An amplifier is generally considered to be any type of device which uses a small amount of energy to control a larger amount of energy. However, the term today generally refers to an electronic amplifier. The relationship of the input to the output of an amplifier, which is typically expressed as a function of the input frequency, is known as the transfer function of the amplifier, and the magnitude of the transfer function is known as the gain.
Radio frequency amplifiers are electronic devices that can change the amplitude of a signal. These amplifiers are designed to produce a brand new output signal based on the input. The signal can be voltage, current or any type of signal however usually the input and output signals are of the same type, but separate circuits are used in the amplifier for the input and output signals.
The input circuit provides various degrees of resistance to an output circuit generated by the power supply. This process smoothes the current to produce an even, uninterrupted signal. To get a smooth output signal, a varying resistance is applied to the output circuit. Pre RF amplifiers are used to boost the output signal. The RF amplifier in turn, amplifies the signal.
There are various types of RF amplifiers such as: limiting amplifiers, bi-directional, low noise, multi-carrier, buffers and pulse. Other types of RF amplifiers that offer broadband amplification are DLVA (Detector log video amplifiers), SDVLA (Successive detection log video amplifiers) and ERDVLA (extended range detector log video amplifiers).
Some electrical factors that you should consider while selecting a RF amplifier include: the operating frequency, the frequency range of the RF amplifier, the gain, the ratio of output to the input power, the output power, the gain flatness, the nominal operating voltage, the impedance, the operating temperature and the noise figure.
The physical factors you should consider include the package type and the connector type. Package types include the SMT (surface mounts), flat pack and through hole. Connector types include BNC, MCX, mini UHF, MMCX, SMA, SMB, SMP, TNC, type F, type N, UHF, 1.6 / 5.6, and 7/16.