Over-the-Air Measurement for Imaging Radar

The automotive industry is witnessing significant advancements in radar technology, particularly in advanced driver-assistance systems (ADAS) and autonomous vehicle applications. As radar systems become integral to ensuring safety and enabling smart transportation, accurate and reliable performance evaluation becomes critical. Conventional automotive radar sensors suffer from low resolution, prompting the rise of imaging radar as a promising solution. The emergence of imaging radar with improved resolution makes a significant improvement in the automotive industry, enhancing perception capabilities and paving the way for ADAS and autonomous driving technology.

Imaging radar offers significant advantages over conventional radar, especially in providing elevation information. The term "imaging radar" comes from its capability to deliver high-resolution point cloud outputs, enabling more detailed environment mapping. These radars must undergo stringent testing before they are deployed in the vehicles since their sensor capabilities affect the performance of ADAS features.

Engineers typically use over-the-air (OTA) measurements to test the functionality of the radar module. Depending on the parameters to be measured, these are the three main types of tests transmitter test, receiver test, and functional test. 

Transmitter testing includes power measurements such as effective isotropic radiated power (EIRP) or occupied bandwidth (OBW), and signal quality measurements such as modulation type, chirp duration, linearity, and frequency slope. Signal analyzers or oscilloscopes are commonly used for these tests. The receiver test assesses sensitivity and saturation levels, and resilience to external interference using signal generators or arbitrary waveform generators (AWG) as the signal sources. 

Functional testing validates the radar module target detection capabilities including accuracy, dynamic range, and resolution in detecting distance, radar cross section (RCS), speed, and angular position (in both azimuth and elevation). These parameters can be tested using equipment like radar target simulators (RTS), which simulate various target characteristics.

To ensure a controlled and traceable environment with minimum reflections and external interference, it's recommended that these automotive radar OTA measurements are performed in an anechoic chamber. 

There are two common OTA methods for automotive radar testing: direct far-field testing and indirect far-field testing using a compact antenna test range (CATR) chamber. 

The relationship between antenna size and far-field distance is essential in OTA testing, as an increase in antenna size directly leads to an increase in the far-field distance. Understanding this correlation is crucial in determining the appropriate testing environment.

Larger antenna sizes present challenges during over-the-air (OTA) measurements. This application note discusses and illustrates the setups for both direct far-field testing and indirect far-field testing using a CATR chamber. It also demonstrates the benefits of using a CATR chamber to accurately characterize over-the-air measurements for the larger automotive imaging radars using a comparatively smaller test footprint.