Microstrip-slot transitions and its applications in multilayer microwave circuits

Abstract

The rapid development of wireless communication systems has put a lot of demand for compact RF fronts. Nowadays, these subsystems mostly operate in microwave frequency bands and include amplifiers, filters and mixers, which are accompanied by lumped capacitors, inductors, resistors and distributed circuits in the form of sections of transmission lines. With regard to the choice of technology, planar technology including microstrip, stripline, slotline or coplanar waveguide is preferred for an RF front end design because of low manufacturing cost. The demand on minimizing the occupied area by RF front end requires utilization of two sides of substrates on which passive and active devices are to be developed. A further demand on compactness calls for use of a multilayer planar approach. In such cases, the challenge is in passing a signal between two sides of a dielectric layer. A suitable transition (also named via) of wire or wireless type is required to accomplish this task. To couple DC signals wire-type transitions are unavoidable. However, when only a RF signal has to be passed, a wireless via can be a more convenient choice. The most common transition for coupling a RF signal between two sides of planar dielectric structure is the microstrip-to-slotline transition. Its convenience is that it achieves this function using wireless means, making the manufacturing process cost effective. It is important to understand the fundamental properties of this transition, as well as it is imperative to have its design guidelines. Also it is important to know its applications in basic microwave circuits and devices. This chapter provides an overview of design of a microstrip-slot transition, explains its operation and gives examples in which such transition can play a useful role.