Beam-steerable planar array antennas using varactor diodes for 60-GHz-band applications

In this paper we present low-cost and compact beam-steerable planar microstrip antennas for 60-GHz applications. The substrates have three dielectric layers, a ground plane between the bottom and middle dielectric layers, and radiation elements of microstrip antennas on the top dielectric layer. The radiation elements are fed in series by a circuit based on the microstrip-to-slotline transition and the slotline-to-microstrip transition. A feed network of the symmetric structure is developed by fully using the in-phase and anti-phase power dividing techniques. In the feed network, phase shifters using varactor diodes are inserted to steer the beam direction. We fabricated the antennas, measured the antenna characteristics, and evaluated the performance in beam steering. The antenna gain is about 16 dBi, and the bandwidth is more than 4 GHz for a 24-element antenna. Experimental results show that the proposed beam-steerable antenna has the ability of about 7-degree beam steering at the frequency of 60 GHz. Since the phase shifters of this antenna consist of varactor diodes, unlike active phased arrays, the beam-steerable antenna can be fabricated at low cost.