Directivity enhancement of V-band “Bull's eye” antenna with dielectric superstrate

We study the performance of a V-band “Bull's eye” antenna with addition of a dielectric superstrate. We find that a single 0.25mm RF-35 Taconic substrate, at a distance of 6.5mm from the “Bull's eye” antenna structure, allows a directivity enhancement of 2.6dB, to reach 21.6dBi at 60GHz. Efficiency remains almost the same as without and bandwidth is slightly increased. Comparison of the E- and H-plane radiation patterns shows an improvement of the directivity with reduction of the secondary lobes. We discuss the directivity improvement over the frequency band of interest (55-65GHz) and investigate the cause of the enhancement by considering field plots and angle dependant Fresnel reflection from the superstrate.