Antennas

An active antenna array of the kind comprising a plurality of switchable antenna elements controlled by a set of switches which is operable to selectively activate selected ones of the antenna elements to emit/receive a shaped beam of radiation, and wherein:

• the active antenna array is arranged to provide a first drive signal which causes the said set of switches to activate a first subset of said antenna elements at a first period of time, said first subset of antenna elements causing said antenna array to form a first beam having a first beam pattern, and to provide a second drive signal which causes said set of switches to activate a second subset of said antenna elements at a second period of time which is different from said first period of time, said second subset of antenna elements causing said antenna array to form a second beam having a second beam pattern, said first beam pattern and said second beam pattern comprising substantially identical far field radiation patterns but with different origins which are offset along an axis defined relative to said antenna array by a predetermined amount, and further comprising:
• a receiver which receives radiation that has been emitted by said antenna array and subsequently reflected from a target back to said antenna array when said antenna array is configured with the said first beam pattern and receives radiation that has been emitted by said antenna array and subsequently reflected from said target back to said antenna array when said antenna array has been configured with said second beam pattern,
• and further comprising a comparator which in use compares the said phase of the radiation received at said receiver when said antenna array is configured with said first beam pattern with the phase of said radiation received at said receiver when said antenna array is configured with said second beam pattern to provide a phase difference signal, and a target locator which determines the angular location of said target relative to said antenna array by processing said phase difference signal with said known offset between said different origins of said first far field radiation pattern and said second far field radiation pattern.