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Radio Frequency Power Amplifier

A radio frequency power amplifier (RFPA) is an electronic device designed to provide greater radio frequency (RF) power from its signal output port than the RF power supplied to its signal input port. RFPA's are used in many applications including cellular telephone systems, computer network systems, radio and television broadcasting, aviation, medical imaging and industrial applications. RFPAs use transistors or vacuum tubes to convert electrical energy supplied from a direct current voltage source into RF electrical energy. The first RFPAs were made in 19nn, for radio transmitters. An RFPA can be designed to be a linear amplifier, a non-linear amplifier, or provision can be made to allow operation as either.

Narrowband RF power amplifiers

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Wideband RF power amplifiers

An amplifier capable of passing a wide range of frequencies with a specified gain variation usually not more than 3dB along with specified signal integrity.

A wideband RF power amplifer provides uniform power amplification over much greater bandwidth than a tuned RF power amplifier. Most?? wideband RF power amplifiers provide non-reactive load impedance seen by the amplifying devices is resistive within the design bandwidth. Many wideband RF power amplifiers are designed to feed a $Z_{\text{L}}=50~\Omega$ output load. Power transistors usually develop their rated power output at load impedances, $Z_{\text{o}}$, of less than $50~\Omega$ . The required load impedance for a transistor or vacuum tube in class B or C can be estimated from:

$Z_{\text{o}}={\frac {(V_{\text{s}}-V_{\text{k}})^{2}}{2P_{\text{o}}}},$

where

$V_{\text{s}}$ is defined as the dc supply voltage,

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

$P_{\text{o}}$ is the output power.

Wideband transformers provide impedance transformation from $Z_{\text{o}}$ to the $50~\Omega$ output port of the amplifier.