Theory and Proposed Method for Determining Large Signal Return Loss or "Hot S22" for Power Amplifiers Using Phase Information

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  • Author: Patrick Naraine and Chandra Mohan
Power amplifiers (PAs) are a critical functional block in today’s wireless communications. They are found in every cell phone, cordless phone, RF remote controller, etc. Any application requiring the wireless transmission of analog or digital signals will require a PA. The PAs are usually placed as close as possible to the antenna in wireless equipment to minimize RF losses, maximize power efficiency and maximize battery life. RF systems engineers need to determine the PA return loss under actual output power drive levels. This so-called “Hot S22” is needed to calculate mismatch loss at the antennae interface, and to determine the actual wireless system transmit power (a key requirement for regulatory bodies, e.g. FCC).