Packaged microwave integrated circuits

Because of the increasing operating frequency and complexity of the circuits, the prediction of the package behavior and of the interaction between the package and the enclosed circuit itself is becoming more and more significant. In most of the commercial microwave simulators, the presence of the package is taken into account by simply considering the reactance introduced by the electric walls close to the circuit; unfortunately, when the package supports resonant modes and when electromagnetic couplings between different parts of the circuit are present, this approach is not valid anymore. To overcome this limitation the full-wave FDTD simulator has successfully been used to investigate packaged MMIC circuits. In particular, the behaviour of packaged single and coupled MMIC via-hole grounds have been investigated; the theoretical analysis has been compared with experimental results showing excellent agreement. Moreover, since the package introduces resonances, we have investigated several different possibilities to choke off these resonances. It is shown that the common practice of inserting a damping layer just below the lid is often not effective. In particular, the importance of placing damping layers also on the side walls is demonstrated.

MMIC commercial package:

The behaviour of a commercial MMIC package operating in the range 0-40 GHz has been investigated. It consists of a mechanical support of kovar with a fused quartz substrate above it. The area where the MMIC must be placed is enclosed between glass side walls and a top metallic lid. The latter is connected to a ground plane by via-holes through the glass walls. Bias lines and metal backed CPW terminations are also present. It is interesting to note that this package is substantially an open structure. Within the operating frequency range, the electromagnetic shielding is realized by metallic via-holes connecting the lid with the ground plane. In order to compare theoretical and experimental results, a simple microstrip transmission line, inserted between the input and output ports has been simulated.