In electromagnetic compatibility (EMC) immunity testing, field uniformity is one of the most critical factors. A non-uniform field leads to inconsistent exposure of the equipment under test (EUT), making results dependent on its exact placement. This can compromise both repeatability within one laboratory and reproducibility between different test facilities.
Low frequencies antennas used for radiated immunity testing in the frequency range 10kHz – 30MHz have a poor radiating pattern uniformity, what negatively impacts the repeatability and reproducibility of the EMC immunity tests.
Parallel plate antennas are engineered specifically to overcome this challenge by generating a homogeneous electromagnetic field within its test volume (e.g. electric field of > 200V/m in the frequency range 10kHz to 30mHz).
The principle behind field homogeneity
The antenna consists of two parallel conductive plates fed by a symmetrical transmission line. The geometry ensures that the current distribution along the plates is stable and balanced. In this configuration:
- The electric field (E) is primarily uniform between the plates.
- The corresponding magnetic field (H) is perpendicular to the plates and equally distributed.
- Since the line is electrically symmetrical, reflections and standing waves are minimized, avoiding field distortions.
This design guarantees that the EUT experiences nearly identical field intensity and orientation throughout the usable test volume.
Easy polarization change
A unique advantage of Montena’s parallel plate antenna is the ability to switch polarization simply by rotating the structure, while the EUT remains in the center of the test zone. This eliminates the need to move or reposition the EUT, saving time and ensuring consistent test conditions. This feature is especially valuable when both vertical and horizontal polarizations are required by EMC standards.
Technical advantages
- Consistent Exposure: Equipment can be positioned anywhere within the test area and will still be subjected to the same field conditions.
- Fast Polarization Switching: Rotate the plates to change polarization—no need to touch the EUT.
- Compliance with Standards: Homogeneity and polarization flexibility support tests in accordance with ISO 11451-2, EN 55035, and MIL-STD methods (MIL-STD-461 RS103).
- Reproducibility Across Labs: The stable geometry ensures that tests carried out in different facilities deliver comparable results.
Practical design considerations
Montena’s parallel plate line can be installed in an anechoic chamber or open area test site. Its modular structure allows for quick dismounting, ensuring flexibility when the space is needed for other measurements. To preserve homogeneity, care must be taken to minimize nearby metallic structures that could induce resonances and disturb the field distribution.
The homogeneous electromagnetic field and the easy polarization switching of Montena’s parallel plate antenna provide engineers with a powerful and efficient tool for EMC immunity testing. By combining optimized geometry, symmetrical design, and practical usability, this antenna ensures reliable, repeatable, and standard-compliant results—all while simplifying the testing process.
