Analysis and design of compact third-order intermodulation generation circuits

In this article, we analyzed and designed miniaturized third-order intermodulation distortion (IM3) generation circuits. An antiparallel Schottky diode pair was adopted for nonlinearity generation. A reflective configuration using a 90° hybrid coupler was employed to acquire a pure IM3 signal at the output. The fundamental signal at the output was automatically suppressed below the IM3 level using a reflective load optimized for the fundamental impedance of the antiparallel diode pair. The IM3 generation characteristics were fully analyzed using the Volterra series under a weak nonlinear assumption. A new optimum matching condition of the reflective load for the perfect fundamental cancellation was derived. A miniaturized 12 × 14 mm² IM3 generator was designed and implemented for the 2.16 GHz band, based on the analysis results. The output performance measured for the implemented IM3 generator matched the calculated results. The IM3 generator showed excellent fundamental cancellation characteristics and had a wide operational range for the input signal level.