The influence of materials properties on the performance of microwave planar components

There is considerable industrial interest in the use of ceramic interconnect technologies to meet the requirements of microwave circuits for commercial communication systems currently operating in the low microwave region. Whilst there is an increasing volume of literature on the performance of these materials, and the methods used to characterize them, little has been published on the direct effects that material properties will have on the microwave performance of typical circuits. In this paper we address this issue by considering how two of the principal performance indicators, namely loss tangent and dielectric constant, affect the high frequency behaviour of microwave receivers. LTCC fabrication technology is particularly attractive for applications in the 1-5GHz, including mobile handsets and Bluetooth modules and we use the results of published data to see how the behaviour of commercially available materials affects high-frequency circuit performance. One of the principal effects considered in this paper is that of noise. We see how increases in interconnection and circuit losses have a direct effect on receiver noise performance. Packaging is becoming an increasingly more important issue at microwave frequencies, particularly with driving forces in the mobile handset market continually requiring greater functionality, which often means more circuitry, in ever smaller spaces. Thus component size and the ability to place components in close proximity is one of the key issues facing the circuit designer. The dielectric constant of the substrates used is of prime importance here and by using practical, published data we examine how the various interconnection technologies will affect, and limit, the component packing density.