Experimental study of novel resonant circular arrays

Recent studies have shown that large circular arrays of cylindrical dipoles possess very narrow resonances when the frequency is varied. Only one array element is driven, and the rest are parasitic. At each resonance, the driving-point conductance is large, and the driving-point susceptance is zero. An associated experimental study is described in the paper. The experimental circular array consists of 90 vertical, thin-walled brass monopoles over an aluminium ground plane. The monopoles are electrically short and thick. The single driven element is the extension of the inner conductor of a rigid coaxial transmission line. Narrow resonances are found when the frequency is close to 2.5 GHz. The measured values of driving-point admittance are compared to corresponding theoretical values. Differences between measurements and theory are discussed; the overall agreement is very good. The measured results thus demonstrate the existence of narrow resonances in a physically real array and provide a strong indication for the validity of the underlying theory. The theoretical radiation patterns of the resonant array are discussed, and a potential application as a microwave beacon is described.