Multi-layer thick-film microwave components and measurements

The trend in wireless and mobile communications for broader bandwidth microwave circuitry, coupled with high packaging density and low cost fabrication has triggered investigations of new circuit configurations and technologies that meet these requirements. We have addressed these issues through the study of multilayer microwave structures using advanced thick-film technology. The techniques described employ several layers of metal sandwiched by thick-film dielectric. This leads to an efficient solution for system miniaturization. Characterization of 2-layer thick-film microstrip line has been carried out through electromagnetic computation and practical measurement, and this has established the basic database for designing multilayer thick-film microwave structures. It is also shown that the use of multilayer thick-film microstrip permits the realization of very high characteristic impedance lines on high dielectric constant substrates, without the need for very narrow lines. The high impedance capability of this structure is very attractive for the implementation of low-loss matching networks and passive components with enhanced bandwidth performance. Strong coupling, that is often required in the design of microwave couplers and filters, is difficult to realize in conventional single layer structures, due to the requirements for very narrow gaps. However, by using multilayer structure, strong coupling can be easily obtained by overlapping conductor tracks in different layers, with less stringent geometrical requirements. A multilayer end-coupled microwave filter centered at 10GHz using thick-film technology has been designed and simulated. A 30% bandwidth has been achieved which shows a very significant improvement over conventional single layer structures, where the bandwidth achievable is normally less than 5%. The significance of this work is that it shows that the multilayer approach to microwave structures, coupled with new thick-film technology, offers a viable and economic solution to achieving high-density, high-performance microwave circuits.