RF switches are devices that route radio frequency signals to particular waveguides.  Important performance specifications to consider when searching for RF switches include the frequency range, insertion loss, isolation, switching speed, impedance, and VSWR.  The frequency range is the signal frequency range of the switch.  Insertion loss is the total RF power transmission loss resulting from the insertion of a device in a transmission line. It is defined as the ratio of signal power at the output of the inserted device to the input signal power at the input of the inserted device.  The isolation from port A to port B of a device is defined as the degree of attenuation of the signal at port A measured at the B port with all other ports properly terminated.  Isolation is expressed in dB.  The switching speed is the speed at which the switch can operate.  Impedance is typically either 50 ohms or 75 ohms.  When there are impedance mismatches in a system, some energy transmitted through will be reflected back to the source. Different amounts of energy will be reflected back depending on the frequency of the signal.   VSWR (Voltage Standing Wave Ratio) is a unitless ratio ranging from 1 to infinity, expressing the amount of reflected energy.  A value of one indicates that all the energy will pass through, while any other value indicates that a portion of the energy will be reflected.