When substrates are mounted with tape; a cavity is created under the substrate. The cavity may have potential resonating frequencies within the frequency band of interest. If a bond wire transition between different substrates is used; the cavity resonance may lead to undesirable reflections. The problem can be addressed in different ways. Two methods will be briefly discussed in this paper: coplanar wave-guide-transitions and a ‚Äúphase-cancelling‚ÄĚ technique. Results from simulations and prototype card measurements are presented. The primary frequency range is the X-band (8-12 GHz).