On the Null Frequency Scanning Antenna: History, Theory and Recent Progress

A mini-survey for null frequency scanning antennas (NFSAs) is presented in this article. NFSAs based upon different operation principles are classified and reviewed at first. Then, this article concentrates on the recent advances of multi-mode resonant null frequency scanning antennas (NFSAs). Mode synthesis design approach to NFSAs is introduced. Finally, possible developing trends of multi-mode resonant NFSAs are prospected.