The millimeter Wave (mmW) radar characterization, testing, verification challenges and opportunities

Abstract

The modern millimeter wave (mmW) Radar exhibits distinct advantages over lower band (L, C, X, Ku, K, Ka) radars providing lower radar cross-section (greater stealthiness), multimode multi-target acquisition/tracking capabilities, long target-detection range, enhanced spatial resolution, agile maneuverability, superior survivability, all weather capabilities and greater reliability including reduced SWaPC metric. The mmW Radars are also at the forefront of the Advanced Driver Assistance Systems (ADAS), which are making their way into many of the high end automobiles at present. Adaptive cruise control, automatic braking, backup object detection, blind-spot detection, cross-traffic alerts, and lane-change assist take advantage of many mmW radar capabilities. The goal of ADAS is to reduce driver error and, therefore, decrease the number of crashes, injuries, and fatalities. In fact, these systems have been so effective that the government is contemplating ADAS for most of the future cars. The mmW Radar also lends handsomely towards the compact and low cost design of phased array antennas capable of beamforming and beam steering (dynamically pointing them in the desired direction). They enable beam steering without any moving part and an antenna beam is formed by an array of smaller antenna elements, such as individual patches or dipoles. By varying the relative phases and amplitudes of the signals applied to the individual receiver/exciter elements, the antenna array can shape and steer a beam in the desired direction. The compactness and low profile design of mmW phased array system presents daunting challenges to test and verification engineers since many of these intermediary points are neither accessible nor adequate to calibrate and/or characterize the system performance (e.g. uniformity, linearity, coverage, sensitivity etc…). To overcome these challenges, two approaches are employed to characterize such a compact and complex system – far-field and near-field mode, each with their own advantages and disadvantages. The far-field mode characterization can be done either outdoor or indoor but requires large anechoic chamber, sensitive and highly uniform and calibrated probe element as well specialized test equipment for injecting, collecting and analyzing the signals. The near-field mode testing has some unique advantages, where testing can be performed in a close range requiring far less complex anechoic chamber, simple test probe, easy test setup and majority of the characterization and error corrections can be done off-line utilizing sophisticated signal processing techniques. This paper analyzes the far-field and near-field testing methods of the mmW Radar systems and delineates the challenges and opportunities in enabling a low cost solution to the military and automotive world.