This paper presents a measurement fixture suitable for measuring substrate carried noise for lightly doped substrates within the UWB frequency band. Signals coupling through the substrate are usually fairly weak and special precautions are taken to avoid any distortions that may be caused by the test fixture. The proposed measurement fixture is based on a modified ground-signal-ground (GSG) pad fixture. Parasitic effects in the measurement fixture are evaluated with help of an equivalent circuit model. From measured results, the presented fixture is shown to provide a measurement band from 3 to 10 GHz. As an example of the usability of the presented fixture a test-case using a class-E PA is presented. The noise injected by the class-E PA is measured using the proposed fixture as noise detector and the results are show to be accurate to within ±1.5 dB.
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