Required amplifier power in automotive radar pulse measurements: what will keep your brakes from failing or your airbag from deploying the next time you cruise past an airport?(EMC APPLICATIONS)

For many years, automakers have performed electromagnetic compatibility testing of automobiles before their release to consumers. However, as the electronics content of vehicles becomes greater every year, it expands the potential for component or system failure caused by external sources of electromagnetic radiation.

One challenge has come from commercial and military airport radar systems that operate at frequencies from 1.2 to 1.4 GHz and 2.7 to 3.1 GHz. Cases have been reported in which vehicles near airports and military bases suffered degradation or even failure of critical vehicle systems including braking controls and airbag deployment. As a result, Ford Motor Company and General Motors Worldwide (GMW) have introduced sections in their immunity standards for component testing when exposed to radar pulses, such as those at the 600-V/m level.

Generating pulsed RF signals at such an elevated power level and frequencies for EMC testing requires the use of high-power amplifiers and very-high-gain antennas. Since the cost of RF power escalates with increasing frequency, it is important to subcontractors and test houses that the amount of RF power required be as low as possible.

The principal method of making these measurements is with an absorber-lined shielded enclosure (ALSE) and a test bench with a metallic ground plane. However, there is an alternate method using a reverberation chamber (RVC).

The Standards

The standards that guide the EMC testing of automotive components for GMW and Ford are GMW 3097 and ES-XW7T-1A278-AC, respectively. The radiated immunity test set for each one is based on ISO-11452-2.

The previous version of the GMW and Ford tests considered only one severity level, 600 V/m, and required 50 3-[micro]s pulses within a 1-s period at a repetition rate of 300 Hz. At present, GMW still requires the 50 pulses within a second, but Ford removed this specification, leaving just the pulse repetition rate of 300 Hz and pulse duration of 3 [micro]s.

GMW and Ford specify testing from 1.2 to 1.4 GHz, and Ford requires testing from 2.7 to 3.1 GHz as well. Recent revisions by Ford eliminated the need for a metallic ground plane, replacing it with a test bench that has a low dielectric constant and height of 1 m [+ or -]50 mm. …

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