Why are cavity modes a problem?
Cavity modes are excited with RF power that would otherwise be used to perform a useful function. These parasitic modes show up in RF system measurements as undesired nulls in insertion loss, and as undesired peaks in return loss. Phase response may also vary unpredictably at frequencies near a cavity resonance. • Q: Why is an EBG structure useful inside an RF package? A: At frequencies above 10 GHz, EBG structures are small enough to be fabricated into the cover and/or base of a shielded RF package. EBG structures can be designed to cutoff parallel-plate waveguide (PPW) modes. When PPW modes reflect off the walls of a shielded package, they resonate to become cavity modes. When PPW modes are excited by a given signal interconnect or transmission line, and couple into a nearby interconnect or transmission line, that is undesired crosstalk. EBG structures can suppress the propagation of PPW modes over a limited band of frequencies thus improving RF system performance by suppressing cros
