Compact Planar Beamforming Array With Endfire Radiating Elements for 5G Applications

In this paper, a compact 4 × 6 Butler matrix (BM) based on microstrip lines is designed and applied to a linear antenna array. The proposed design creates four beams in four different directions within the 27.5 and 28.5 GHz band. One of the advantages of this BM is a reduction in the size of the beamforming network (BFN). In order to attain this objective, the basic microstrip-based 4 × 4 BM is designed, and then modified to a 4 × 6 BM through a dual-substrate structure to avoid crossing lines using microstrip-to-slotline transitions. The BFN is cascaded with a six-element linear antenna array with endfire radiating elements. The array can be conveniently integrated into the BFN. The resulting design benefits from low-loss characteristics, ease of realization, and low fabrication cost. The array is fabricated and tested, and the experimental results are in good agreement with the simulated ones. The multibeam antenna size is 5.6λ × 4.6λ including feed lines and feed network, while the new BM design is only 3.5λ0× 1.4λ0, which is almost half as large as the traditional one. The measured radiation patterns show that the beams cover roughly a spatial range of 900 with a peak active gain of 11 dBi.