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7.1: Introduction

  • Page ID
    41143
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    This chapter presents techniques for developing broadband matching networks. Sometimes these are akin to cascaded two-port matching networks. The general concept that works most of the time is to gradually step from an initial impedance to a final impedance. Design of broadband matching networks should also be done with the understanding that many RF systems will have multiple matching networks and so the maximum passband transmission loss of an individual matching network needs to be a fraction of a decibel so that when multiple networks are cascaded the insertion loss at the overall band edges will accumulate to equal the desired limit on loss. It is common to use a \(1\text{ dB}\) insertion loss threshold to define bandwidth so the individual matching networks may need to have a bandwidth defined by a loss that is much less with insertion loss thresholds as low as \(0.1\text{ dB}\) often used.

    Bandwidth is limited by energy storage and Section 7.2 introduces the FanoBode limits which are theoretical limits of what can be achieved in matching given reactive loads. It is not possible to exceed the Fano-Bode limits on bandwidth. Section 7.3 introduces the constant \(Q\) circles plotted on Smith charts to provide a visual guide for the design of broadband matching networks. The next three sections describe three types of broadband matching networks. The first, in Section 7.4, describes the stepped-impedance transmission line transformer which is a generalization of the quarter-wave transformer. Section 7.5 describes tapered transmission-line-transformers which are generalizations of stepped impedance broadband matching networks. An approach to broadband matching to reactive loads is described in Section 7.7.


    7.1: Introduction is shared under a CC BY-NC license and was authored, remixed, and/or curated by LibreTexts.

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