3-D Beam-Steering 2 × 2 Array Antenna With Tunable Frequency Based on the Phase Difference Between Patches

In this letter, we propose a 2 × 2 array antenna capable of 3-D beam-steering and operating frequency adjustment. Each element consists of a patch antenna and a narrow-width I-shaped stub, with two varactor diodes placed between them. By varying the equivalent capacitance values of the varactors applied to each patch, a phase difference between the patches is achieved. As a result, the proposed antenna has continuous beam-steering within the range of −15° to +15° in elevation plane and full 360° in azimuth plane. Additionally, the resonant frequencies of the antenna could be adjusted depending on the equivalent capacitance values between the patch antenna and stub. From the measurement results, the proposed antenna shows continuous 3-D beam-steering of 30° in the 6.87% (2.95 GHz to 3.16 GHz) usable bandwidth.