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In this paper, a one-port test approach is proposed for testing radio frequency (RF) interconnects as well as RF passive filters embedded in RF substrates. The proposed technique relies on the use of an RF oscillator that is coupled to the embedded interconnect/filter via a probe card. Shifts in the RF oscillation frequency (referred to as resonance-based test) are used for defect detection, and are different from prior oscillation-based test techniques that configure the device under test itself into an oscillator. A core innovation is that the technique can detect defects in embedded passives/filters using only one-port probe access and eliminates the need of an external RF input test stimulus. Such one-port probing causes a shift in the oscillation frequency of the external oscillator because of the loading from the embedded RF passive circuit. To facilitate test response measurement, the output of the external RF oscillator (GHz signal) is down-converted to lower frequencies (MHz). The proposed test method is demonstrated through both simulations and measurements. Additionally, panel-level testing of RF substrates is illustrated.