V-band Bull's eye antenna for multiple discretely steerable beams

The authors present a new approach to designing V-band Bull's eye antennas so as to produce multiple beams, which are either fixed or discretely steerable. Bull's eye antennas comprise concentric rings around a subwavelength aperture. Beam deflection is accomplished by adjusting the effective spacing of the rings, which they explain in terms of the coupling angle to free space and surface waves. They show that multiple beams can be obtained from a single antenna, with the deflection of each beam being controlled independently by the relevant portion of the ring pattern. They demonstrate the principle through rigorous full-wave simulations of two-beam antennas with symmetrical and asymmetrical shifts, and give experimental results for a prototype milled in aluminium, with two separate fixed beams each deflected 16 degrees to either side of the broadside. They also propose means to obtain up to six different beam arrangements during operation by mechanically rotating a plate containing a special six-sector ring pattern. Their simulated example gives three patterns, a single broadside beam or two beams each deflected by 8 degrees or 15 degrees. The radiation efficiency of the antenna is 97% and the gain of a single undeflected beam is 18.1 dBi.