High-altitude electromagnetic pulse survivability test study on shortwave receiving antenna system by pulsed current injection
To evaluate the threat of high-altitude electromagnetic pulse HEMP environment on a shortwave receiving antenna system, pulsed current injection tests for the front-end equipments near the antenna, including some commercial surge protection devices, have been conducted. Both a fast rise-time nanosecond square waveform pulser and a double exponential waveform pulser with high current output, are adopted to check the responses of various surge protection measures. Results show that three protection devices have played essential roles in preventing against HEMP conducted disturbance. Firstly a gas discharge tube at the end of the whip antenna breaks down within a few nanoseconds, since it suffers an overvoltage much higher than its nominal DC breakdown voltage. Then a transient voltage suppressor (TVS) in the commercial signal surge protection device also responses quickly to clamp the line voltage. And the amplifiers in the signal transmission equipments also limit the residual voltage of the disturbance propagating forward, as they are readily to enter the saturation mode under excess inputs. Therefore, the system can withstand either a fast rise-time nanosecond square waveform pulse with an voltage amplitude of 3.5 kV, or a double exponential (20/500 ns) waveform current pulse with an amplitude of 1.8 kA. The only effect is that the latter signal transmission equipment outputs a disturbance signal with a saturated amplitude ( 3 V) which lasts for several microseconds. This implies that , when combining the selected commercial surge protection devices properly, it is practicable to protect similar low working voltage antenna systems against both lightning electromagnetic pulse and HEMP.