Radio Frequency Amplifier

An RF power amplifier is a type of electronic amplifier used to convert a low-power radio-frequency signal into a larger signal of significant power, typically for driving the antenna of a transmitter. It is usually optimized to have high efficiency, high output Power(P1dB) compression, good return loss on the input and output, good gain, and optimum heat dissipation.

The basic applications of the RF amplifiers include driving to another high power source, driving a transmitting antenna, microwave heating, and exciting resonant cavity structures. 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). Microwave or RF heating is an industrial application which is also benefiting our homes in the form of microwave ovens. Exciting cavity resonators is quite a research lab and industrial application of an RF source. Particle accelerators utilize RF sources extensively.

Amplifiers are available in a large number of form factors ranging from miniscule ICs to the largest high-power transmitter amplifiers. In the following discussion the focus will be on solid state power amplifiers used at microwave frequencies, particularly in test and measurement applications.

Microwave power amplifiers may be used for applications ranging from testing passive elements, such as antennas, to active devices such as limiter diodes or MMIC based power amplifiers.

Furthermore, other applications include testing requirements where a relatively large amount of RF power is necessary for overcoming system losses to a radiating element, such as may be found at a compact range, or where there is a system requirement to radiate a device-under-test (DUT) with an intense electromagnetic field, as may be found in EMI/EMC applications.

As varied as the system requirements may be, the specific requirements of a given amplifier can also vary considerably. Nevertheless, there are common requirements for nearly all amplifiers, including frequency range, gain/gain flatness, power output, linearity, noise figure/noise power, matching, and stability. Often there are design trade-offs required to optimize any one parameter over another, and performance compromises are usually necessary for an amplifier that may be used in a general purpose testing application.

In other words a radio frequency amplifier is a tuned amplifier that amplifies the high-frequency signals commonly used in radio communications. The frequency at which maximum gain occurs in a radio-frequency (rf) amplifier is made variable by changing either the capacitance or the inductance of the tuned circuit. A typical application is the amplification of the signal received from an antenna before it is mixed with a local oscillator signal in the first detector of a radio receiver. The amplifier that follows the first detector is a special type of rf amplifier known as an intermediate-frequency (i-f) amplifier. See also Amplifier; Intermediate-frequency amplifier.

An rf amplifier is distinguished by its ability to tune over the desired range of input frequencies. The shunt capacitance, which adversely affects the gain of a resistance-capacitance coupled amplifier, becomes a part of the tuning capacitance in the rf amplifier, thus permitting high gain at radio frequencies. The power gain of an rf amplifier is always limited at high radio frequencies, however.