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RF and Microwave Transmitter Design by Andrei Grebennikov

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3

IMPEDANCE MATCHING

This chapter begins by describing the main principles and impedance matching tools. Generally, an optimum solution depends on the circuit requirement, such as the simplicity in practical realization, the frequency bandwidth and minimum power ripple, design implementation and adjustability, stable operation conditions, and sufficient harmonic suppression. As a result, many types of the matching networks are available, including lumped elements and transmission lines. To simplify and visualize the matching design procedure, an analytical approach, which allows calculation of the parameters of the matching circuits using simple equations, and Smith chart traces are discussed. In addition, several examples of the narrowband and broadband power amplifiers using bipolar or MOSFET devices are given, including successive and detailed design considerations and explanations.

3.1 MAIN PRINCIPLES

Impedance matching is necessary to provide maximum delivery to the load of the RF power available from the source. This means that, when the electrical signal propagates in the circuit, a portion of this signal will be reflected at the interface between the sections with different impedances. Therefore, it is necessary to establish the conditions that allow to fully transmit the entire electrical signal without any reflection. To determine an optimum value of the load impedance ZL, at which the power delivered to the load is maximal, consider the equivalent circuit shown in ...

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