Resonance phenomena on Yagi arrays

The Yagi antenna has been studied experimentally and theoretically and a class of resonance phenomena has been found to occur in a narrow frequency range immediately below the director array cutoff frequency. This resonant behaviour is characterized in the swept-frequency far-field graphs by a very narrowband reduction in gain and in the input impedance by very rapid fluctuations with frequency. The dispersion characteristics of arrays of dipole elements are used to suggest a design procedure which prevents the occurrence of such resonances.