Loadbox Design for EMC Testing in Automotive GNSS/SDARS Application

In this work, a loadbox consisting of a distributed PCB diplexer was developed that is easy to fabricate with low cost, high durability and high reliability for EMC testing. The dual band diplexer was used to separate the combined signal coming from the LNA's output port to two separate GNSS and SDARS ports. At the GNSS and SDARS frequencies, due to the short wavelength of the RF signals, inductors and capacitors can be implemented using different transmission line geometries in short, open, parallel and straight-line formations. The distributed diplexer was designed using Keysight ADS RF Momentum software and fabricated on a 2-layer Isola FR402 PCB, with a thickness of 1.57 mm and a copper thickness of 17 um. The overall size was 5.8×3.1 cm. The return loss at the input port is better than 11.4 dB in both GNSS and SDARS bands. In the GNSS band, the measured isolation is better than 10.9 dB and the insertion loss is better than 1.9 dB. In the SDARS band, the measured isolation is better than 10.9 dB and the insertion loss is better than 2.1 dB. Simulated and measured S-parameters for all diplexer ports are in good agreement.