A review of hybrid couplers: State‐of‐the‐art, applications, design issues and challenges

Abstract

In recent years, the hybrid branch‐line coupler has attracted much attention due to its appealing features such as of low cost and ease in fabrication for wireless communications. The fifth‐generation cellular networks promise to support several wireless technologies by capitalizing a multitude of frequencies and increase data rates. To achieve that, the butler matrix technique can be used to enhance both bandwidth and data rate with the implementation of beamforming. Conventional hybrid couplers are the main component to build a butler matrix, but they are generally bulky in size and narrow in bandwidth. Moreover, requirements imposed by newer wireless technologies makes the efforts in improving size compactness and bandwidth even more challenging. On the other hand, several techniques have been proposed in literature to solve both issues. This study focuses on the design challenges and issues of hybrid coupler designs and technologies, besides underlining their promising potential. In this context, several techniques for hybrid coupler to achieve the required bandwidth and size reduction are highlighted, such as the T‐shape, meander line, two sections, three‐section, and parallel couple lines.

A 4 × 4 Millimeterwave-Frequency Butler Matrix in Grounded Co-Planar Waveguide Technology for Compact Integration With 5G Antenna Arrays

“…3(c). By bending the classic square topology [34], fabrication difficulties concerning the required copper pad around each via for full GCPW realization are mitigated, thereby enabling scaling to even higher frequencies. The employed PCB manufacturer's guidelines dictate a copper clearance of at least 0.1 mm.…”

Substrate Integrated Components for Passive Millimeterwave-Frequency Beamforming Networks

“…The components are implemented in GCPW technology, which yields minimal radiation losses and maintains decent power handling capabilities. Additional novelty of the proposed hybrid coupler lies in bending the classic square topology [7], which allows scaling to higher frequencies without introducing fabrication difficulties concerning the required copper pad around each via for full GCPW realization. Additionally, signals can easily be routed to the hybrid coupler under any incoming angle, since the feed lines also exhibit bends.…”

“…Many directional couplers in literature are developed with a designated power ratio [7]. However, for the envisaged Butler matrix beamforming network, an equal power division is necessary.…”

Single-Layer Planar Monopole Antenna-Based Artificial Magnetic Conductor (AMC)

“…Besides that, other techniques such as modification of the ground structure or stacking of multiple substrate layers potentially improve the gain of patch antennas [20]. For the former, several examples include the use of a U-shaped slot, L-shaped arm, or interlocking semielliptical holes in the ground plane, or feeding a rectangular and hexagonal patch using the coplanar waveguide (CPW) technique [21,22].…”