The silicon PIN diode as a microwave radar protector at megawatt levels

A silicon PIN diode developed for use as a microwave protector promises to have considerably greater reliability than gas T-R tubes. The switching action of the device results from the lowering of I layer resistance by conductivity modulation, caused either by sufficiently high microwave power levels or by applied dc bias. A theoretical analysis is presented here which yields equations for I layer resistance as a function of excitation (dc bias or microwave power). Predictions are made about the relative effectiveness of direct current or microwave power in modulating the I layer; for example, 100 ma dc bias should produce about the same injected carrier concentration as 100 kw of microwave power at 1 Gc. An experimental X-band protector consisting of an appropriately tuned PIN diode connected across a waveguide presented to low level signals an insertion loss 1 db or less when zero biased, and an insertion loss of up to 34 db at 100 ma forward bias. Measurements of temperature rise in the wafer as a function of applied X-band power indicated that the diode could protect against microwave pulses with energies of up to 38 Mw-µsec before burnout, in good agreement with theoretical predictions.