Design and Fabrication of a High-gain Microstrip-fed Yagi-Uda Antenna

In this report, Yagi-Uda antenna is analyzed and simulated by developing a Matlab program. The analysis of Yagi antenna has been based on considering a single mode cosine current distribution on all elements. The antenna is viewed as a special kind of center-driven dipole array in which all but the actual exciter element are short-circuited at the terminals. Currents are induced in the parasitic elements via the mutual impedances with the exciter, and radiation occurs as from a set of discrete sources. The mutual impedance matrix of the array is calculated using EMF method and integral equations for electric field. This analysis has led to a fast and efficient code to calculate Yagi parameters. The validity of the results is checked with a MoM solution from NEC2, where good agreement has been observed in terms of radiation pattern. Then the code has been used together with genetic algorithm in order to optimize Yagi-Uda antenna for gain maximization. A 31-element high gain Yagi with 19.2dB gain and the gain bandwidth of 8 percent is derived in one optimization. Also the Pareto fronts are plotted for Yagi antennas with different number of elements which shows the trade off between directivity and front to back lobe(F/B) ratio. The effect of genetic algorithm parameters are also studied on the convergence of the optimization. Finally, a high-gain Yagi with 8 elements is fabricated on a dielectric substrate. The measured gain for this antenna at 2.4GHz is 11.4dB and the measured radiation pattern and input impedance shows a good agreement with HFSS simulation.