Considerations on measurement setup for second-order nonlinearity in radio-frequency bulk acoustic wave duplexers

This paper discusses influence of the setup on the measurement reliability and reproducibility for the second-order intermodulation distortion (IMD2) generated in the radio-frequency (RF) bulk acoustic wave (BAW) duplexers. Our measurements show that IMD2 level can be measured reliably and reproducibly given that the port termination is properly applied. For example, a filter and relatively large (>20 dB) attenuator (ATT) are necessary between an oscillator (OSC) and the antenna (ANT) port to suppress the non-linear mixing and the impedance mismatching. If order of these two devices is reversed, the IMD2 level changes significantly. Although an isolator is commonly used to stabilize the power amplifier (PA) output, from our results, it seems that isolator is not preferred. We also introduce the key know-how necessary for the reliable measurement, e.g., prior to the measurement, the PA output should be applied to the setup for the warm up; two OSCs and the spectrum analyzer should be synchronized to reduce frequency fluctuation.