Pre-Compliance EMC Testing of an Automotive Navigation System (CISPR 25 Bench Setup)

This case study describes a pre-compliance EMC test campaign on an automotive navigation subsystem designed to support high-level autonomous driving functions. The unit integrates LiDAR and radar sensors and was evaluated using a CISPR 25-based bench-top setup to assess conducted emissions, radiated emissions, conducted immunity (BCI), and ESD before formal lab testing. By combining current-probe measurements, TEM cell predictions, and bulk current injection testing, we were able to identify early EMC behaviours and give confidence in the design’s ability to meet regulatory requirements.

Client Context

The client is an automotive Tier‑1 supplier developing a cutting‑edge navigation subsystem intended to support high‑level autonomous driving functions. The unit integrates LiDAR and radar sensors and is designed to operate as part of a larger autonomous driving platform. A camera is not included in this module, as it will ultimately be integrated into a higher‑level system that provides the full sensor suite required for autonomous operation.

Scope of Work

The scope of this engagement was clearly defined. The client asked us to carry out an automotive component / subsystem‑level EMC pre‑compliance assessment.

The objective was to gain an early understanding of the EMC performance of the unit without immediately progressing to full laboratory compliance testing.

This approach helps to:

• Identify potential EMC risks early

• Highlight any red‑flag issues at an early design stage

• Reduce cost and time associated with late‑stage compliance failures

• Enable targeted design improvements ahead of final certification testing

The specific tests of interest were:

• Conducted emissions

• Radiated emissions

• Conducted immunity (Bulk Current Injection – BCI)

• Electrostatic discharge (ESD)

Technical Approach

A CISPR 25–based automotive EMC bench‑top test set-up was established in our laboratory to replicate key elements of a vehicle‑level EMC environment.

To assess radiated emissions efficiently at the pre‑compliance stage, we employed a hybrid measurement approach, combining:

• Current probe measurements on cables

• TEM cell testing

This methodology allows far‑field radiated emissions behaviour to be predicted with good confidence, without the need for a full anechoic chamber.

For conducted immunity, we carried out Bulk Current Injection (BCI) testing on cables using our in‑house setup, enabling early identification of susceptibility risks.

Summary

• We tested the DUT using a quasi-CISPR25 automotive set-up. Since the power supply cable is relatively long—and we intend to use this length later for radiated emissions testing—we decided to leave it as is.

• The conducted emissions results were promising, with the DUT appearing to meet Class 5 limits. Even if not, achieving Class 4 should be very realistic. The uncertainty here comes from the differences in the test set-up (long cable rather than a short cable that is less than 20 cm).

• For radiated emissions (up to 1 GHz), we used both an RF current probe and a TEM cell. No red flags were observed at this stage, and the DUT is expected to meet ECE Regulation 10 requirements. Compared to CISPR 25, we believe

compliance with Class 3 or 4 should also be achievable.

• We tested two configurations: one with the DUT placed on a 50 mm insulation support over the test ground plane, and the other with the DUT chassis directly placed on the ground plane. From a conducted emissions standpoint, the results were very similar—an encouraging sign. Radiated emissions are expected to improve further with the direct bond to the ground plane.

• For immunity testing, we performed BCI (Bulk Current Injection) while monitoring the data packets for signs of corruption or loss—none were observed. We also used a current monitoring probe to track injected current, as the set-up introduces VSWR on the cable. During testing, the minimum injected current was around 50 mA, with an average level above 70 mA, providing good confidence in the DUT's immunity performance.