Comparative Performance Characteristics of Yagi-Uda Arrays of Uniform and Varying Lengths of Directors with Uniform and Parabolic Spacings

This paper investigates the comparative performance characteristics between two versions of Yagi-Uda arrays. One version is a twelve-element Yagi-Uda array of varying lengths of directors while the other is a twelve-element Yagi-Uda array of uniform lengths of directors. When use is made of the method of moments technique (MoM), the current distributions on those antennas are determined. The electric field radiated due to corresponding currents as well as the front-to-back ratio, and the relative side lobe level through which the comparative behaviors of the two antennas can be drawn, are evaluated. It is shown that the Yagi-Uda array of varying lengths of directors has greater benefits over Yagi-Uda array of uniform lengths of directors. Those advantages include better front-to-back-ratio (7.1152dB for the former: 26% better, and 5.2331dB for the latter), superior relative side lobe level (-6.998dB for the former: 25% better, -5.222dB for the latter), and greater coverage area of electromagnetic signal transmission and reception. Furthermore, it is found that the two configurations have performance parameters which do not vary to large extents with frequency variation from 400MHz to 410MHz. In addition, it is shown that whena novel procedure of parabolic spacings between directors is adopted in the design, the strengths of the back lobes of the former and the latterunder the same frequencies of 400MHz and 410MHz, are considerably reduced by 44% and 38% while there is corresponding increase in the front-to-back ratios by 42% and 38%, for the two arrays, respectively. Highlighted in the paper are certain practical applications of those antennas.