An EMI Test Bed for Automotive Active Antennas

Automotive antennas that require built-in RF amplifiers for services such as AM/FM, DAB, GNSS & Satellite Radio antennas are susceptible to Inter-Modulation, higher-order harmonic generation or high RF power compression or interference. These real-world scenarios are due to either mixing products of two or more signals or high RF power transmissions at some frequencies that occur only in specific geographical areas and are very hard to detect and quantify (such as multiple cell tower deployment by different cell network providers in the same location). This paper will present an EMI test bed that can reproduce such artifacts in a controlled manner using a shielded RF chamber with the ability to generate any combination of frequencies and power levels of any type for over-the-air signals to bombard fully assembled antennas and not just on a circuit board level as traditionally has been done in the past. This test bed is intended to help both antenna developers as well as Automotive OEMs discover and mitigate these issues at an early stage of the development with minimal costs. The test bed consists of a well-shielded EMI chamber with multiple signal generators, a spectrum analyzer, RF power amplifiers, audio harmonic distortion analyzer, high power RF switches and multiple transmit antennas inside the EMI chamber. The entire system is controlled by a self-developed software that can be automated to run multiple tests in sequence to examine the level of immunity of the Antenna Under Test (AUT) for any band of operation. Results for specific test cases will be presented such as cell Inter Modulation Rejection Ratio (IMRR) and compression for Satellite Radio, GNSS, AM/FM and DAB antennas.