When it comes to automotive radar sensors, calibration is key. After all, mechanical misalignment of the radar sensor to the car body by only a few degrees will seriously degrade performance. Currently, radar calibration is typically achieved by mechanically aligning the radar sensor casing to the vehicle’s thrust vector. A laser-based optical system is used to measure the misalignment angle. As an alternative approach, a calibration system based on the measurement of electromagnetic (EM) waves has been presented by Benjamin Laemmle, Gabor Vinci, Robert Weigel, and Alexander Koelpin from Germany’s University of Erlangen-Nuremberg together with Linus Maurer from Austria’s DICE GmbH.

With their approach, the calibration also can handle the misalignment of the radar board to the casing. Beyond automotive radar calibration, their six-port receiver front end can perform the angle-of-arrival (AOA) detection of 77-GHz signals for direction finding (DF) or high-precision industrial radar systems. The millimeter-wave integrated circuit (IC) leverages a measurement principle rooted in the passive superposition of two incident signals and power detection. Essentially, the magnitude of the four phase-shifted, superposed signals is downconverted to baseband by power detection. The phase difference—and thus the AOA of the two input signals—can be calculated from the four output voltages.

Included in this IC are the following: two input amplifiers; a broadband, passive six-port network; and four power detectors. The IC operates across a 3-dB bandwidth from 75 to 84 GHz. At 80 GHz, it boasts responsivity of 152 kV/W. The IC consumes 95 mW from a 5-V supply. It measures just 1028 x 1128 μm2, having been fabricated in a 200-GHz fT silicon-germanium (SiGe) bipolar process. See “A 77-GHz SiGe Integrated Six-Port Receiver Front-End for Angle-of-Arrival Detection,” IEEE Journal Of Solid-State Circuits, Sept. 2012, p. 1966.