position, four-port switches of a type known in the art as “baseball switches” because of the resemblance between their waveguide cross sections and the patterns of stitches on baseballs. Figure 1 depicts the two positions of a baseball switch and the corresponding positions of a nominally equivalent circuit containing a double-pole, double-throw (DPDT) switch.

Figure 2. These Three Switching Configurations are a few examples of the larger number of allowable configurations for directing the outputs of four ofthe five amplifiers to the four output ports.

Figure 2 depicts three examples of useable switching configurations representative of the modes of operation described above. It should be apparent from casual inspection that any of those modes can be attained by actuation of one or more switches. In the original application and perhaps in other potential applications, safety considerations dictate that switching configurations be limited to those in which every amplifier is connected to either an output port or to the load; non-connection of an amplifier or connection of an amplifier to another amplifier is not allowed.

This work was done by James Lux and Robert McMaster of Caltech for NASA’s Jet Propulsion Laboratory.

This Brief includes a Technical Support Package (TSP).
Efficient Switching Arrangement for ( N + 1)/ N Redundancy

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This article first appeared in the October, 2007 issue of NASA Tech Briefs Magazine.

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