RF power amplifier Radio

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A radio frequency power amplifier (RF power amplifier) is a type of electronic amplifier that converts a low-power radio-frequency signal into a higher power signal. Typically, RF power amplifiers drive the antenna of a transmitter. Design goals often include gain, power output, bandwidth, power efficiency, linearity (low signal compression at rated output), input and output impedance matching, and heat dissipation.

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Amplifier classes

Many modern RF amplifiers operate in different modes, called "classes", to help achieve different design goals. Some classes are class A, class B, class C and class E. There is a Class D, but those amplifiers can work only with low frequency signals typically used in audio equipment.

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Solid state vs. vacuum tube amplifiers

Modern RF power amplifiers use solid-state devices such as bipolar junction transistors and MOSFETs. Transistors and other modern solid-state devices have replaced vacuum tubes in most electronic devices, but tubes are still used in some high-power transmitters (see Valve RF amplifier). Although mechanically robust, transistors are electrically fragile - they are easilly damaged by excess voltage or current. Tubes are mechanically fragile, but electrically robust - they can handle remarkably high electrical overloads without appreciable damage.

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Applications

The basic applications of the RF power amplifier include driving to another high power source, driving a transmitting antenna and exciting microwave cavity resonators. Among these applications, driving transmitter antennas is most well known. The transmitter-receivers are used not only for voice and data communication but also for weather sensing (in the form of a radar).

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Wideband amplifier design

Impedance transformations over large bandwidth are difficult to realize, thus most wideband amplifiers use 50 ? output loading. Transistor output power is then limited to

${\displaystyle V_{br}}$ is defined as the breakdown voltage

${\displaystyle V_{k}}$ is defined as the knee voltage

and typically ${\displaystyle Z_{o}=50\Omega \,}$

The loadline method is often used in RF power amplifier design.

Source of the article : Wikipedia