Active solid state receiver protection

Externally driven PIN diodes are often used to protect sensitive radar receivers from high power transmitters. The diodes in these active protectors are biased by a pulse which completely overlaps the radar transmission pulse, thus protecting the receiver against the radar's own transmitter but not against unsynchronized high power signals. The latter phenomenon is generally not a problem, however, since RF filtering reduces the unsynchronized pulses to acceptably low levels. The diodes of the protector are mounted by a coaxial stub or folded method, i.e., they are mounted at the end of a short coaxial line coupled into the waveguide by a boss and post structure. Using this structure, the effective impedance of the mount and diode can be modified by changing the boss height, length of coaxial line, or post diameter. The PIN receiver protector operates in three modes: normal, fault, and passive. High performance is generally achieved in terms of insertion loss, isolation, plus leakage. The design and performance of a practical 10 cm-band active PIN diode protector are described. In the reverse biased condition, the VSWR was better than 1.2:1, and the insertion loss better than 0.4 dB; the peak power capacity has been checked to 50 kW.