Free Space Quasi Optical Transmission Loss Calibration for Radome Materials
Calibrate free-space quasi-optical benches with time-gated TRL standards to prevent radome transmission loss from breaching radar EIRP regulatory limits.
Radome Transmission Loss
Meaning
Power reduction metrics evaluate the proportion of electromagnetic energy absorbed or reflected by a protective antenna cover. Analyzing radome transmission loss tells engineers how much of the transmitted radar signal is lost when passing through the protective housing. This parameter is specified in decibels and directly affects the maximum detection range of the enclosed radar sensor.
Lower loss values are necessary to ensure the signal can reach distant targets and return with sufficient power.
Loss Mechanism
Dielectric absorption and surface reflections are the primary physical factors that reduce the power of a propagating wave. In radome transmission loss, the material’s loss tangent determines how much energy is converted into heat within the plastic wall. Surface reflections occur at the boundary between air and the radome material due to the mismatch in dielectric constant.
By matching the radome thickness to a multiple of a half-wavelength, these reflections can be canceled to minimize the total loss.
Sensor Performance
Reduced signal strength at the antenna terminals directly degrades the signal-to-noise ratio of the receiver. High radome transmission loss decreases the sensitivity of the sensor, which can lead to missed targets and slower response times in automated driving systems. This attenuation also increases the vulnerability of the system to external noise and interference.
Maintaining a low loss profile across the operational frequency band ensures that the radar maintains its high-resolution performance under all driving conditions.
Measurement Procedure
Laboratory testing on a specialized bench is required to verify that the manufactured housing meets the designed loss limits. Measuring radome transmission loss involves placing the empty radome between a transmit antenna and a receive antenna connected to a calibrated vector network analyzer. The technician measures the received power with the radome in place and compares it to a baseline measurement taken without the radome.
This test is repeated at different incidence angles to map the transmission characteristics across the entire surface of the protective cover. These measurements must be taken in an RF anechoic chamber to prevent reflections from nearby objects from corrupting the test data. The resulting data helps the integration team adjust the antenna’s positioning for optimal performance.