Real Frequency Technique for Broadband Power Amplifier Design
High Power Broadband Power Amplifiers are the vital building blocks of many wireless communications systems (Base stations-LTE: $500 Billion by 2017, Connected devices: More than 50 Billion units by 2017 with several hundreds of Billions dollars of systems), New Generation Base Stations (Trillions of dollars of emerging market by 2020), Many kinds of Radars for various applications (Land Radars, Mobile radars, Smart Cars, surveillance, Trillions of dollars of emerging market by 2025) etc.
Emerging global wireless market directs us to work with GaN HEMT devices to design broadband high power amplifiers starting from several hundreds of MHz to X-Band.
GaN power transistors shows weird input and output load-pulled measured input and output impedances. Especially, as the operating frequency increases, real parts of the impedances drastically drops from several tenth ohms down to fractions of ohms. That is to say away from 50 ohms (1 to 100).
Therefore, design of Input and output matching networks (IMN & OMN) becomes highly crucial. Element values of IMN and OMN shows wide spread which may be difficult to manufacture if not impossible.
In this case, design philosophy and methods of matching networks become very important to end up with reasonable gain, high Power Added Efficiency over wide frequency band of operations.
One have the following options to design IMN and OMN
• Design with Lumped Elements
• Design with transmission lines (distributed elements) such as microstrips
• Design with mixed lumped and distributed elements (in short, with mixed elements).
In this work, several “actual - high power - broadband RF and microwave amplifier” design examples are presented using lumped, distributed and mixed elements. In the course of designs, “Real Frequency Synthesis Robot” is employed2. Furthermore, it is shown that, X-Band- broadband PA designs are not technically-feasible with distributed elements. However, they can be manufactured using lumped elements employing MMIC technology. On the other hand, if one prefers to employ discrete components, then mixed element design is inevitable, technically feasible and economically cheap.