When engineers hear the term “radome,” they will usually visualize those large bubble-like domes protecting radar and data-link dish (or other) antennas from the elements. Despite their simple appearance, a conventional radome is a complex electronic and mechanical structure that must withstand wind, water, sun, and more, while its internal support elements must cause minimal disturbance to the antenna RF field. Furthermore, the enclosing material must be RF transparent at the frequencies in use.
But not all radomes are so obvious and visible. Today’s cars, with their use of 77- and 79-GHz bands (millimeter wave or mmWave) for radar and other advanced driver-assistance systems (ADAS) functions, also contain many smaller radomes used to conceal and protect the tiny antennas while also reducing drag. How can an automotive design know that the radome in use, such as a brand emblem or rear-view mirror housing, is actually transparent to RF at the designated frequencies?
1. The QAR System from Rohde & Schwarz allows for evaluation of automotive radome performance in the crucial 77- and 79-GHz bands.
The solution is to test these tiny radomes, and that’s where the QAR system from Rohde & Schwarz plays a role (Fig. 1). This imaging radome tester enables users to check, under automated control, various performance parameters such as RF transparency and homogeneity of these shell-like radomes.
These measurements indicate if sensor performance will be diminished or affected by the enclosure, and if other RF-based ADAS subsystems will work as planned with respect to factors such as sensitivity, range, intended coverage, and other parameters. Otherwise, reflections and attenuation in the radar sensor’s field of view will considerably impair sensor performance (Fig. 2). As explained in the reference provided below, even minute changes in thickness and other dimensions of the automotive radome can have a significant effect on its RF performance.
2. The influence of different radomes on radar cross section (RCS) and angle of incidence shows unsuitable radomes can cause angle errors.
Any defects in the77- and 79-GHz bands’ images of the QAR correspond directly to radar-signal impairments. The R&S QAR supports all material designs and form factors up to 30 × 50 cm, operates as an automated test center, supports full remote-control operation, and can be integrated into larger automated-test systems.
Rohde & Schwarz: Dr. Steffen Heuel; Tobias Köppel; Andreas Reil; Dr. Sherif Ahmed, “Enabling autonomous driving”