Modeling power amplifiers in the microwave office environment

Background and Objectives: A very difficult and urgent task is to obtain high output powers of transistor amplifiers. This class of devices in many radio engineering systems determines the most important technical parameters of the system, such as radiated and consumed power, bandwidth, dimensions and weight, reliability and cost. Known monolithic amplifier designs make it possible to obtain tens and hundreds of watts of output power. However, monolithic structures have limited operating frequency ranges, usually no more than a few hundred megahertz. Expansion of the operating frequency range of the power amplifier is possible by using discrete transistor crystals as active elements. The use of discrete crystals of transistors allows you to include elements of matching between amplification stages and significantly improve the main characteristics of the amplifier: VSWR of the input / output, gain, efficiency, operating frequency range (up to one octave or more). According to a number of criteria, a bipolar transistor of Russian production 2T937A was selected as active elements. Materials and Methods: When designing the amplifier, discrete crystals of a bipolar transistor 2Т937А were used. However, in computer modeling of radio engineering devices, it is necessary to take into account the absence of models of many Russian and foreign transistors in CAD libraries (in particular, Microwave Office), which significantly limits the possibilities of designing devices based on them. The article uses a computer model of the 2T937A transistor, obtained as a result of solving the problems of multicriteria optimization of the equivalent circuit of the transistor. Experimental characteristics of the bipolar transistor 2Т937А (static and frequency parameters) were used as optimization goals. The simulation of the transistor was carried out according to the equivalent Gummel – Poon circuit in the CAD Microwave Office. The article presents the design of a power amplifier based on 2T937A and its main units: power dividers / adders for two channels, a basic two-stage amplifier module. The corresponding problems of parametric and structural optimization are formulated and solved. Results: As a result of the research carried out, a microstrip power amplifier design was obtained on a 1 mm thick polycor substrate with a gain of 14–15 dB in the frequency range from 2 to 4 GHz. The output power is 22.5 W, the VSWR of the input and output is no more than 1.5. Conclusion: The device can be used as a pre-amplifier in the tasks of obtaining high values of the output power of the UHF and VHF ranges.