Frequency agile antenna tuning and matching

Automatic antenna tuners (AATU) have for some time been an essential component of most HF communications systems; however, the changing operating modes used at HF call for continual development and improvement of AATU equipment, especially in terms of tuning speed. Matching network design involves complex trade-offs between impedance matching range, losses and practical realisation of components. Currently, most AATU designs use binary switched arrays of components to implement variable components, relays being the switching devices of choice. Future developments may see greater use of semiconductor switches. Desirable features of impedance sensors are the ability to provide impedance phase and magnitude data, with low radiated power, and maximum immunity to external signals. Tuning algorithm design aims to minimise the duration of the tuning cycle, whilst being able to accommodate wide variations in impedance levels