REG NASA-LLIS-0770--2000 Lessons Learned RF Breakdown Characterization.pdf

1、Best Practices Entry: Best Practice Info:a71 Committee Approval Date: 2000-04-06a71 Center Point of Contact: JPLa71 Submitted by: Wilson HarkinsSubject: RF Breakdown Characterization Practice: Tests are performed to verify that radio frequency (RF) equipment, such as receivers, transmitters, diplexe

2、rs, isolators, RF cables, and connectors, can operate without damage or degradation. Reliability assurance is necessary in both a vacuum environment and at critical pressure with adequate demonstrated margins above the expected operating RF signal levels.Abstract: Preferred Practice for Design & Tes

3、t. Flight hardware may be damaged if operated at critical pressure or in a vacuum above the RF power levels at which the RF breakdown or multipaction phenomena occur. The damage may not be readily observable from external inspection of the hardware. Tests are performed to verify that radio frequency

4、 (RF) equipment, such as receivers, transmitters, diplexers, isolators, RF cables, and connectors, can operate without damage or degradation. Reliability assurance is necessary in both a vacuum environment and at critical pressure with adequate demonstrated margins above the expected operating RF si

5、gnal levels.Programs that Certify Usage: This practice has been used on Voyager, Galileo, CassiniCenter to Contact for Information: JPLImplementation Method: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-This Lesson Learned is based on Reliability

6、Practice number PT-TE-1432 from NASA Technical Memorandum 4322A, NASA Reliability Preferred Practices for Design and Test.Knowledge of the dielectric breakdown characteristics of RF devices at low pressures or in a near vacuum environment can be used to protect sensitive flight equipment. RF breakdo

7、wn is a concern because of the low, near-vacuum pressures at which spacecraft are tested and operated. RF breakdown testing is conducted to establish hardware resilience to the application of out-of-spec input signal levels, signal reflections due to mismatches at hardware interfaces, inadvertent ev

8、acuation of vacuum chambers during RF input, application of RF signals during the ascent phase of the spacecraft launch vehicle, etc.Implementation Method:Provide the expected signal level, plus an additional 6 dB over the expected operating frequency range, to the input of the device under test whi

9、le monitoring the output frequency. Reduce the atmospheric pressure from ambient to vacuum at the controlled rate specified in the test plan. After dwelling at vacuum for a period of time sufficient to monitor the performance of the unit under test, increase the atmospheric pressure from vacuum back

10、 to ambient at a controlled rate.After the test has been completed, inspect the test article for damage. Hardware damage is manifested by a change in the monitored RF performance during the test, or by visible indicators such as burn marks on output connectors. If neither indication is evident, the

11、equipment is considered to have passed the test. However, if the RF output signal dips or degrades, or external burn marks are seen, the test article is dismantled and inspected for internal burn marks in the vicinity of RF conductors. The typical corrective action is to redesign the equipment to pr

12、ovide wider gaps between RF signal conductors.Technical Rationale:Electrical damage to equipment or devices can occur due to dielectric breakdown. RF energy produces stress on the electrons in the gaseous medium between two electrodes situated within an electrical field. The RF breakdown phenomenon

13、occurs at low pressure when an RF field generates a sufficiently high voltage potential for the gas in the gap between two electrodes to ionize and transition from an insulator to a conductor. This happens when the production of electrons in the intermediary gas exceeds the removal of electrons. The

14、 two main mechanisms are:1. Ionization Breakdown: Ionization by electron collision is the dominant electron production mechanism. Ionization of the gas by electron collision happens at higher ambient pressures when the electron mean free path becomes shorter than the electron separation distance.2.

15、Multipaction: Multipaction, or secondary electron emission from the electrodes, occurs when the ambient pressure is sufficiently low that the electron mean free path is longer than the electron separation distance. Multipaction is observed at pressures below 10-2Torr.Provided by IHSNot for ResaleNo

16、reproduction or networking permitted without license from IHS-,-,-As a result, damage can occur in the small gaps between conductive or dielectric surfaces which may result in serious degradation of hardware performance. To establish the available margins for safe operation of the hardware prior to

17、spacecraft-level testing or launch, validate the RF power levels below which no damage will occur either in vacuum or at critical pressure.References1. Woo, R., “Final Report on RF Voltage Breakdown in Coaxial Transmission Lines,“ NASA Technical Report No. 32-1500, October 1, 1970.2. Radiated Suscep

18、tibility System Verification, Reliability Preferred Practice No. PD-TE-1416.Impact of Non-Practice: The hardware may be damaged if operated at critical pressure or in a vacuum above the RF power levels at which the RF breakdown or multipaction phenomena occur. The damage may not be readily observabl

19、e from external inspection of the hardware.Related Practices: N/AAdditional Info: Approval Info: a71 Approval Date: 2000-04-06a71 Approval Name: Eric Raynora71 Approval Organization: QSa71 Approval Phone Number: 202-358-4738Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-