Design and Evaluation of a Closely Spaced Yagi Antenna Over Ground

In this paper, we present the design of a compact Yagi antenna with very close spacing between the elements. The major problem with a Yagi with closely spaced elements is that the radiation resistance is very small, leading to poor efficiency and poor matching. We apply the folding concept to step up the radiation resistance of the antenna to 50 Omega at resonance for element spacing as close as 0.02lambda. A genetic algorithm (GA) in conjunction with the Numerical Electromagnetics Code (NEC) is used to optimize the antenna structure. The optimized antenna design is then evaluated over a lossy ground. The antenna is also compared with other conventional antennas in the same environment