5.14: Summary

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This chapter introduced the richness of microwave components available to the RF designer. Microwave lumped-element \(R,\: L,\) and \(C\) components are carefully constructed so that they function as intended up to \(20\text{ GHz}\) or so. They are usually in surface-mount form so that they can be integrated in design without the parasitic effects of leads. To a limited extent, transmission line discontinuities can be used as small-valued lumped elements. Even if the transmission line discontinuities are not specifically introduced for this purpose, their lumped-element equivalent circuits must be included in circuit analysis. Transmission line stubs are widely used to introduce capacitance and inductance in circuits. In most transmission line technologies only shunt stubs are available, and thus there is a strong preference for shunt elements in circuit designs. Many functionalities can be developed using the interactions of forward- and backward-traveling waves on transmission lines. Classic examples seen in this chapter are the combiners and hybrids. Sometimes the functionality can only be visualized using transmission line structures. Then coming full circle, lumped-element equivalents can be realized.

There are many more passive components in the repertoire of the RF designer. However, this chapter reviewed the most important and introduced the concepts that can be used to analyze other structures and to invent new ones. Each year new variants of microwave elements are developed and documented in patents and publications. Microwave engineers monitor these developments, especially in their field of expertise.