What Is a Microwave Amplifier?

A microwave transistor amplifier (microwave transistor ampli & shy; fier) uses a transistor as an active device to amplify a microwave signal. Divided into microwave high power amplifier, microwave low noise amplifier.

A microwave transistor amplifier (microwave transistor ampli & shy; fier) uses a transistor as an active device to amplify a microwave signal. Divided into microwave high power amplifier, microwave low noise amplifier.

Microwave transistor amplifier

Microwave power amplifiers are used to amplify stronger microwave signals. The main indicators are: output power, nonlinear distortion. Non-linear distortion will cause distortion of amplitude modulation signals, such as AM, MQAM, etc., and broaden the spectrum of the band-limited signal. Measures to reduce non-linear distortion generally include power back-off method and pre-distortion method. The power back-off method is to reduce the output power so that the transistor operates in the linear region. It is to add appropriate distortion components to the input signal to make it cancel out the newly generated distortion in the amplifier. After taking these measures, nonlinear distortion can generally meet the requirements.

When the output power of a microwave transistor is limited, and a larger power output is required, a power synthesis technology (see power amplifier) is used. The principle is shown in Figure (a). The power combiner shown in Figure (b) can be used, and other coupling structures can also be used. When a power combiner is used, it is required that the signal amplitude and phase of a pair of input terminals must be the same, otherwise the power cannot be completely added and power is lost.

figure 1

The structure of the microwave power amplifier is generally a microstrip structure. The scattering parameters and related characteristic parameters are assisted by the computer system.

The development of microwave transistor amplifiers is rapid. The advent of microwave metal-semiconductor field-effect transistors and MESFETs has enabled the operating frequency band to be extended from 1GHz to 30GHz, and the linear output power is greater than several tens of watts. Performance.

Microwave transistor amplifier

The microwave low noise amplifier device at the input end of the microwave receiver amplifies the noise level of the receiver and directly determines the lowest signal level that the receiver can receive, so the low noise amplifier has an important role in improving the sensitivity of the receiver. The microwave low-noise amplifier is composed of a microwave low-noise transistor and a microstrip circuit, and is designed using scattering parameters. Microwave low-noise transistors have developed rapidly with advances in technology, structure, and materials.