A Compact 38 GHz Multibeam Antenna Array With Multifolded Butler Matrix for 5G Applications

A Miniaturized Butler Matrix Based Switched Beamforming Antenna System in a Two-Layer Hybrid Stackup Substrate for 5G Applications

“…Thus, the switched beamforming antenna system is more preferred when precise and continuous beam steering function is not necessarily required, whereas implementation cost and producibility are of 2 of 11 more importance. Passive beamforming matrices such as Blass matrix [3], Nolen matrix [4], and Butler matrix [5][6][7][8][9][10][11][12][13][14] are generally adopted for the switched beamforming antenna system. Among them, the Butler matrix is more widely used due to its wideband characteristic and simple structure.…”

“…Many previous works have been reported focusing on the miniaturization of the Butler matrix. The previous techniques can be categorized into a single-layer substrate based design [5][6][7] and a multi-layer substrate based design [8][9][10][11][12][13][14]. For the single-layer substrate designs, several techniques, such as a higher characteristic impedance transmission line based design [5], a directional coupler employing lumped components [6], and an artificial transmission line employing quasi-lumped elements and discontinuities structure [7], were effective for the miniaturization.…”

“…The multi-layer substrate design approach can alleviate the spurious radiation issue more effectively because the Butler matrix and the antenna elements are placed in different layers. In addition, such previous multi-layer designs have employed further miniaturization techniques, such as the suspended stripline [8], dual transmission line structure in a multi-layer structure [9], forward-wave directional coupler [10], modularized multi-folded structure [11], slot-directional hybrid coupler [12], and dual-layer substrate integrated waveguide (SIW) based crossover elimination structure [13,14]. Yet, it should be noted that those miniaturization techniques inevitably lead to higher implementation cost and less producibility.…”

“…Yet, it should be noted that those miniaturization techniques inevitably lead to higher implementation cost and less producibility. It is also interesting to note, that those previous works [8][9][10][11][12][13][14] have utilized only the same-property homogenous substrates for the multiple layers.…”

A Novel Tri-Beam Antenna System Based on U-Shaped Dipole

“…However, dual microstrip layer are needed for the cross connect, which increase the cost and reduce design flexibility. Based on the SIW and multifolded structure, a 4 × 8 Butler matrix with working frequency of 38 GHz is designed for 5G applications [19]. A low-complexity beam-switching array using a standard 4 × 4 Butler matrix and the phase reconfigurable synthesized transmission line (PRSTL) is demonstrated in [20].…”