RF and Microwave Circuit Design

4Planar Circuit Design II: Refinements to Basic Designs

4.1 Introduction

At RF and microwave frequencies there are many circuit components and interconnections that exhibit significant non-ideal electrical performance. In particular, discontinuities in conducting tracks cause radiation and unwanted reactance. Similarly, the packaging of active and passive components usually introduces unwanted resistance and reactance at high frequencies. It is important for the circuit designer to appreciate how high-frequency effects may influence the performance of circuit designs, and how these designs may need to be refined in order to produce good performance. Whilst there is a wealth of CAD software, including electromagnetic simulation, now available to aid the high-frequency circuit designer, it is useful for the designer to be able to identify potential sources of non-ideal performance at the prototype design stage. Thus, the purpose of this chapter is to introduce some of the key areas where non-ideal performance occurs, and where possible quantify the effects through the use of worked examples.

Initially, the occurrence and RF consequences of some common microstrip discontinuities will be discussed, and information presented on typical compensation techniques. Since most practical RF circuits are encased in some form of protective package the effect of metallic enclosures on circuit performance will be discussed, and recommendations given on the optimum size of enclosure that ...