The "E" model SPARQ units includes a switch matrix contain interconnected 40GHz mechanical switches. The switches route the TDR pulser/sampler and TDT sampler to pairs of ports during the DUT measurement phase, and to the internal O, S, L, T standards during the calibration phase of the measurement sequence. It is by virtue of the switch matrix that the OSLT calibration and S-parameters measurements can be taken without disconnecting or reconnecting a single adapter or cable. Each position of each switch has a rated lifetime of 2,000,000 actuations or throws, which is equal to about 600,000 4-port measurements. The rated lifetime of the switches are based on insertion loss, as opposed to mechanical failure.
One followup FAQ is "Why does the SPARQ not use solid state relays (SSRs)?" The reason is that SSRs are active non-linear devices, and will distort the signals that pass through them. The fact that they are active also complicates the calibration process; all components that drift should be behind the calibration reference plane, which would not be possible when using SSR's.