Floating Circuit S-parameter Measurement Using Indirect Measurement Method

Many devices mounted on automobiles have a certain distance from the metal body that can be seen as a ground plane. As a result, they should be treated to have floating PCB configurations in high frequencies. In this paper, a novel measurement method to obtain a measurement-based model for a four-port floating PCB as a DUT is proposed. A pair of fixtures are used, each of which consists of a small PCB and short wires to a DUT. The PCB has a pair of microstrip-line patterns and is arranged vertically on a reference ground plane so that it can be fed beneath the ground plane. The characteristics of the fixture, including the coupling to the DUT, are measured by applying our previously proposed ‘indirect measurement’ method. They are de-embedded after measuring the DUT using the fixtures.To show the potential of this method, we compare the results of estimation and measurement for a body-only test vehicle system up to 700MHz. A pseudo-ECU PCB is mounted as a DUT floating in 5cm above an extended body ground with a noise source, and the noise propagation is measured with a testing antenna placed in front of the vehicle.