Diode bridge switching circuit with high attenuation

A signal generator including a source of high frequency signals having a regulated amplitude level;

• and a switching circuit arranged to receive and derive from said high frequency signals a pulse modulated signal, said switching circuit including a first switchable four-arm diode bridge connected between an input port for receiving said signals and an output port for delivering a pulse modulated signal, a second switchable four-arm diode bridge conntected to said input port in shunt with said first bridge;
• impedance matching means for presenting a predetermined matched value to said input port whilst said second bridge is conductive;
• attenuation means for attenuating any high frequency signal breaking through said first diode bridge whilst in a non-conductive state, said means including a third switchable four-arm diode bridge connected in shunt with said first between said output port and a reference potential level, said third bridge having a conductive state controlled in step with said second bridge to correspond therewith;
• and means connected to said bridges for controlling the conductive states of said first and second bridges os that said first bridge is conductive whilst said second bridge is non-conductive and vice versa.