Measurement of spurious interference effects due to the excitation of low frequency leaky modes in a covered microstrip

This work studies the excitation of a physical leaky mode in a covered microstrip structure at low frequencies. A covered microstrip is a microstrip structure with a metallic top cover. This metallic top cover may be present in a microstrip structure due to a circuit package. Our previous numerical results have shown that for a sufficiently small top cover height a leaky mode can be excited on this structure at low frequencies. The interference between this leaky mode and the bound mode of the structure can cause spurious effects in the signal transmitted by the line. Thus, the objective of this work is to verify experimentally those numerical results. To do this we have designed and fabricated an experimental prototype of a covered microstrip line. For that structure our numerical analysis predicts an important destructive interference effect in the transmitted signal at a given (low) frequency. This will be verified by using a commercial electromagnetic simulator and by experimental measurements.