Improvement of scanning beams of a lens antenna by Cluster feeds

In ITS (intelligent transport system) services, antennas are required beam scanning ability. Wide angle scanning can be achieved by introducing Abbe sine condition to dielectric lens surface shaping. Authors designed a dielectric lens antenna that could achieve beam scanning over plusmn30deg. Narrow beam widths were maintained on a scanning plane. However, beam widths on a transverse plane were broadened when beams were scanned over plusmn20deg. And the broaden beam caused a decrease of scanned beam´s directive gain. In this paper, cluster feeds are proposed in order to correct beam broadening on a transverse plane. First of all, the reason of the beam broadening is shown to be phase delays appeared in the antenna aperture plane. In order to compensate the phase delay, the phase advance characteristic is determined in the radiation pattern of the feed. Then the achievement of the phase advance by a radiation pattern synthesis of cluster feeds is introduced. Here, designing radiation phase characteristics is very special trial and effectiveness is not clear. As the first step of designing, the excitation coefficients of the cluster feeds are obtained through LMS (Least Mean Square) method. Next, radiation amplitude and phase patterns of the cluster feed are obtained. By comparing the objective and designed phase patterns, effectiveness of applying radiation pattern synthesis is anticipated. Finally, improvements of beam shapes on a transverse plane and directive gains of scanning beams are shown.