RFEMI Antennas: Biconical, Broadband, and Log Periodic
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EMI antennas, including biconical, broadband, and log periodic types, are essential tools for detecting and measuring electromagnetic interference (EMI). This article details these three popular antenna types, highlighting their roles in EMI/EMC testing.
As we know, EMI is the short form of Electro-Magnetic Interference. EMI testing involves both interference and susceptibility tests.
- Interference tests involve evaluating the impact of a system under development on nearby wireless systems when the system is powered on. The system under development should not radiate unwanted EM waves. To mitigate such leakages, EMI filters and proper shielding materials are used during design and manufacturing.
- Susceptibility (or Immunity) tests assess the robustness of a system under development against EM radiation from nearby wireless systems, such as cellular towers, base stations, or wireless access points.
The following EMI antennas are used for these tests, specifically for commercial radiated emission measurements. Refer to EMI and EMC vendors for more information on related products and services.
Biconical Antenna
A biconical antenna consists of two conical conductive elements arranged symmetrically around a central feed point. It operates over a relatively wide frequency range, typically 30 MHz to 300 MHz.
Features:
- Wideband Operation: Offers consistent performance over a broad frequency range.
- Omnidirectional in the Horizontal Plane: Captures signals equally in all directions horizontally.
- Linear Polarization: Useful for measuring horizontally or vertically polarized emissions.
Applications:
- Used in EMI testing for low to medium frequency ranges.
- Ideal for measuring radiated emissions in compliance testing.
Figure 1: Biconical Antenna
Broadband Antenna
A broadband antenna refers to antennas capable of covering a very large frequency spectrum. Examples include log periodic antennas, biconical antennas, and hybrids of different designs.
Figure 2: Broadband Antenna type
Features:
- Large Frequency Range: Depending on the design, broadband antennas can operate from 30 MHz to several GHz.
- Compact and Lightweight: Modern designs are optimized for portability.
- Wide Applications: Can be used for both transmitting and receiving purposes.
Applications:
- Used in EMI/EMC testing for higher frequency ranges.
- Common in applications where wideband frequency coverage is required, such as testing wireless communication devices.
Log Periodic Antenna
A log-periodic antenna is a type of directional broadband antenna with elements arranged in a logarithmic scale. Its structure ensures consistent impedance and gain over a wide range of frequencies.
Figure 3: Log Periodic Antenna
Features:
- Frequency Range: Typically operates from 80 MHz to several GHz.
- Directional Pattern: Provides high directivity for targeted measurements.
- Consistent Impedance: Ensures minimal reflections across its operating range.
Applications:
- Frequently used in EMI/EMC testing for high-frequency emissions.
- Ideal for testing communication devices and systems that require directional measurements.
Conclusion
Choosing the right EMI antenna ensures accurate interference detection and compliance testing. Understanding their designs and applications enhances testing efficiency.
