Automatic antenna-tuning unit for software-defined and cognitive radio

This paper discusses the implementation of an automatic antenna tuning unit system (ATU) for software-defined and cognitive radio. The ATU simplifies radio frequency (RF) front-end design for multi-band, multi-mode radios by allowing an electrically small reconfigurable antenna to become a frequency-agile selective component (essentially a tunable filter). In implementing the ATU, impedance synthesizers (tunable matching networks) using RF MEMS switches as the control elements are used to match a more or less arbitrary load to a convenient impedance value. To generate feedback data that can be used to optimize the impedance synthesizer, the incident and reflected powers at the input to the impedance synthesizer are sampled using a power sensor block comprising directional coupler, logarithmic RF power detectors, analog-to-digital converters (ADCS), and return loss computation algorithms running on a field programmable gate array (FPGA). From a practical point of view, in order to be compatible with commercial wireless handset devices, we propose to design and ultimately implement a fully integrated ATU system. In this paper, a hard- ware implementation of the ATU prototype has been demonstrated to verify narrowband automatic tuning ability of the ATU under constantly changing environment conditions, and we present simulated results for a logarithmic power detector designed with 55 dB dynamic range over the 800 MHz-2 GHz frequency band using 0.25 μ CMOS technology.