Polymer Enclosure Attenuation Measurement under Millimeter Wave Radar Frequencies
Characterizing polymer permittivity and loss tangent under free-space conditions ensures radar enclosure attenuation remains within strict type-approval limits.
Radiated EIRP
Meaning
Total power emitted by an antenna in a specific direction relative to an isotropic radiator accounts for the combined effects of transmitter output and antenna gain. Radiated eirp is a fundamental metric used in the regulation and design of wireless systems to quantify the strength of the signal being transmitted. It provides a way to compare the performance of different transmitter and antenna combinations on a level playing field.
The value is calculated by adding the gain of the antenna in decibels to the power delivered to the antenna port in decibel milliwatts, while subtracting any losses in the cables or connectors. Regulatory bodies use this metric to set limits on the amount of interference a device can cause to other services. For engineers, it is a key parameter in determining the range and link budget of a communication or radar system.
Mathematical Formulation
The calculation of the radiated energy is a straightforward process that involves the addition of several independent factors. Radiated eirp is the product of the power at the input of the antenna and the antenna gain in the direction of interest. In logarithmic units, this becomes a simple addition of the transmitter power and the antenna gain, minus the insertion loss of the transmission line.
For example, a transmitter with an output of ten decibel milliwatts connected to an antenna with six decibels of gain and one decibel of cable loss will have a total of fifteen decibel milliwatts. This value represents the power that would need to be radiated by a theoretical isotropic antenna to produce the same signal strength in that direction. Understanding this relationship is necessary for optimizing the performance of the radio frequency front end.
Regulatory Compliance
Government agencies use this measurement to ensure that wireless devices do not exceed the allowable levels of electromagnetic radiation. Radiated eirp limits are set for different frequency bands and applications to prevent harmful interference between users of the spectrum. For automotive radar operating in the seventy-seven gigahertz band, the limits are designed to provide sufficient range for safety features while protecting other sensors.
Manufacturers must perform radiated measurements in a calibrated environment, such as an anechoic chamber, to prove that their devices comply with these rules. The resulting data is included in the certification report required for market access. Failure to meet these limits can result in the rejection of a product or the requirement for a significant redesign.
Measurement Verification
Determining the actual radiated power of a device requires a precise and controlled testing procedure. Radiated eirp is measured by placing the device under test on a rotating platform and measuring the signal strength at a fixed distance with a calibrated receiver antenna. The measurement is taken at multiple angles to find the peak power and the overall radiation pattern.
This process accounts for the real world performance of the antenna, including any effects from the device enclosure or nearby components. The results are compared to the theoretical calculations to verify the design and the quality of the manufacturing process. Regular testing during production ensures that the radiated power remains within the specified tolerances.
This verification is a critical part of the quality control process for high performance wireless equipment.