Choosing Circuit Materials for Low-PIM PCB Antennas

Compact planar PCB antennas are also of growing interest at millimeter-wave frequencies, such as for 77-GHz Advanced Driver Assistant Systems (ADAS) for automotive electronic safety systems, for such functions as blind-spot detection, automatic braking systems, and collision avoidance. Because signal power levels are low in such systems, ADAS receivers rely on high sensitivity to reliably detect radar returns reflected from targets such as pedestrians and other vehicles. [...]in general, circuit materials for radiating antenna elements such as microstrip patches should be relatively thick and with low Dk value (2.2 to 3.5, for example). [...]order products are problematic because they can fall within the receiver’s frequency band and can block reception if at suitably high levels. [...]fifth-, seventh-, and ninth-order PIM products are usually at power levels that do not affect receiver performance.