1. Field of the Invention
An object of the invention is a microwave switch, comprising an interference device, either arm of which is capable of undergoing a reversible transition from a normal state to a superconductive state, with the position of the switch depending on the respective state (normal or superconductive) of the two arms. A switch of this type can be advantageously applied to the making of duplexers for radar systems, microwave phase-shifters and microwave attenuators.
The characteristics of a microwave switch are notably:
its frequency (or its wavelength) of operation;
the width of the passband in which the operating frequency is located;
the nature and extent of the losses due to its presence along a microwave line, said presence being capable of introducing a partial reflection (measured by an SWR), losses by radiation and/or thermal losses, and a partial deflection of the energy transmitted along the line;
its switching-over time between an "on" state (corresponding to a closing of the switch) and an "off" state (corresponding to an opening of the switch), and reciprocally;
its power-handling capacity;
its dimensions, dependability, consumption and cost of manufacture.
2. Description of the Prior Art
There are known methods of using a PIN diode (adapted, as is known, to microwave signals) as a microwave switch: when subjected to a forward bias, it behaves like an "on" switch, and when a reverse bias is applied to it, it is similar to an "off" switch. However, as is known, the switching-over time of a diode of this type is limited, at the lower end, by the time needed to discharge the minority carriers (which are the carriers that most extensively contribute to the passage of a microwave current when the diode is forward biased). Furthermore, a PIN diode mounted on a microwave line introduces a spurious resistance in series (this is a phenomenon known to those skilled in the art). Finally, the power-handling capacity of a diode of this type is limited, at the upper end, by the value of the avalanche voltage of the diode.
There is also a known way to use a so-called TR tube as a microwave swich: (TR being an abbreviation of the term "transmit-receive": this type of tube indeed is often used in a radar antenna to insulate the receiver at transmission and prevent the propagation of signals towards the transmitter at reception). The switching-over time of tubes of this type is unfortunately limited, at the lower end, by the time needed for the discharge and/or elimination of ionized atoms and electrons. Furthermore, this relaxation phenomenon, as it is known, is only partial: the residual ionization of the gas contained in the tube damages the dependability of said switch.