The effects of reflectors on log-periodic antenna used for High Frequency Surface Wave Radar

High Frequency Surface Wave Radar (HFSWR) is used in ocean surveillance, and single or array of log-periodic-like antenna are often used as the transmitter antenna in flood illumination or beam forming mode. In this work we investigate the effect of reflector rods positioned at λ/4 on log-periodic antenna. Compared with antenna without the reflector, we find the radiation pattern to be more or less similar, but less sensitive to the resonant frequency. Both antenna has large E_θ/E_φ ratio, and the main lobe is pointing at θ=60° elevation and φ=210° and 330°. However, adding the reflector units changes the excitation impedance dramatically such that the return loss is very small, and this renders this arrangement not favorable.